Armor

Amorphous metals and bulk metallic glasses for armor applications

Steel has many merits as a body armor material, foremost of which are its durability and its ability to be used in very thin sections. Sadly, we’re all familiar with its drawbacks, too — its high density and its near-total uselessness against armor piercing rounds — and not just those made with tungsten carbide cores, but also those rounds with cores of hardened tool steel. But what if steel’s merits could be enhanced, and its drawbacks reduced or eliminated? Recent advances in amorphous metal alloys, also known as bulk metallic glasses, might be just the thing.

Metals and alloys are generally considered crystalline, which means that their constituent atoms are arranged in a regular, periodic, granular manner. Granted, some have extremely complex crystal structures, but they are nevertheless regular and structured. Solids which do not exhibit periodicity — that is, which do not exhibit any regular arrangement of their constituent atoms, and which are fundamentally unstructured — are considered “noncrystalline,” “amorphous,” or “glassy.” Broadly speaking, the arrangement of atoms in an amorphous metal is no different from that disordered or chaotic arrangement of atoms observed in an oxide or silicate glass. And, like these ubiquitous glasses, amorphous metals can generally only be prepared via rapid solidification from a melt — which, particularly for metals as opposed to oxide glasses, involves extremely high cooling rates.

The non-crystalline atomic structure of amorphous alloys lends them unique properties; they are a novel class of material, not quite an “alloy,” not quite a glass, and certainly not a ceramic — but with traits that borrow from all of the above. Broadly speaking, their strength and hardness are greatly superior to crystalline metal alloys, their ductility is reduced, their resistance to abrasion and wear is far higher, their resistance to corrosion is higher. Their impact resistance and toughness vary, with some compositions behaving much like ceramics and glasses, whereas others are as tough as maraging steel. Generally speaking, they tend towards brittleness, as their atomic structure prevents them from arresting growing cracks. Work-hardening is impossible in amorphous alloys, and heat-treatment can turn an amorphous alloy into an inferior crystalline one — so, once made, amorphous alloys are not thermally or mechanically treated.

Amorphous alloys are generally complex from a chemical and metallurgical standpoint. One of the most popular commercially-available amorphous alloys, known as Vitreloy 105, has the following composition: Zr52.5Ti5Cu17.9Ni14.6Al10 (In other words: Zr: 52.5% Ti: 5% Cu: 17.9% Ni: 14.6% Al:10%.) It is therefore characterized as a zirconium-based amorphous alloy, as zirconium is the primary element of its composition. Vitreloy’s complexity is typical of commercial bulk amorphous alloys. But they’re not all complex; the simple ferroboron alloy Fe80B20 can be amorphous, and the first discovered amorphous alloy was a similarly simple Au-Si alloy. As these examples demonstrate, the least complex amorphous alloys are generally comprised of a transition metal alloyed with a metalloid.

Although many amorphous alloys are softer and more brittle than tool steel, certain bulk amorphous alloys — particularly those based upon a foundation of nickel, tantalum, or iridium — have displayed incredible hardness values of 1200 to 2000 HV, which means that the very softest of these amorphous alloys is nearly twice as hard as the best ultra-high-hardness armor steel, and the hardest is significantly harder than armor ceramics such as alumina and reaction bonded boron carbide! What’s more, these amorphous alloys display reasonably good elasticity, stiffness, damage tolerance, and compressive strength. Alloys based upon lightweight scandium, in particular, display outstanding elastic properties combined with good hardness and low density.

The mechanical properties of these aforementioned amorphous alloys, taken together, strongly indicate that they should be capable of defeating armor piercing rounds in thin sections, and may be even more durable and damage-resistant than armor steel.

It is worth noting here that the high-performance glassy alloys mentioned above were not optimized for use as light armor materials. Thus it should almost go without saying that a modern research program could identify and develop better materials; the best light amorphous alloys for armor use; characterized by low density and reasonable materials costs in addition to extremely high hardness, good elasticity, and so forth.

It is highly plausible that thin sections of these hard amorphous alloys would out-perform both steel and ceramics as an armor material. Preliminary work has already done much to confirm this assumption.

If there are hurdles, they’re in the development and bulk production of these unusual metallic glasses. The production methods used for steel and other metals are, in general, wholly inappropriate for amorphous alloy production. Presently-available commercial amorphous alloys like Vitreloy are completely inappropriate for use in armor systems, for reasons which go beyond the fact that they were never optimized for use in armor.

Diamond Age is actively researching bulk metallic glasses and amorphous alloys for armor applications, and is working to overcome the issues associated with their production on commercial scales. We anticipate that our light armor amorphous alloy shall find its way into commercial armor products within the next few years. What’s more, we believe that there’s a sizable market for ultra-high-performance bulk metallic glasses in aerospace, optical devices, and jewelry.

Please contact us for more details.

Armor: Future

Boron Nitride Nanotubes for Armor Composites

Carbon nanotubes have been of broad engineering interest for 25 years. Practical applications, however, are still very few and far between — due primarily to the fact that CNTs like to form aggregates and clumps, which can dramatically impair the mechanical properties of composite materials. It can be extremely difficult to disentangle the nanotubes, and homogenize them within a matrix or spin them into a yarn, without damaging them. Where their incorporation into armor materials is concerned, there’s another problem: Carbon nanotubes are not oxidatively stable, they’re not chemically stable when used alongside certain elements such as iron, and they’re not thermally stable — in fact, they begin to degrade at just 400°C. For these reasons, it is very difficult, if not impossible, to meaningfully incorporate carbon nanotubes into ceramic and metal matrices. Even if chemical compatibility is assured, processing temperatures are always just too high.

Here’s an SEM image we’ve taken of carbon nanotubes at 99% purity:

…As you can see, particularly in the top left, they form particles that look like balls of yarn. These yarnlike particles can be very difficult to disentangle completely.

Boron nitride nanotubes are structurally identical to carbon nanotubes, but are made up of boron and nitrogen at a 1:1 ratio. The mechanical properties of BNNTs are essentially identical to those of CNTs, in that they have an elastic modulus of up to 1.3TPa and a tensile strength of up to 33GPa for individual nanotubes. The thermal properties of BNNTs are also similar to those of CNTs, with, for instance, thermal conductivities measured at 350W/m K and 300W/m K, respectively.

BNNTs differ from CNTs in two key respects:

1. Stability.   High-quality BNNTs are stable to temperatures in excess of 1000°C — in fact, it’s not entirely clear at which temperatures they begin to degrade — so they are highly thermally stable. They are also almost completely inert from a chemical perspective, so are suitable for use in the presence of reactive elements such as oxygen and iron. Their great stability enables and recommends their use in ceramic and metal composite materials.

2.  Ease of use. BNNTs are significantly easier to process than carbon nanotubes. They don’t form aggregates or clumps as readily; they’re not as susceptible to the Van der Waals forces which induce carbon nanotubes to stick together, so are therefore easier to disperse in composite material powders and melts. It is extremely easy to disperse them in ceramic powder slurries with the utilization of common techniques such as ultrasonication or high-shear homogenization.

For example, here are some of our boron nitride nanotubes at 5% loading in a boron carbide powder matrix, where the average particle size (D50) of the boron carbide is in the low nanometers:

At loading volumes generally around 1-5%, BNNTs have already been utilized, experimentally, in ceramic and glass composites — such as in silicon nitride, alumina, and barium calcium aluminosilicate glass. These BNNT composites generally exhibit increased strength and hardness, alongside reduced density, for extraordinary improvements in specific strength. Yet it’s difficult to draw any firm conclusions, as few ceramic-BNNT composites have been reported, and very few metal-BNNT composites have heretofore been reported. This is an area on the frontiers of materials science — and, therefore, of armor science — where much work remains to be done.

Diamond Age is the leading producer of high-density BNNTs suitable for ceramic and metal reinforcement, and is actively researching their use and utilization in the armor systems of the very near future. We have supplied BNNTs to some of the world’s largest electronics and consumer goods companies, and have several patents pending. Please contact us to learn more.

Ceramic Armor It’s said that the development of ceramic armor can be traced back to 1918, to the final days of WWI, when British Army Major Neville Monroe Hopkins discovered that a plate of rolled homogeneous armor steel was much more resistant to penetration if covered with a thin layer of hard enamel. Over twenty-five years later, as Doron was being studied by the Monsanto Chemical Company in the final days of World War II, it was discovered that a solid plate of glass in front of a hard Doron plate was more effective than an equal weight of Doron plate alone. But the first truly modern ceramic armor system dates back to early 1963, and a patent filed by Richard Cook on behalf of the Goodyear Aerospace Corporation. This patent, entitled “Hard faced ceramic and plastic armor,” describes a piece of armor of essentially modern construction: A plate of alumina, or a mosaic of alumina tiles, over a backing of Doron fiberglass

It is unknown to what extent the Cook patent was commercialized or licensed, but it is known that the Army Materials and Mechanics Research Center (AMMRC) started experimenting with ceramic armors almost immediately after that patent was filed. And indeed the Army’s first experimental systems perfectly mirrored the one mentioned in the Cook patent: They were made of alumina ceramic, with a backing material of Doron or aluminum alloy. Coors Ceramics manufactured a small number of these alumina-Doron breastplates for use in the early days of Vietnam, which likely represents the first use of ceramic body armor in combat. The armor was effective — but, as the front and back plates weighed 28 pounds (12.7 kilograms) in total and didn’t dissipate body heat, they were very uncomfortable to wear in the sweltering jungles of Vietnam; thus, like the gleaming steel breastplates of WWI, they were utilized only by aircrews, sentries, and stationary troops. The vast majority of the ceramic armor plates produced over the course of the Vietnam war were issued solely to aircrews; even so, and in spite of the fact that long-range physical mobility is not something frequently demanded of aircrewmen, they found the early alumina plates — colloquially referred to as “chickenplates” — excessively burdensome. Needless to say, infantrymen would have thrown such breastplates away at the first possible opportunity!

The DoD sought out lighter and more comfortable solutions. Small quantities of silicon carbide (“Class II”) and boron carbide (“Class III”) ceramic vests were subsequently produced and issued to aircrews. The class-threes were originally made of hot-pressed boron carbide tiles, arranged in a mosaic-type array of small plates, and were extremely expensive to produce. In 1965, monolithic, multi-curved boron carbide armor plates were developed by scientists at The US Army Natick Research and Development Laboratories and Picatinny Arsenal — an extraordinary engineering achievement at the time. These highly advanced, essentially modern plates were issued to aircrews in very small quantities.

Dr. John Foster, Deputy Director of Defense Research and Engineering in the DoD in the mid-1960s, realized the potential of ceramic armor, and wanted to see how far his department could advance the military applications of ceramic armor. He asked his friend, Dr. Mark Wilkins at the Lawrence Livermore National Laboratories, to spearhead a project which became known as the “Light Armor Materials Program.” The primary goal of this project was to determine the optimal materials and configurations for military light armor — that is, for aircraft, light vehicles, and body armor purposes — and it’s quite impossible to see how the LLNL-based team could have done a better job; the exactingly rigorous and pioneering work of Dr. Wilkins and his colleagues stands out as the most impressive body of work in the field of armor science.

The LLNL team started by preparing a database of all known low-density ceramic materials with desirable mechanical properties for armor purposes, such as high hardness and compressive strength. This list included all of the ceramic materials that are in use today: Alumina, silicon carbide, titanium diboride, and boron carbide. It also included a number of materials that have never seen use, such as the beryllium borides Be2B and Be4B, the aluminum boride AlB12, and the intermetallic titanium beryllide TiBe12, among many others. Wilkins and his colleagues then combined real ballistic experiments with numerical simulations. The experiments included flash radiography, microstructural analysis, the measurement of residual velocities, the analysis of failure modes, and the development of a standardized .30-caliber monolithic hardened-steel test bullet. The 2D numerical simulations were the first of their kind, and the “HEMP” model developed by Wilkins himself and used by the LLNL team was the basis for a great deal of subsequent work in the field.

Following dozens of experiments, Wilkins and his team were able to make a number of general observations which later became effectively axiomatic:

1) The armor needs to be as hard as the bullet (or harder) to defeat the bullet; and the converse is true, thus the reason for tungsten carbide core bullets;

2) The armor layer needs to be at least 1/2 the bullet diameter in thickness to successfully defeat the bullet;

3) The front ceramic needs to be about 1/3 of the thickness of the total plate and the backing needs to be about 2/3 of the total;

4) The basic characteristics of the composite plate are that the front armor material needs to break and turn the bullet and the backing material needs to be ductile to catch the penetrating products without failing;

5) Understanding the fracture/cracking/breakup of the ceramics is only important for thick ceramics, less so for thin sections of armor plate. [1]

These axioms guided the next few decades of armor research. They are only just starting to show their age, as will be discussed here in the future.

Wilkins and his colleagues made a few other noteworthy observations. First, they determined that “functionally graded materials” — that is, materials where the transition from hard to ductile proceeds in a gradual, graded manner, are potentially highly effective as armor materials. What’s more, unlike ceramics and ceramic composites, graded materials can be used for structural, load-bearing purposes.

The LLNL team also determined that inherent ductility in ceramic materials improves performance markedly. Unfortunately, only a few low-density ceramics (the beryllium compounds BeO, Be2B, and Be4B, and magnesium oxide, MgO,) exhibit any ductility, and most of them proved completely unsuitable for armor use. Experiments in ceramic-metal hybrids — cermets — which would presumably exhibit the high hardness and low density properties of ceramics, yet retain some of the ductility of metals, were subsequently pursued. These experiments met with limited success. Cermets with desirable mechanical properties were made — particularly in the titanium carbide-nickel system — but these were relatively high-density materials, at over 5g/cm3. Low-density cermets were not successfully fabricated at that time. Experiments in lightweight systems of presumably high potential — such as, for instance, aluminum-boron carbide — were generally unsuccessful.

The best-performing ceramics in the LLNL’s multi-year survey were the beryllium borides Be2B and Be4B. They exhibited astonishingly low density (<2g/cm3), some measure of ductility, and were hard enough to defeat the steel-cored ammunition of the test. (Though, at roughly 1300HB, likely not hard enough to fare so well against tungsten carbide cored ammunition!) What’s more, they were easy to manufacture; for, on account of their unusually low melting points, they could be cast like aluminum or steel! Despite these merits, and despite the exhaustive and costly evaluations they were subject to, beryllium-based armor materials were never given serious consideration by the US Military. For one thing, inhalation of beryllium dust can be fatally toxic, which fact alone was enough to disqualify it from use in service. For another thing, beryllium is a scarce element and extremely expensive — far too expensive for broad adoption as an armor material. [2]

As boron carbide and silicon carbide armors were in use prior to the establishment of the Light Armor Materials Program, and as no useful material was found that surpassed them, the LLNL’s program had little impact on the course of the Vietnam war. But Wilkins and his colleagues shaped the fields of armor engineering, terminal ballistics, and ceramic fracture mechanics, for decades to follow.

Where armor engineering is concerned, this was not wholly positive. Over the 80s and 90s, staggering efforts were invested in producing silicon carbide and boron carbide cermets. Although some early silicon carbide cermets — with over 60% ceramic content — were eventually used in aircraft armor systems, the material was never issued as part of a body armor system, likely on account of antiballistic inferiority to pure boron carbide and silicon carbide. These cermets were produced by Lanxide Armor Products Co., and their fabrication involved the creation of porous ceramic sponges that were infiltrated with molten metal at atmospheric pressure and relatively low temperature. (Around 1500°C.)

A lightweight aluminum-boron carbide cermet was eventually produced by a different US Military contractor, in a follow-up on some LLNL research on the same system. Although it performed well in ballistic experiments, it was difficult to fabricate and proved far too expensive for broad use, so only a handful of experimental plates were made.

Functionally graded materials have never been successfully produced in bulk for armor or aerospace applications. Despite their initial promise, the manufacturing difficulties associated with their fabrication have thus far been impossible to overcome.

At the time of this writing, boron carbide, silicon carbide, and alumina plates over a ductile backing material still represent the “state of the art,” so to speak, in ceramic body armor. Thus, needless to say, there has been limited technical progress in the field since the mid-1960s. Advances in light armor polymers, e.g. aramid and Dyneema, have rendered fiberglass-reinforced thermoplastics like Doron obsolete, and so the backing layers in armor plates have become lighter, thinner, and more effective — but nothing has yet been found which might replace or improve the ceramic materials which have been in use since the mid 60s.

The major development of recent decades has been the development of reaction bonded silicon carbide and reaction bonded boron carbide. (RBSiC and RBB4C, respectively.) In 1998, Lanxide Armor Products closed up shop. A few years later, their intellectual property rights were bought by M-Cubed Technologies. M-Cubed, doubtless drawing upon Lanxide’s research data and production equipment, then developed the reaction bonding process, whereby molten silicon would infiltrate sponges of either porous silicon carbide and carbon, for RBSiC, or boron carbide, for RBB4C. In the former case, the result is a Si-SiC cermet. In the latter, a composite B4C-SiC-Si cermet.

So-called “reaction bonded ceramics” are relatively easy to fabricate — RBB4C, in particular, is much cheaper and easier to manufacture than hot-pressed boron carbide — a fact which has enabled their production in large bulk quantities. Furthermore, much unlike hot-pressed materials, which tend to be flat plates or discs, reaction bonded ceramics are relatively easy to manufacture in various different geometries and curvatures. But these reaction bonded ceramic materials, which are actually silicon cermets, display inferior mechanical and ballistic properties. RBB4C, especially, is very inferior to hot-pressed boron carbide as an armor material: It is half as hard, it is much less effective at stopping tungsten carbide cored rounds, and it is significantly heavier than hot-pressed boron carbide; it often clocks in at 2.65-2.8 grams per cubic centimeter. The progress of recent years, therefore, has not been without its drawbacks; it has resulted in armor materials that are, in many key respects, actually inferior to those used in the Class II and Class III Chickenplates of the Vietnam War! And yet, with that said, reaction bonded cermets are extensively used in the US Military’s latest body armor systems.

In today’s CONUS police and civilian markets, virtually all ceramic armor systems are made of alumina over aramid. Silicon carbide plates are obtainable, but are fairly rare and relatively expensive. Boron carbide plates are very rare and can be exorbitantly expensive — likely on account of the fact that boron carbide, unlike silicon carbide and alumina, is of limited industrial use, is not produced in huge quantities, and the military’s suppliers don’t sell their armor plates to outside markets.

Mechanical properties of selected armor ceramics:

Alumina (Al2O3) is an ivory-colored ceramic of low cost and ready availability. It is the highest volume armor ceramic in the word due to its favorable cost:performance ratio. It is, however, too heavy for use in modern body armor systems. Typical properties are: Alumina purity (typical): 97-99.9% Density: 3.95g/cm3 Hardness (Vickers): 1200-1600 HV1 Fracture toughness: 3-5 MPa*m1/2 Compressive strength: >2000MPa

Silicon Carbide (SiC) is lighter in weight than alumina, and is slightly superior in terms of performance. The cost of silicon carbide armor pieces is, however, more than five times higher than equivalent alumina pieces — this is on account of the fact that silicon carbide is more difficult to work with, as far higher temperatures and tighter processes are required during sintering. It is generally utilized in high-end body armor. Its crystal structure and molecular characteristics are complex, and will be the subject of a future post. Density: 3.21g/cm3 Hardness (Vickers): 2000-2850 HV1 Fracture toughness: 3-5 MPa*m1/2 Compressive strength: >2500MPa

Nominally B4C,”boron carbide” denotes a number of possible compositions, from the carbon-rich extreme of B4.3C, to, on the other end of the spectrum, the boron-rich extreme of B10.4C.  Commercial boron carbide is generally far closer to the carbon-rich extreme, so it’s not inappropriate to simply use the common “B4C” nomenclature.

Boron carbide is a dark gray ceramic which possesses exceptionally good mechanical properties — particularly in its low density and high hardness.  It is, however, difficult to densify from powder, on account of the covalent nature of its bonding, low surface tension, poor plasticity, and high slip resistance on grain boundaries up to temperatures approaching its melting point.

Processing difficulties mean that it’s generally a very expensive material, and pure hot-pressed boron carbide is extremely rare as a body armor material, but is generally considered to be the best material that money can buy. This is true, with one caveat: Boron carbide armor under-performs against tungsten carbide cored bullets, on account of the fact that its crystal structure collapses (undergoes shear amorphization) under the high pressures typical of ballistic impact from WC-based rounds.

Density: 2.51g/cm3 (pure boron carbide), 2.6-2.8g/cm3 (reaction bonded boron carbide)
Hardness: 2900-3200 HV1 (hot-pressed boron carbide), 1500-1700 HV1 (reaction bonded boron carbide) Fracture toughness: 2.5 MPa*m1/2
Compressive strength: >2700MPa

[1] – S.R Scaggs, 27th Annual Cocoa Beach Conference on Advanced Ceramics and Composites: A: Ceramic Engineering and Science Proceedings, Volume 24, Issue3

[2]-Beryllium’s 2018 price is approximately $2000/kg. Assuming each armor plate of Be2B would require approximately 750 grams of beryllium, and assuming each soldier requires at least two plates, the cost to outfit a division of 12,500 men in beryllium armor would come out to nearly $40 million. Those same soldiers could be outfitted in (admittedly sub-par) alumina plates for significantly less than $1 million, and in boron carbide of the absolute finest quality for less than $5 million.

The first titanium alloys — including the famous Ti6Al4V, which now accounts for more than 50% of total titanium production — were developed in the USA in the late 40s. Shortly after their development, an assessment from Pitler and Hurlich noted that these new alloys showed promise at defeating small arms projectiles. Despite numerous subsequent investigations, experiments, and studies over the 1950s and 60s — which included the development of extremely hard (62HRc) alloys — titanium body armor was never issued to US or NATO soldiers. There is just one exception: River boat crews in Vietnam were issued a light titanium-nylon flak jacket, which was not intended to stop high-velocity projectiles; it was merely a lightweight analog of WWII’s steel-nylon aircrew flak jacket.

Over the ten-year period from roughly 1996-2006, titanium enjoyed a small resurgence in the US as an armor material: Several private US companies examined monolithic titanium body armor plates, the Army Research Labs investigated hot pressing titanium metal powders in 2005, and the now-defunct DragonSkin’s namesake armor vest made use of titanium-ceramic composite armor tiles. Ultimately, these efforts did not meet with much success.

The Soviets, in contrast to the Americans, made extensive use of titanium as a body armor material. In 1979, shortly after the initiation of the Soviet-Afghan war, the 6B2 armor vest was issued to troops on the ground in Afghanistan. The 6B2 consisted of an array of titanium alloy plates, each just 1.25mm thick, bonded to 30 layers of twill-weave aramid. The shell was made of nylon, with Velcro fasteners — and it’s worth noting that Velcro was a very new material at the time, so its appearance on Soviet vests led to speculation as to the vest’s origins. Total system weight was 4.8kgs, including front and back portions. Protection from shrapnel and low-velocity rounds was deemed adequate, but the 6B2 was completely incapable of stopping high-velocity aimed projectiles. In fact, it reportedly could not stop 7.62x39mm rounds fired from distances of 300-500 meters. The 6B2 was therefore much like the Vietnam-era flak jacket in many respects, even in appearance, but markedly heavier.

The 6B2 was quickly replaced in service by the 6B3TM, a still heavier version, where the thickness of the titanium plates was increased to 6.5mm. This change increased the weight of the vest to 12kg. It was then changed again, in the 6B3TM01, to a version with front plates which were 6.5mm thick, and rear plates which were 1.25mm thick. [1] This final version was roughly 9kg in total weight. Having said all of that, it is exceedingly unlikely that 6.5mm-thick plates of titanium would stop 7.62x39mm or 5.56x45mm rounds at anywhere near muzzle velocity — but they would have done the job at engagement distances of 200-500+ meters.

In 1985, midway through the war, the 6B4 was introduced. This was an armor vest made of boron carbide and aramid, similar to those issued to certain soldiers in Vietnam, doubtless of much greater protective ability than the titanium armor vests which preceded it. Ceramic strike faces feature heavily in subsequent models of Soviet and Russian armor — though, until quite recently, body armor in Russia often comprised titanium and steel portions. This appears to have been eschewed entirely in recent years; the most advanced Russian model at present, the 6B46 “Granite 5a” armor plate, appears to be made entirely of silicon carbide over aramid.

Mechanical and ballistic properties of selected titanium alloys used in modern armor systems:

Ti6Al4V is an alpha-beta titanium alloy comprised of 90% Ti, 6% Al, and 4% V. It has a density of 4.43g/cm3, a hardness of 334HB, a yield strength of 880MPa, tensile strength of 950MPa, charpy impact at 17 J, and elongation at 14% in 2″. It has a shear strength of just 550MPa.

Russian Armor-Grade Titanium is a titanium alloy also comprised of 3% Al, 5.15% V, 3.65% Cr, with trace amounts of boron, zirconium, and molybdenum. It has a hardness of 387HB, and a density of 4.62 g/cm3. Its other properties are unknown, but it is not unreasonable to assume that it possesses greater yield strength and tensile strength than Ti6Al4V, an inferior charpy impact strength, and inferior elongation.

Adjusted for weight, the US Army Research labs have determined that the ballistic performance of Ti6Al4V is superior by roughly 7% to that of the aforementioned Russian alloy. Adjusted for weight, I repeat. As Ti6Al4V is about 5% lighter, what this means is that the two alloys perform nearly identically at equivalent thicknesses. The differences in mechanical properties are apparently not of great importance; the lighter alloy performs better largely on account of its lightness; if titanium alloys are still of interest to body armor designers, I’d imagine that one priority should be the development of a lightweight titanium armor alloy — perhaps with a higher volume fraction of aluminum.

In any case, as the above paragraphs clearly show, both titanium alloys possess a great strength-to-density ratio, and both are comparable in hardness to rolled homogenous armor (RHA) steel. What is less obvious is titanium’s propensity to fail via plugging, which markedly reduces its utility as a standalone armor material. When a titanium alloy plate is struck by a high velocity projectile, shear strain, strain rate, and temperature can rise to very high values over a very small surface area. Titanium’s relatively poor shear strength, combined with its very poor heat transfer properties, make it inherently susceptible to fail catastrophically in such situations via a phenomenon known as adiabatic shear plugging. This problem becomes almost insurmountable when titanium alloy armors are used at low thicknesses — thicknesses typical of body armor! For this reason, it is our view that the further development of titanium as a body armor material is not warranted.

[1] This is reminiscent of earlier eras. As was noted in a previous post, Alexander the Great and the tacticians of the 16th century both recommended that little-to-no armor be worn on the back, “on the ground that it [is] unnecessary, and that its absence would discourage cavalry from turning its back to the enemy.” This is, to a certain extent, nonsensical in modern warfare: Epidemiological studies indicate that the back sustains just as many injuries as the front, from shrapnel in particular. However, the back doesn’t need as much protection from rifle fire — as it is also quite typical that 70-80% of battlefield casualties who have sustained bullet wounds were shot from the front; bullet entry wounds in the back are markedly less common.

The first truly modern woven armor material — a laminate comprised of layers of woven glass fabric, impregnated with an ethyl cellulose resin, and bonded under high pressure — was invented by the Dow Chemical Company in May 1943. Initial reports were promising, and the Military Planning Division, Office of the Quartermaster General, under the command of Colonel Georges Doriot, launched the “Doron project” to find suitable applications for this new material. (“Dor” from the Colonel’s name, +”on”, from the generic ending for fibers such as rayon, nylon, cotton, etc.)

Doron was first used in battle in August 1944. The T37 flak vest for airmen was a straightforward design where the steel plates of the ubiquitous M1 flak jackets were replaced by flat hot-pressed Doron plates approximately 50mm square and 3.3mm thick. Later modifications utilized thicker, curved Doron plates. The T37 and its derivatives remained experimental, however; they were not adopted by the Air Force, as aluminum and nylon-based solutions were deemed more suitable for use at that time. The Army, following the Air Force’s lead, did not engage in further experiments with Doron over the last days of WWII.

Which is not to say that nobody was interested. The US Navy remained keenly interested in Doron, and pioneered its research and development in armor systems.

Two Naval officers, Lt. Commander Edward Corey and Lt. Commander Andrew Paul Webster, were the first to test the personal protective ability of Doron — and they did this in an unusual and brave, if not foolhardy, way: Lt.Cdr Corey wore Doron panels, with various backing materials, over his arms and held them in his hands, as Lt.Cdr Webster fired at him with a .45 pistol. A short account of their tests follows:

“Dr Corey, with a great deal of physical courage, volunteered to be the subject of this test. The strain of this first test is understood when one considers that we did not know whether his arm would be torn off by the blow from the bullet or whether I would even hit the armor on his hand. The shots proceeded as follows. When Doron was backed with [a 1 inch layer of] sponge rubber or a heavy layer of kapok, the impact of the bullet on the hand resulted in no discomfort, and even with a few thicknesses of duck cloth no injury resulted. The bullets were literally picked out of the air and caught as if catching marbles flipped at the hand. When the backing was reduced to a single thickness of duck cloth, severe bruising resulted, with hematoma, pain and edema, but without fracture. Deep sensation did not return in the hand for a period of about six weeks. It was concluded from these experiments that since our problem of armouring ground troops and shipboard personnel was one involving maximum protection and comfort for minimum weight, no backing should be used.”

The folks who today obsess over BFD and behind-armor trauma should read that last part again.

The Navy subsequently utilized Doron in two forms: By sewing Doron panels into pockets on the outside of the Kapok lifejacket, and by sewing Doron panels into the standard-issue Marine Corps utility jacket. Roughly a thousand such jackets were prepared for use in the Battle of Okinawa, but, unfortunately for the development of body armor if not for the men involved, the Marine division outfitted with the armored jackets was not involved in the fighting.

Doron, ballistic nylon, and doron-nylon vests were again tested during the Korean War. For the first time in modern history, these body armor experiments were judged a complete operational success. The Doron vests were popular with Army troops, commanders, and battlefield physicians alike, to the extent that the body armor evaluation team wrote in its final report:

“The effect of body armor on confidence is probably best expressed in the results of the post-use interviews where over 85 percent of the men stated that they felt safer and more confident when wearing body armor.”

“Interviews with commanders, who have led troops wearing body armor in combat, have repeatedly emphasized that aggressiveness is increased and that there is more of a desire and willingness to engage the enemy at close quarters.”

“A poll of over 100 front line physicians and surgeons has resulted in the almost unanimous expression of opinion that the use of body armor would result in an increase in morale among combat troops.”

“Under certain conditions the effect of body armor on morale may not be good. For example, during the last month of the test period there were several instances where soldiers who had previously used body armor expressed a reluctance to their unit leaders to go out on patrols when body armor was not available.”

More than anything prior, this glowing evaluation of Doron and nylon armor in Korea cemented body armor’s place in the modern soldier’s kit.

Given the Navy’s interest in Doron vests during WWII, it should come as no surprise that the Marine Corps were early adopters of body armor – and, throughout the course of the Korean war, all Marine Corps frontline personnel were armored in Doron-Nylon flak vests. The Army, at the same time, was still evaluating Doron and nylon vests on a very limited trial basis. As positive feedback from these trials started to come in, and as positive reports from the Marines reached Army HQ, the Army decided that they needed to hurry up and issue body armor to all of their frontline personnel as well, so they requested 13,020 Marine vests on August 11, 1952. By the end of the war, the Army had procured well over 25,000 Marine Corps vests. It should go without saying, therefore, that the Marine vest, the M-1951, was the Korean War’s predominant form of body armor. It weighed 7.75 pounds and was a sleeveless vest with a zipper closure in front. It was made of 1050 denier ballistic nylon fabric and hard Doron fiberglass plates. The shoulder girdle area was protected by 12 layers of ballistic nylon, which was flexible and reportedly comfortable to wear; the chest, abdomen, and back were covered in sixteen curved, 3.175mm thick, overlapping Doron plates.

The Army, following further evaluations, ultimately decided to adopt a different design. The Army personnel assigned to the development of armor projects believed that ballistic nylon was just as effective as Doron, but easier to wear on account of its flexibility and ability to drape. Thus the all-nylon M-1952 was issued to troops over the last months of the war, starting in February 1953. Like the M-1951, it was a sleeveless vest with a zipper in front. It had two front and back panels composed of ballistic nylon bonded with laminating resin, but this was still reasonably flexible, and the vest was reportedly comfortable to wear. It weighed 8.25 pounds, so was slightly heavier than the M-1951, but its flexibility made up the difference.

The M-1951 and M-1952 remained essentially unchanged into, and over the entire course of, the Vietnam war. There were minor, mostly cosmetic, upgrades — but the weights and materials did not differ to any meaningful extent. The vest of the Marine Corps in Vietnam was designated the M-1955, which was, like the M-1951 it replaced, made of ballistic nylon with Doron plates. The Army vest, the M-1969, was of all-nylon construction. It was identical to the M-1952, save for the addition of a high collar, which added roughly half a pound to the vest’s weight, and which soldiers generally disliked, as it interfered with the wearing of the M-1 helmet.

Enter Kevlar. Just as the Vietnam War was ramping up, in 1965, DuPont scientist Stephanie Kwolek was working on a research project tasked to find high-tensile-strength fibers for use in reinforcing automobile tires. To this end she was experimenting with the stiff polymer precursors poly-p-phenylene terephthalate and polybenzamide, when she noticed that the reaction product of the two precursors displayed some unusual properties. As she later explained:

“The solution was unusually (low viscosity), turbid, stir-opalescent and buttermilk in appearance. Conventional polymer solutions are usually clear or translucent and have the viscosity of molasses, more or less. The solution that I prepared looked like a dispersion but was totally filterable through a fine pore filter. This was a liquid crystalline solution, but I did not know it at the time.”

Unusual-looking chemical solutions of that sort were not often pursued; they were usually considered failed or abortive experiments. Kwolek went on to mention that “I think someone who wasn’t thinking very much or just wasn’t aware or took less interest in it, would have thrown it out.” But she persisted, so the solution was spun on a spinneret, and the mechanical properties of the resulting fibers were tested. It quickly became apparent that this new “aramid” fiber was three times as strong as nylon and possessed a far higher modulus and heat resistance. And, despite its high modulus, even these first fibers were so fine that woven fabrics derived from them were flexible, and were able to drape like nylon.

The military quickly realized the potential of this new material, though they didn’t rush to implement it in armor systems and issue it to troops in Vietnam. Military-grade aramid fabrics were first designated as PRD-29, and PRD-49 — and later as Kevlar® 29, which was previously PRD 49-IV, and Kevlar® 49, which was PRD 49-III. Kevlar 29 was judged the superior grade for ballistic protection, and prototype flak vests were made which offered significantly greater protective ability than those made of nylon and Doron, at the same weight.

In June 1978, vests comprised of 13 layers of Kevlar 29 ballistic fabric within an envelope of water-resistant ballistic nylon were issued as the “Body Armor Fragmentation Protective Vest, Ground Troops” for United States soldiers. In the early 80s, this type of vest was standardized as part of the PASGT armor system, which also included a helmet made of resin-bonded laminate Kevlar 29. The PASGT system was quite long-lived — it remained in use by the US military until the mid-2000s, and still remains extremely common worldwide, as it was extensively exported. The PASGT’s successor, the Interceptor Body Armor system, was also made of aramid — in this case, the improved KM2 fiber. The most recently fielded body armor system, the Improved Outer Tactical Vests, which are a partial replacement for the Interceptor, still incorporate aramid fibers in their soft armor component.

Yet this is not to say that aramid is the only option, nor should it even imply that aramid is the best option.

Scientists at DSM in the Netherlands discovered ultra-high molecular weight polyethylene (UHMWPE) fibers by accident in 1963, during experiments in fractionating out different polyethylene lengths from a solution. It was immediately noted that these very long-chained polyethylene molecules were incredibly strong, but, initially, only small amounts were produced, and it seemed impossible to produce meaningful quantities. This is on account of the fact that the UHMWPE fibers were nearly impossible to orient in solution, so they’d typically form intractable aggregates and clumps, and only a small fraction of each production batch would result in usable UHMWPE fibers.

(Spaghetti is the usual analogy. On a molecular level, strong UHMWPE fibers resemble bundles of stiff, uncooked spaghetti. UHMWPE in solution resembles tangled clumps of soft, overcooked spaghetti. The art of drawing strong Dyneema fibers — and it is an art — resembles turning cooked and tangled spaghetti into uncooked spaghetti!)

In 1978, 15 years after the original discovery, DSM engineers discovered the ingenious gel-spinning method, which enabled the production of commercial quantities. Dr. Piet Lemstra, who worked on the project, described as follows:

 “It’s actually very simple. The more you dissolve the long chain molecules in a solvent, the more they become separated. Then you cool it down to a gel state and the molecules are more or less disentangled, so it is easy to stretch them. You can then remove the solvent, or later, during the stretching/drawing process – either way you end up with nearly perfectly aligned molecules.”

Although the development of this clever gel-spinning process enabled the industrial production of UHMWPE fibers, DSM was not an industrial fiber company. It was — and to a large extent remains — a food and agricultural supply company that discovered UHMWPE fiber by accident. The UHMWPE team at DSM was essentially a “skunkworks” crew that did their experiments in spare time and on weekends, with little corporate oversight. In the years since its discovery and the development of a commercial production process, the decision-makers at DSM showed no interest in commercializing UHMWPE fiber, and this was not helped by the fact that the consulting companies they asked to evaluate their potential product did not think very highly of it.

“This [consulting] company said the fiber was just candlewax unable to resist high temperatures and it lacked any good properties. They saw no future in it,” says Lemstra. “And the management at DSM believed them.”

Around that time, in the very early 80s, Allied Signal (now Honeywell) obtained a patent on a very similar UHMWPE fiber product, though they claimed that the melting point of their material was 20-30 degrees higher than that of DSM’s fiber. As it turned out, the two UHMWPE fibers were largely identical, the melting point differences were due to an methodological error on Allied Signal’s part, and, as the DSM patent had priority, Allied was compelled to purchase a license for the original DSM patent.

With the license in hand, and no potential intellectual property conflicts on the horizon, Allied started marketing their own fiber, Spectra, as a competitor to Dupont’s Kevlar. Dupont countered with effective marketing campaigns which showed how Spectra would weaken at moderately high temperatures — from 60-80°C. The military, aided by institutional inertia, essentially said “if it ain’t broke, don’t fix it,” and stuck with aramid armors.

It could be argued, in hindsight, that Allied and DSM didn’t do enough to promote their material. Yet, at the same time, the first grades of UHMWPE fiber were quite poor. We have seen continual improvement since those early days, and today’s grades of UHMWPE fiber are more than 44% superior to the best grades of Kevlar on an equal-weight basis.

Dyneema and Spectra are presently used in high-end body armors, the very newest models of military helmet, and lightweight ballistic shields. Unlike aramid, moderately thick panels of UHMWPE (2cm+) are capable of stopping lead-cored rifle rounds at high velocity, but invariably fail against steel-cored rifle rounds. In fact, they can fail against steel-core pistol rounds; that the SS190 AP 5.7x28mm pistol round can punch through a UHMWPE Level III plate has been documented.

In any case, there’s significant room for improvement in UHMWPE fiber materials, and it’s likely that further gains will be made within the next 10-15 years.

Mechanical properties of selected woven and polymer armor materials

Fiberglass

E-glass fibres, manufactured from alumino-borosilicate, are the oldest armor fibers in modern use, as their use dates back to WWII’s Doron. This grade of fiberglass is infrequently used in modern body armor systems, but, on account of its very low cost, is often encountered as a spall mitigation liner in armored vehicles.

S-glass, of magnesium-aluminosilicate, is a superior grade of fiberglass with much-improved mechanical properties: lower density, higher strength, greater stiffness, and a 20% improved strain-to-failure. However, even the best-performing glass fibers perform only roughly half as well as aramid for ballistic applications.

E-glass
Density: 2.6g/cm³
Ultimate Tensile Strength: 3450 MPa
Modulus of elasticity: 72.4GPa
Elongation at break: 4.8%

S-glass
Density: 2.48g/cm³
Ultimate Tensile Strength: 4750 MPa
Modulus of elasticity: 90GPa
Elongation at break: 5.7%

Aramid

Aramid is, without doubt, the most ubiquitous ballistic fiber in the world at the time of this writing. It is extensively used in standalone body armor systems, spall liners and backings, ballistic helmets and shields, and virtually every other conceivable application — including “armoring” fiber optic lines for extended stays in harsh environments, and armoring satellites from micrometeorite impact. It has excellent resistance to fire and heat, but is sensitive to UV light (photooxidative degradation) and humidity (hydrolysis), so it is typically sealed or coated prior to use, and its characteristic bright yellow color is infrequently seen.

Aramid – Kevlar 29
Density: 1.44g/cm³
Ultimate Tensile Strength: 3620 MPa
Modulus of elasticity: 70.3 GPa
Elongation at break: 3.6%

Aramid – Kevlar KM2
Density: 1.44g/cm³
Ultimate Tensile Strength: 3880 MPa
Modulus of elasticity: 84 GPa
Elongation at break: 4.52%

Ultrahigh Molecular Weight Polyethylene

Broadly speaking, this class of polymer composite offers the best performance-to-weight ratio. More specifically, there are a number of grades available, ranging from low-cost grades with a weight efficacy roughly equal to aramid, to very highly-optimized grades, such as Dyneema SB-117 and Spectra Shield 5143, that are much more effective than aramid on a per-weight basis.

UHMWPE is stable in the presence of UV light, but has a low melting-point that leads to performance degradation at high temperatures. This becomes a serious consideration at temperatures over 70°C.

UHMWPE – Spectra 1000
Density: 0.97g/cm³
Ultimate Tensile Strength: 2570 MPa
Modulus of elasticity: 120 GPa
Elongation at break: 3.5%

Note: The antiballistic properties of Dyneema HB212 are significantly better than Spectra 1000, but its mechanical properties have not been made public in a comprehensive way.

Carbon Fiber

Carbon fiber is a structural composite that’s rarely used as a ballistic material on account of its brittleness, relatively high density, and lack of ductility. It boasts an extremely high yield strength and flexural modulus, however, and its strength and stiffness make it attractive for certain niche applications in armor. It is also highly resistant to UV light, chemical exposure, and temperature extremes. The very best grades of carbon fiber — Toray’s T1100G (ultra-high strength) and M60J (ultra-high stiffness) — represent the current state of the art, and are uncommon, whereas the grades T300 and T800 represent the fibers most frequently used in aerospace and automotive applications. T300, in particular, dominates the carbon fiber industry — 95% of sales are of the “standard modulus” T300 grade.

Carbon Fiber – Toray T300 (Standard modulus)
Density: 1.55g/cm³
Ultimate Tensile Strength: 3800 MPa
Modulus of elasticity: 230 GPa
Elongation at break: 1.5 – 1.76%

Carbon Fiber – Toray M60J (Ultra-high modulus)
Density: 1.93g/cm³
Ultimate Tensile Strength: 3950 MPa
Modulus of elasticity: 588 GPa
Elongation at break: 0.7%

As the previous post noted at length, steel has been used in armor from ancient times. It is still the world’s most ubiquitous armor material, on account of its excellent mechanical properties, coupled with the fact that it is an extremely low-cost solution.

Steel body armor, as a means of defeating high velocity aimed projectiles, was extensively used in WWI. Its use was generally experimental, and the experiments generally received poor-to-middling feedback, thus at no point in the war was steel body armor common. Soldiers generally found it burdensome, and not worth the effort of wearing, which is little surprise, as the steel body armor of those days was both thick — regularly weighing in excess of 30lbs — and it offered imperfect protection, being roughly equivalent to the flak jacket of later eras. For these reasons, taken together, the use of steel armor was generally relegated to soldiers in more-or-less stationary positions: Sentries, machine gun crews, and sappers. Even so, the use of steel body armor was judged a failure, and its use all but disappeared in the days following WWI. [1]

The poor feedback had much to do with the fact that 81% of WWI’s combat casualties were due to rifle and machine gun fire, against which steel armor offered no meaningful protection. Yet it must be noted that this is anomalous, for in WWII and subsequent wars, casualty statistics indicate that 70-80% of casualties were due to fragmentation, explosions, and indirect fire, and only 20-30% of casualties were due to direct rifle or machine gun fire. It stands to reason that the widespread use of steel body armor — or any armor — could have saved many lives in WWII. [2]

It is unfortunate, then, that steel armor saw only very limited use in that war. British and American field tests, in 1941, with manganese steel vests were judged unfavorably; all reports indicated that the advantages they might bring their wearers would be negligible compared to the loss of combat efficacy and the increased carrying load — despite the fact that the body armor system in question was around 1.5mm thick, on average, and weighed less than 3 pounds in total.

In 1942, following reports from aircrews of extremely dense flak that would punch through airframes and injure crewmen, the UK Royal Air Force started issuing steel armor to its aircrewmen. The armor they developed was initially comprised of 1mm thick manganese steel plates, 2 inches square, sewn into pockets, over a backing of flax canvas. It was offered in different cuts, from full-cuts which included leg and groin protection, generally intended for gunners who had to operate from a standing position, to vests which covered the front of the torso only, generally for pilots. Depending on the extent of coverage they provided, the weights of these early flak armor suits were from 4.5 to 16 pounds.

The US quickly adopted the design, and issued flak jackets to US Air Corps aircrewmen and US Navy personnel on aircraft carriers. The composition of the steel remained identical from a metallurgical perspective, and the thickness and size of the plates was not changed, but the backing was upgraded from canvas to ballistic nylon, a fact which increased performance considerably. Late in World War II, when flak jackets were ubiquitous among airmen, there was a reduction of 60% in the total number of combat-related wounds.

While these nylon-steel flak jackets were in use, the United States Army and Navy were busy trying to find a more efficient armor. More efficient, in this context, meaning lighter weight and enhanced protection. The development of Doron, a laminate of fiberglass and polyester resin, achieved both of these objectives. At an equivalent weight, the new fiberglass composite was significantly more protective than steel or aluminum; at a meaningfully lighter weight, it still offered slightly more protection. Following the adoption of Doron, which will be further discussed in a future post, steel was supposedly rendered obsolete as a body armor material, and gradually passed out of active military service. [3]

As it turns out, the reports of steel body armor’s death were greatly exaggerated, for it has enjoyed a marked resurgence in recent years. AR500 — an industrial grade of abrasion resistant steel with a Brinell hardness of approximately 500, thus “A R 500” — had initially been marketed as a steel target material, made possible by its ability to resist penetration from rifle fire in thin sections, and popular due to the satisfying sound and sparks it makes upon impact, which are audible and visible from great distances. Around 2011-2012, private US companies began selling AR500 armor plates to the civilian and law-enforcement markets in earnest. These plates were approximately 6.3-6.5mm thick, weighed 7.5lbs (3.4kg) in the popular 10×12 inch “shooter’s cut,” and were generally, but not always, coated with a layer of polyurea to mitigate spalling and help prevent ricochets. Ballistic testing showed that such plates generally had little problem resisting multiple shots from the 7.62×51mm M80 Ball and similar rounds, and could stop M855 at muzzle velocity, but were likely to fail against extreme-high-velocity rounds, such as 5.56mm M193 rounds traveling at 3100+ feet per second — velocities typical of shots fired at close range from a 16″+ barrel. AR500 armor plates are wholly incapable of stopping AP rounds at typical engagement distances, even such lowly AP rounds as the 7.62x39mm API-BZ. Yet on account of their low thickness, durability, wide availability, and extremely low cost at less than $100 per plate at retail, AR500 armor plates very quickly became the most popular form of rifle-rated armor on the civilian market. Indeed, plates seemed to sell faster than the manufacturers could produce them!

As of 2016, major military contractors and armor OEMs, doubtless taking a cue from AR500 Armor, had begun to offer steel armor plates. The most noteworthy of these was Tencate’s 8075SA, which, at a thickness of just 5.08mm and a weight of 6.2lbs (2.83 kg), was claimed to stop the M193, M855, M80 Ball, and 7.62×39 PS Ball rounds — all at muzzle velocities from full-length barrels. 2.83 kilograms is still, however, markedly heavier than the ceramic composite plates currently available, and all steel plates are, again, incapable of stopping steel-cored AP rounds. The 8075SA was also noteworthy for its unusually high price — it retailed for several hundred dollars per plate, and as of January 2018 seems to have been discontinued, presumably due to low demand.

The militaries of the world have, as yet, shown little-to-no interest in steel armor, though the civilian market for such plates continues to thrive. I believe that this is unlikely to change in the near future.

I’ll mention in passing that steel, and often very good grades of steel, remains the premier material for use in vehicular armor. In light of this, it’s also worth mentioning that the vehicular armor market is roughly ten times larger than the body armor market. Steel remains, therefore, the world’s premier armor material.

As for the mechanical properties of selected steel alloys used in modern armor systems:

AR500 is a low alloy steel, of medium carbon content (0.31%), quenched and tempered to a hardness of approximately 500HB. It is weldable. Yield strength is typically 1515MPa, tensile strength 1620MPa, charpy impact at 24 J, elongation at 14% in 2″. It costs roughly $2/kg in bulk, and is among the cheapest armor-grade steels available, likely due to its lean metallurgical profile, along with the fact that it’s produced in bulk for industrial use. (Nickel-rich and cobalt-rich alloys are much more expensive, as are high-strength specialty steels that are only produced in small batches.) The US military specification MIL-DTL-46100E “High Hardness Armor,” is closely analogous to AR500, but is intended for vehicular use.

ARMOX Advance is a ultra-high hardness steel used primarily for vehicular armor, but also of interest for body armor. It is a low alloy steel, with nickel as the primary alloying element. It is quenched and tempered to a hardness of approximately 670HB. Yield strength is 1600MPa, tensile strength 2250MPa, charpy impact at 14 J, elongation at 9%. Armox claims that just 4.5mm of Armox Advance can defeat the 5.56x45mm M193 at 937m/s or 3075fps — just a couple hundred feet per second below muzzle velocity.

Deutsche Edelstahlwerke Megafort-Z (previously Thyrodur Z) is a Ni-Cr-Mo-alloyed steel marketed as a premium vehicular armor material. It can be quenched and tempered to a hardness of approximately 575HB. At this hardness, tensile strength is 2000MPa, and elongation is over 14%. A 3.8mm thick panel of Megafort-Z can defeat the 7.62×39 PS Ball round at 700 m/s, which is muzzle velocity. This is a very impressive feat.

Armox advance and Megafort-Z represent, each in their own way, the high-end of the steel armor market, whereas AR500 is without question the most common alloy used for body armor today.

For comparison’s sake, the armor steel used in the flak jackets of WWII, Hadfield steel, was an austenitic manganese steel with a carbon content of 1.2% and a manganese content of 12%. Its tensile strength was approximately 500MPa and its yield strength was 860MPa. Hadfield steel is not a very hard steel, at generally just 240HB — however it shows extensive strain-hardening effects, and can reach hardnesses of over 400HB (along with correspondingly higher strength) upon impact or if pre-treated via compression or shot peening.

It may be interesting to note that there are maraging steel grades which exhibit tensile strengths higher than 3100MPa, combined with great elongation and fracture toughness, and hardness values which exceed 700 HB. (!!) These maraging steels are, however, chemically complex, and orders of magnitude more expensive and difficult to produce than low alloy steels. (I’ve seen maraging steels cost as much as $345/kg, and there are surely even more expensive grades.) Their production and export are also tightly controlled, as steels of this extremely high grade are often used to manufacture centrifuges for the separation of nuclear materials. For these reasons, maraging steels with tensile strengths over 2300MPa have never been utilized in military armor. Their military uses are presently restricted to missile skins and other applications where strength is prioritized at any and all costs.

It is frequently said that steel metallurgy has been exhausted — that it’s unlikely that future steel armor systems will be able to improve significantly upon the current state of the art. This is an erroneous belief, but that’s a matter for a future post.

[1] An interesting aside is that the design of the modern military helmet dates back to WWI. Dr. Bashford Dean, the author of the previous post, contributed a number of helmet designs to the US Army, one of which rated very highly, but was judged to be too similar in appearance to the standard-issue German helmet of the time, so it wasn’t approved for use! The German helmet was itself based on a medieval design, and was judged to be the most effective helmet of its time.

[2] There are numerous personal accounts of this, but the very best is the famous “Company Commander: The Classic Infantry Memoir of World War II” by Captain Charles B. MacDonald. The use of artillery in Captain MacDonald’s account was seemingly ubiquitous — it featured in every action and every operation — and the vast majority of the casualties mentioned in the book were hit by shrapnel from shells or mortars.

[3] Although steel body armor passed out of military use a very long time ago, the steel M1 helmet remained in use until the early 80s, at which time it was replaced by the Kevlar PASGT helmet. Interestingly, the M1 and the PASGT are very similar in weight, are quite similar in ballistic protective ability, the M1 is significantly cheaper to produce, the M1’s liner made for a one-size-fits-all solution, and soldiers in the field have always found the M1 useful for cooking and shaving, whereas the PASGT was useless for those purposes… so one could certainly call into question the wisdom and necessity of the M1’s replacement! The Kevlar PASGT, although of similar performance vs. bullets, does, however, exhibit a much higher V50 versus fragments and fragment-simulating projectiles.

To launch a blog about armor, I believe that it may be best to start with a review of its historical uses, from antiquity to World War I. The author of the following historical account, the very eminent armor expert and historian Bashford Dean, has already written such a review. It can hardly be improved upon, so I shall incorporate it in its entirety.

The author, in his own words, has sought to answer the following questions:

(A) What kinds of armor were early used?

(B) Was armor actually an important means of saving life and limb?

(C) How was it made?

(D) How was it tested?

(E) How heavy, irksome and even dangerous was it to wear?

(F) What in summary was its use in later times but prior to the Great War?

It should go without saying that the answers to these questions set the stage for the discussion of modern armor — and, what’s more, that the reasons for the disappearance of armor from the battlefield has much to teach the modern armorer. So although it might seem unusual to launch a technology blog with a thorough review of the now-distant past, Mr. Dean’s fine work should make it clear that our forefathers still have much to teach us, and their techniques and lessons are worth careful study.

I have taken the liberty of italicizing passages which I deem to be especially relevant.

If there’s one significant take-away message, if there’s a “bottom line,” it is that armor wasn’t simply abandoned because it was ineffective against the musket and arquebus. To the contrary, it was strikingly effective; yet the development of firearms forced armor to become increasingly heavy and increasingly plain. Subsequently, strenuous infantry tactics reminiscent of modern maneuver warfare, which had begun to be implemented around the time of the Thirty Years’ War of the mid 17th century, encouraged soldiers to do away with as much of their armor as possible. Thus armor became, in the words of Mr. Dean, “unfashionable, then unpopular and in the end discredited” among fighting men.

It therefore follows that the aim of the modern armorer — to strike the best balance of performance and weight — is a well-founded one, but that there’s more to it than just that: Tactics and the realities of war must also be taken into account.

Adapted from Helmets and Body Armor in Modern Warfare, published 1914.

By Bashford Dean.

HELMETS and body armor are usually considered as objects beautiful, rather than useful. They are exhibited in museums, in halls hung with tapestries, beside faience, ivories and enamels of olden times. Some of them were designed by artists whose names are highest of all in the history of art, Raphael, Leonardo, Donatello, Holbein, Michael Angelo and those who actually made and decorated the armor were masters hardly less distinguished. Certainly in their day they were paid the highest honors. Seranno di Brescia, armorer of Francis I, was received at court on the same footing with Titian; the Milanese Missaglia lived in princely splendor, and Seusenhofer, the helm-smith, was one of the intimates of the knightly Maximilian.

It is, then, from the viewpoint of artistic excellence that armor has largely been treated, especially as to its decoration and its various forms. Its technical side is little known, and few there are, even among specialists, who have considered how difficult armor was to make, and how time consuming, for a suit of armor of high quality might cost its maker years of labor. And, particularly, little is known as to its usefulness in combat, which, none the less, was the main if not the only reason for its existence. Armor, in a word, has been studied as a dead language or, better perhaps, as the bones of a fossil animal, which the anatomist examines attentively and from which he is led to explain the habits and capabilities of the animal itself. Nevertheless, there are clearly other paths leading to a knowledge of armor which deserve to be more carefully followed, and two of these, especially, guide us in practical directions. One of them points the way to early references, which at the best are scanty and difficult of access, but which tell quite accurately what armor could do and how the early masters gained their results, a path opened up delightfully for us by M. Ch. Buttin [1] in his studies of early armor of proof. Following the second path we can actually test pieces of ancient armor and then compare the results with ballistic studies on modern “armor plate” : continuing this comparison we can then submit the old material to metallurgical examination, chemical and physical (including microscopical), and thereby gain definite information as to how the ancient steel was produced.

From early records we can clearly show that armor yielded excellent results in its day, and that during many centuries it was sought eagerly by soldiers of all classes. We learn that the prince, no less than the peasant, was quite willing to bear the discomfort of wearing it, under all conditions, even in the heat of the desert. Indirectly we know that had it not been useful it would not have appeared in numbers in every European field of battle from early times until the epoch of Napoleon. Moreover, we discover that it was used not by adults merely, but by young as well, for many suits of armor are preserved which were made for children.[2] So important, indeed, was armor in the history of from 1400 to 1700 that by its means we could still give a convincing summary of the cultural and artistic changes which took place in European civilization if all other sources of human knowledge were wiped away. [3]

The reason for the present lack of information as to the practical nature of armor is not far to seek. Little was written systematically upon this theme in olden times, and later, when armor disappeared from general use, little was remembered about it. That it would again appear as part of the regular equipment of a soldier seemed to nearly everyone a possibility infinitely remote; “for,” it was reasoned, “if armor were discarded even in the seventeenth century, in days of primitive gunpowder, how could any form of armor reappear in warfare when high explosives were used?” Hence the field of the practical nature of helmets and body armor was abandoned to an occasional antiquarian. Nevertheless, as in so many other phases of the Great War, armor did reappear in use, and thereupon there arose at once an interest, and a very practical one, in the discarded work of the armorer. Questions were speedily raised by the general staff of every warring country as to what helmets and body armor could do in protecting the soldier, what were their best forms and how they could be most speedily prepared? It may be safely said that there was not an important collection of ancient armor in Europe which was not visited by commissions, collectively or individually, in an effort to learn from the experience of the past.

Before proceeding to the already highly developed field of modern armor, let us review briefly the work of the ancient armorer[4] from the viewpoint of its practical value. This aspect of the subject, as we have noted, is surprisingly little known, not merely to the student of recent armor but to the antiquarian as well. The modern expert, as I have found, has often the belief that ancient armor was but a semi-barbarous defense, serviceable only against arrows, slings and swords. The antiquarian, on the other hand, is apt to forget that its primary virtue was serviceability and that the keenest minds had studied it from this standpoint from the earliest times.

Let us now attempt to answer several questions:

(A) What kinds of armor were early used?

(B) Was armor actually an important means of saving life and limb?

(C) How was it made?

(D) How was it tested?

(E) How heavy, irksome and even dangerous was it to wear?

(F) What in summary was its use in later times but prior to the Great War?

(A) What kinds of armor were early used?

Let us refer to Fig. 1, which illustrates the various types of armor used in Europe during a thousand years. In early times we see a jacket of padded hide discarded in favor of a coat of scales; and this in turn give place to a garment of ring or chain mail worn over a padded costume. Chain mail more or less complete was used for centuries, it was worn, not uncommonly indeed, down to colonial days in America, but nearly always more or less enclosed in armor of plate.

Plate armor was most elaborately developed in the epoch of Columbus, when the knight and his horse, Fig. 2, became almost invulnerable. By Puritan times armor had become reduced to little more than corselet and headpiece. Leathern armor then reappeared in use and the soldier’s leathern coat and heavy leg-gear were practically of the same defensive value as in the earliest time.

(B) Was armor actually an important means of saving life and limb?

Assuredly yes. Upon this point the evidence is definite. No well-made armor could have failed to preserve its wearer not merely from a very large percentage of thrusts of arrows, bolts, lances, swords and daggers, but from blows of heavy impact, given, e.g., by military hammers, flails, maces, war axes; also from the firearms of the day. As token of this one may point to the evidence of ancient and formidable injuries which numerous specimens of armor exhibit today; and one may even affirm that there was scarcely a famous soldier in those days who did not owe his life, directly or indirectly, to his armor. In fact, in tilts and single combats each wearer demonstrated many times the value of his defenses; thanks to them we know that such an artist in ring-duelling (champs clos} as “le bon chevalier” Jacques de Lalain,[5] withstood the heaviest blows of a combat-axe wielded by both hands of a “fearful adversary.” And we know that the blows of such an axe were trenchant indeed: its head weighed from three to five pounds; its shaft, weighing about two pounds, was over five feet long, to enable it to be swung with great effect. Can we picture, too, the thrusts which the armor of such a duellist resisted when a similar arm was used reinforced with a heavy blade or spike[6]? Chain mail, which one rolls in his hand today, wondering how so “flimsy” a material could have been a protection, was also of the greatest value. Against sword, dagger, arrow, bolt and light lance it was unquestionably proof. Indeed, no better testimony is needed as to its merits than the fact that for at least two thousand years it was worn constantly and in large numbers, in spite of the fact that its average price of purchase appears to have been greater than that of any other type of armor.[7]

A single instance may here be cited as evidence of the virtue of chain mail. At Tiberias (1187) when the crusaders were hemmed in by the Saracens, after two days of hard fighting, when most of the foot soldiers were killed or wounded, when hardly a horse in the army could carry its rider, the mail-clad knights are known to have suffered no serious casualties! Yet over a thousand of them exposed themselves constantly.

Mail, on the other hand, was not found proof to unusually heavy shocks. A stout lance or a musket ball was its bane, and the later history of mail finds it in use, as we have noted, only as a secondary defense, usually under armor of plate. Whenever it was worn it required supplemental padding to take up the shock of the blow. Ancient “documents” show what manner of quilted costume was worn under the mail, and in Fig. 3 one of these has been copied. When over this the shirt of mail is fitted (Fig. 3A), the wearer can withstand heavy blows with surprisingly little discomfort. That is to say, the mail with its padded costume becomes an elastic, springy complex or shield which deadens a blow with unexpected ease. Experiments made by the writer in this direction converted him to the faith that mail as a type of armor is by no means to be despised.

Armor of plate was a far stouter defense. Gothic armor withstood at short range the straight impact of a heavy crossbow bolt. And the ponderous armor of the late sixteenth and early seventeenth century withstood the shock of heavy bullets. Historical instances are not rare when armor saved its wearer from bullets at close range. About 1570, Strozzi, probably wearing the type of half-armor shown in Fig. 4, was hit by a musket ball at short range; he sustained no injury, his breastplate showing only the splash of molten lead; on another occasion, as he entered a breached wall, he was struck at a range so close that he was knocked down, the ball denting his armor; again, at the siege of Rochelle (1573) he was thrice struck on the arms, and he himself relates how he came off “cheaply.” [8] We also read in Brantome that in 1563, at the siege of Orleans, Dandelot was saved from a musket ball by the round shield which he carried; here the impact was so severe that he, too, was knocked down.

If we examine these old records we are surprised to find how often armor saved its wearer. His corselet, for example, saved Francis I “several times” at Pavia. At the siege of Rochelle mentioned above we learn that a certain Captain St. Martin remained uninjured after having been struck by musket balls no less than thirty times! So, too, the great Condé, armed probably after the style of Fig. 5 or 6, was saved many times by his armor; we have a contemporary note (1652) that at Port St. Antoine his cuirass was “full of dents.” And so it goes. There is no question, therefore, that armor was useful even at a time when gunpowder was in general use. Moreover, the bullet of that period was usually of large caliber; its crushing effect must have been great, and its shock formidable.

The fact is clear that had cases not been numerous in which the soldier was saved by his armor, the armor would not have been worn. Nor was the burden too great, considered from every viewpoint, if by means of his armor a particular person could be preserved. For those were days of individualism. And the personality, courage and resourcefulness of a leader would often spell the difference between the victory and the defeat of a nation. Had Marlborough been shot, whom his soldiers followed blindly, what might have been the outcome of the battles of Malplaquet, Ramillies, or Blenheim? Or was it not of the greatest importance to the French nation that Joan of Arc should be protected by armor of best possible proof? We know indeed that she was several times saved by her armor. Fancy, too, how the history of the world might have changed had the Black Prince been killed in battle; or Cromwell, or William of Orange, or Francis I or Charles V. Yet we know that all of them exposed themselves with reckless determination, and that all of them were armored by masters. One has only to visit the royal armory in Madrid today to know what such a man as Charles V thought of the practical value of armor. He was literally a specialist in its study and he provided himself with armor for every eventuality and of every weight. He graded his armor as an optician classifies his lenses; in one instance he had at least eight reinforcing pieces for a single helmet. And for tilting he did not hesitate to wear armor which would stand a supreme shock. He was a man of modest stature and proportions, yet his tilting armor in one instance weighed no less than a hundred and twenty-five pounds and his helmet alone over forty pounds!

(C) How was early armor made?

The best material used by early European armorers came from special localities, where the iron occurred in natural association, probably with chromium and nickel, thus producing an alloy of great ballistic resistance. This material, e.g., from Innsbruck or Bilbao, became a staple article of commerce during the Middle Ages; it was sold in bars or in plates; the latter had been hammered out, sometimes by hand, but usually by a trip-hammer operated by water power. (See Agricola, Georgius, De re metallica, Basel, 1546.) In making armor the armorer worked his metal sometimes hot, sometimes cold, depending upon the kind and quality of work which had to be performed. The details in making armor need here be noted only in so far as they furnish materials for comparison or contrast with the modern methods.

(D) How was armor tested ?

It is not hard to conclude that the armorer, during all periods, took practical means of showing to the purchaser of his armor that it was of good quality, or “proof.” And the early records when carefully examined bring out numerous details indicating in what way and under what conditions the testing or proving of armor took place. That it was often done on standard lines there can be no doubt. And it was occasionally carried out under particularly severe conditions. In this connection let us review a number of tests.

The earliest one accurately recorded[9] occurred during the siege of Rhodes (308-304 B. C.) when Demetrius Polyorcetes, according to Plutarch (Demetrius, Section 21), received from Cyprus two heavy iron corselets (probably breastplate only), each weighing the equivalent of thirty-eight pounds Troy. Zwilos, the armorer who made them, thereupon caused them to be tested in order to show that they were of great strength and hardness; to this end they were shot at by a catapult at a range of twenty paces. The iron resisted the shock and the head of the catapult bolt merely nicked the surface “as though with a stylos.” Thus the test was made under war conditions and it is noteworthy that the armor was not placed on racks or models but on living men. “One of the corselets was worn by Demetrius himself, the other by Alkinos of Epeiros.”

It would be interesting to know just what this test represented in terms of modern ballistics. That it was severe goes without saying, especially since the bolt of a catapult, which represented the siege artillery of that day, had a weight which would have been hard to stop (perhaps as much as ten ounces, i.e., double the weight of a heavy war-bolt of a windlass crossbow). In modern terms it is even fair to assume that had the breastplates in question been of low carbon steel, and they probably were, they would have stopped a machine gun bullet at about three hundred yards. It is surprising, therefore, that the earliest instance of a military proof of body armor recorded, occurring some twenty-three hundred years ago, should have given essentially modern results, but, naturally, at the cost of greater weight.

Detailed records of proving European armor do not next occur until the fourteenth century. But from this it does not follow that during the intervening time there were made no efforts to prove the armor and to standardize the tests. We incline rather to the belief that each purchaser of armor had a clear idea of the degree of resistance his shirt of mail and his iron headpiece should offer, and that even in his tests he did not fail to make use of crossbow, lance and sword. Unfortunately we do not know from actual experiment, ancient or modern, what a good shirt of mail (weighing, say twenty pounds) will resist, when each link is riveted and hardened, but it was evidently of greater strength than modern shirts of mail unriveted, which, of about equal weight, are claimed by their makers to resist service-revolver ammunition at less than fifty yards. In general we know that early armor of this type was often tried out by the chopping cut (estramafon) of a sword, and that a similar test was used throughout Europe down to the seventeenth century. (Fide Gaya, 1623.) The thrust of a heavy poignard was also a severe test. In this connection I recall in Paris many years ago discussing the proof of fifteenth-century Italian armor with M. V. R. Bachereau, the well-known antiquary of ancient arms: “That armor is indestructible,” declared M. Bachereau, and “it would surprise you to know how flinty hard its surface is.” He told me he had taken from a vitrine a headpiece hall-marked by the great Milanese maker, Antonio di Missaglia, and placed it on a block. He had then struck it with all his strength with a heavy-bladed dagger; the headpiece hardly showed where the point had struck. This incident I mention since it is the only one in which I have known an early helmet to be given a practical test. Perhaps it is not to be wondered at, for museums and collectors can hardly be expected to permit some of their most valuable specimens to be used in ballistic or similar tests!

As early as 1340 we have records that armor of two degrees of strength was in use, known respectively as “proof” and the “half proof.” The former would withstand the bolt of a heavy crossbow, which was set with a windlass, the latter only the arrow of the war-bow and the bolt of the small crossbow. Two expressions to distinguish the strength of armor date also from this time (Italy and Savoy), armor “proof to every thrust” (de toute botte) applying apparently to plate armor, and “to thrust broken” (botte cassee) in the sense that the armor yielded and thus broke the thrust. The latter armor, including apparently chain mail and armor of small plates or scales (jazerans, from Spanish Jazerino = Algerian) was apparently the more highly prized; and it was more costly (one fifth or more).

Records of proving armor become frequent during the fifteenth century. And by this time measures appear to have been taken to standardize the test. Many cities had their stamps (poincons} and made use of them in certifying to the excellence of their armor. Thus numerous helmets and breastplates in our museums bear the proof mark of Nuremberg (demi-eagle and fesse), Venice (lion of St. Mark), Augsburg (pine-cone); together in some cases with the individual mark of the maker. Occasionally not only is one piece of the armor thus marked but nearly every piece, including gauntlets and leg pieces. And in extremely rare cases (to show what store was set by tests of this kind) the same piece was hall-marked at many points. A Milanese armet in my collection bears the pomfon of proof on its back on the left side, on the right cheek and on the left, and the mark of “double proof” near the back on its right side. The double mark mentioned is believed to record a test of much greater strength. These tests were made with special crossbows and special bolts or quarrels; and tests of this nature were still in force well into the sixteenth century.[10] Occasionally we read of armor which was tested in the presence of the purchaser, who brought with him special bolts and a “good windlass crossbow” to make sure that the proof was severe. This test, we may add, is not easily compared with a modern one, but it was fairly searching, for the projectile was heavy (four or five ounces), revolved in flight, and its point was well adapted to punching holes through metal plates. Such a bolt flew with an initial velocity of about 300 feet a second (writer’s estimate) and it attained a distance of 400 to 500 yards; at 60 yards it would penetrate a wooden plank three fourths of an inch thick.[11]

Early in the sixteenth century guns became used in large numbers and shattered much armor of “proof.” Thus in 1517, Ariosto advised the soldier to send his armor and sword back to the forge and to adopt the musket or arquebus. (“Orlando furioso” Canto IX, stanza 29.) So, too, we find in 1523 a note in Montluc’s “Commentaries” (Ed. 1821, Petitot, Vol. I, page 342) which deplores the death of “so many brave and valiant men, often at the hand of the most cowardly and timid, who did not dare to meet face to face the men whom they shot down with their miserable bullets!” Hence it came about that the conditions of proving armor were changed, and that by about the middle of the sixteenth century armor was made heavier, and the terms “proof” and “half proof” acquired a new significance, suits of the former type resisting the (war) musket, the latter the lighter firearms, including pistols. Sometimes a suit of armor was made up partly of “proof” (front of helmet, breastplate and upper thigh defenses and circular shield) and partly of “half proof” (backplate, arm defenses [12]). To compensate for the increase of the weight of the breastplate it was even advocated that no armor for the back be worn, on the ground that it was unnecessary, and that its absence would discourage cavalry from turning its back to the enemy. [13]

For the rest it becomes clear that testing by firearms was an important factor in the decadence of armor, and that, little by little, each plate grew heavier, till at length the entire panoply became literally unbearable. During this time the competition became intense between the armorer and the gun-maker, whose clients added insult to injury by rejecting a musket if it did not shatter the armor, and rejecting the armor if it did not resist the musket. “Of course my fine armor failed,” complained the armorer Colombo of Brescia (1574), “when my patron used an inch charge of powder!” And we can understand how the earlier armor, elegant in its lines, with its delicately adjusted curves, grooves and angles, designed especially to deflect the crossbow bolt, should in time give place to armor, solid and compact, rounded in contour. But even then the proof demanded by the wearer of the armor mounted always higher (“high-proof,” “caliber proof,” “musket proof”) so the armorer was obliged constantly to resort to new devices. He knew little of the metallurgy of steel), so he did not experiment with ballistic alloys; he did, however, like Vulcano of Brescia, strengthen the “fiber” of his heavy plates by the laborious process of hammering them out cold and by using various processes of tempering them; but in general he had either to make his armor of fewer and heavier pieces, or to use the earlier designed reinforcing plates by means of which a patron who had complete armor could strengthen his breastplate or headpiece and at the same time reduce the total weight of his equipment by discarding other pieces, according to his actual need. The result, however, tended ever in the same direction, the armor became far too heavy; and its wearer began to complain that he had become little more than a “living anvil,”[14] for he was so burdened with his harness that his value in active combat became small. Thus, even if dismounted, he could hardly get back into his saddle. [15] (ffoulkes, “The Armorer and his Craft,” page 117.) In the end, throughout the seventeenth century, the best the armorer could do was to keep his clients well mounted at the head of their troops where their presence and beaux gestes could inspire their men to further efforts. And they certainly found their way into the thick of the battle, for we recall that in those days princes and generals exposed themselves in a fashion which would seem to modern tactics little less than criminal. But while the opposing heroes rarely met in single combat in Homeric fashion, it is none the less true that they had often the opportunity of recognizing one another and at close range during the fortunes of battle. Many suits of armor of the latest period (say from 1560 to 1750) bear dents of bullets; certain of these are scars of warfare, but they are usually testing marks. Cf. Figs. 4-6. They were made prior to the finishing of the armor, for they are still apt to be below a russeted, blued or gilded surface, or even to form centers for etched or engraved ornaments. One, two or three of these marks may appear on the breastplate (sometimes at points concealed by large shoulder guards, as in the armor shown in Fig. 6), one on the backplate, one on each hip defense, one on each shoulder. The proof balls may have been shot in the presence of the person who had ordered the armor, at the time the plates were fitted to him but before they were filed and finished. In such a case the bullet was of lead weighing about one ounce, and the charge of black powder was sufficient to cover the bullet when held in the palm of the hand. (Cf. 1667 “Memorial of the Verney Family,” IV, page 30, and the Gaya Reprint, by ffoulkes, Clarendon Press, 1911, page 30). There appears no record as to the distance at which the shot was fired nor the firearm employed, nor yet the mode of wadding, although these are factors which influenced the test vastly. The ancient armorer, we fear, like makers of certain types of modern armor, was apt to gloss over details. Thus, he did not care to have the test made with cartridges specially prepared at the house of his client. “In general,” wrote Pistofilo, “Heaven protect me from the musket which has been specially loaded at home!”, and other writers comment upon the superior force of the first shot from a gun, a condition which, in days of poorly made powder, one may well understand, for a gun barrel would speedily have become clogged with carbon.

In all tests a serious effort appears to have been made by early experimenters to find the best results which could be had in proportioning the weights of powder and ball. And they seem to have decided, as Cellini narrates in his autobiography, that the best penetration could be had when the powder weighed not more than one fifth of the bullet, a proportion, by the way, which has been confirmed repeatedly in later days even for the last rifle of the French Government using black powder. Indeed, it may truly be said that the early authorities were dealing with problems of explosives in a very modern way. Experiments were in full swing with noiseless powder, and Cellini, for example, tells (“Vita” Lib. I, Cap. VII) how by its means he was able in his hunting to keep from frightening away the most wary birds. Also shapes of bullets were being considered with up-to-date precision and there are records of models, including conical ones, which should have given excellent results. These followed the use of long projectiles shaped like crossbow bolts. Then, too, metals other than lead were employed experimentally. Iron, tin and copper were used, the last especially having a certain vogue (Admiral Coligny, by the way, was shot with copper bullets on the eve of his death). Clearly, too, the experts had ever before them the need of inventing armor-piercing bullets, and they came very close to solving their problem when they used steel bullets dipped in lead. But then, as in so many other instances, instead of following an excellent scent, they veered off in unscientific directions, as when they attempted to associate special metals with special grades of victims: thus, “only a bullet of gold could be used to cause the death of an emperor.” And gun wads should contain cabalistic formulae.*

(E) How heavy, irksome and even dangerous was armor to wear?

If one examines Table I, he may compare the weights of various kinds of body armor and helmets. Chain armor was almost as light again as plate armor. [16] Suits of plate, it will be seen, did not increase notably in weight during the century from 1450 to 1550; but during the century following they became heavier by perhaps 20 per cent. Tilting armor naturally attained extraordinary weight, since its wearer needed extreme protection and for only a short period, thus a harness of a hundred and twenty-five pounds might be tolerated if it were to be taken off again within half an hour. Helmets, of which the various kinds are pictured in Fig. 8, may be divided conveniently into four groups, light, medium, heavy and very heavy. Light headpieces average three pounds in weight and include early bassinets, certain burganets, morions and cabassets, iron hats and hat-linings. Medium helmets weighing about six pounds occur in visored bassinets, salades, barbutes, armets and certain burganets. Heavy helmets weigh ten pounds, e.g., closed burganets and tilting armets. And very heavy helmets, say of twenty pounds, are represented by heaumes and siege burganets. The last-named headpieces would probably stand a good ballistic test with the most recent firearms. In their day they were proof to shot of large caliber, which were justly reckoned as most dangerous in crushing armor; they are said to have withstood a quarter pound ball, and even a one pounder when largely spent. In the matter of the discomfort of wearing armor, there can be no question that it was always irksome. But soldiers became used to it and the literature of the subject shows that they rarely complained of its burden until late in the sixteenth century. In earlier times the hardened wearer used it in active service all day long. If exceptionally active he could vault into his saddle (or over it) in full panoply, weighing, say fifty-five pounds, and while his horse was galloping he could jump to the ground without using stirrups;* he could throw himself on his back at full length and gain his feet in hardly more than double the time he could do it unarmed, the last a result which I have confirmed by actual experiment. But these things can be done only when armor fits the individual and is worn over the kind of costume adapted to it, with the necessary “points” for supporting the elements of the suit. See Figs.9 and 9A. In fact, under these conditions armor is worn with surprisingly little discomfort. I can bear witness that a suit of half-armor weighing thirty-five pounds can be worn for a stretch of three hours, and by a novice, without extraordinary fatigue or subsequent lameness.

It was only from the latter part of the sixteenth century, when armor weighed over sixty pounds that we find the old-time soldier grumbling about his equipment. Pikemen would have none of it, “many throw it away,” complained Saulx-Tavannes and Pistifilo. Horsemen would put it on only at the last moment; and Montaigne (1587, Essays) deplores “the vicious habits of his times and full of weakness to take up one’s armor only at the call of extreme necessity, and to get rid of it at the very moment when the danger appears to have passed, for this gives rise to much disorder” . . . “the old fashion was better which insured that each soldier had on a part of his armor all the time.” Still the fashion was spreading that the armor was to be carried as part of the equipment of the camp, rather than of the individual. Thus Saulx-Tavannes pleads that “captains and soldiers in close touch with the enemy should accustom themselves to carry their armor without confiding it to their servants in order to avoid the confusion which appears when there is need to look up their luggage.”

But the fact of the matter was that so far as long marching service in war was concerned armor had become a physiological failure. Not merely was the wearer rendered inactive when wearing it, but in time he became actually crippled or “broken” by its use. A droll writer, whose stories were read everywhere, commented audibly upon the shortcomings of men who had worn armor. Brantome declared that he himself had known them to be spent at thirty years. Montaigne says that “today (1587) the officer is so heavily armed that by the time he becomes thirty-five his shoulders are completely humpbacked.” And La Noue (1587) repeats the same story. [17] The result of this was, according to Buttin, that “officers and soldiers not wishing to be crippled by thirty-five threw away their armor as often as possible, to the detriment of their discipline and to the advancement of much improvised quarrelling.” This marked an important if not a final stage in the armorer’s decline.

(F) What in summary was the use of armor in later times, but prior to the Great War?

In the preceding paragraphs we have seen that from the late sixteenth century the soldier complained bitterly of the weight of his armor: it crippled him, it prevented him from taking an active part in battle, and he threw it aside if he could. In spite of all this he admitted that armor was an extraordinary means of protection. It was for this reason that it did not disappear at the first flash of a gun, as is popularly believed, but remained in use for centuries while powder was being developed, and when it was in general use in warfare. In fact at the time of the highest development of armor at the end of the fifteenth century hand-guns had already been in use for a century; and there is no doubt that armor was used most frequently from the middle of the sixteenth to the middle of the seventeenth centuries when guns and pistols were in common use. At that time, indeed, powder had been notably improved in quality and already many “modern” devices had been invented. (See Table II.) Hence we have reason to believe that the general disuse of armor was not due entirely to the failure of armor, in spite of its weight, to resist firearms, but to other causes as well. Here should be mentioned especially those changes in military tactics which were taking place at a time when armor was declining. Thus during the Thirty Years’ War (which ended in 1648) the Swedes, especially, built up a military system wherein it became necessary for manoeuvring armies to cover long distances in short time, a system which alone might have encouraged the infantry to throw away its armor, whether light or heavy. In fact I am inclined to believe that this factor is far more important in the disappearance of body defenses than is usually reckoned. For so soon as armor began to drop out of use it became unfashionable, then unpopular and in the end discredited. That it could still have been used to good purposes seems none the less clear if we examine attentively the comments of certain masters of war during the eighteenth century and there is no better case in point than that of Marshal Saxe (1750) who goes out of his way to recommend the use of armor, declaring that it is the more needed since in his experience casualties were caused in greater number by swords, lances and spent balls than by projectiles of high velocity. And we infer that such opinions were not exceptional since we find that suits of armor, lacking defenses for the lower legs, were worn in number up to the time of the French Revolution. Even in America we find such armor in use at the time of the French and Indian War and in rare cases during the Revolution. Lord Amherst, for example, in his Canadian campaign (1758-1760) is pictured thus armed, wearing even hip defenses, Fig. 10. Kosciuszko, also, wore armor and probably brought it to this country; and we have reason to believe that Rochambeau wore his siege armor at Yorktown (1781), for he is described by Joel Barlow as in “gleaming steel arrayed.” And Paul Jones, while not in half-armor, wore a corselet under his coat during the fight with the Serapis, according to his fellow-Scotsman, Hyslop. (See Bull. Met. Mus. Art, 1912, Vol. VII, pages 26-28.) Possibly, the latest armor worn as a more or less complete suit appears in Reynolds’ portrait of the Marquis of Townshend, and dates late in the eighteenth century; but we are not sure of the date of this harness, for it may have been merely a form of ceremonial costume which the painter adapted, or it may have been of considerably earlier date, e.g., worn at Fontenoy, Dettingen or Culloden. During this late period part of the armor it appears was designed to resist bullets of fairly high velocity, shot often from rifled barrels and by good black powder. The bullets, however, had not a great range, rarely as much as seven hundred yards, and with great individual variation; but they were usually of large caliber and proportionally more destructive than those in present use. Thus bullets of the Revolutionary musket weighed about fourteen to the pound (= 500 grains), which is heavier by 50 to 100 per cent than the present rifle ball (Spitzer). (The latest Mauser weighs 227 grains.) [19]

Armor of this kind showed, for one thing, that there was no evident ground for the common belief that the severe shock of a projectile against armor would in itself be fatal to the wearer even when the armor remained unbroken. In fact, we shall see that armor which resists a machine gun, say at fifty yards, did not cause its wearer grave discomfort from the impact even of a series of projectiles. In a word, from the study of the history of armor one can find no reason why it could not be used under certain modern conditions: hence it follows that if armor were required in actual warfare, there would be no need of developing a new system of wearing armor. We should advance merely a step further in its historical development.

There is no question, then, that armor passed out of general use not at once but gradually. Thus after the year 1620, leg armor rarely appeared and defenses of the hips and thighs are uncommon from about 1670. Defenses for the arms were abandoned piece by piece somewhat later, although complete arms continued to be used for about a century in ceremonial armor, i.e., as worn by highest officers. For a long time the neckplate or gorget was retained as part of the regular equipment and it even became exaggerated in size; but it finally became so small that its function as a defense had practically disappeared. As shown in portraits of Colonial and Revolutionary times, it was little more than an ornament which was attached to the officer’s neck by a ribbon and usually bore his regimental number. See Figs. 11 and 12. The corselet and helmet have remained ever in use in certain state guards or cavalry regiments. These plates were made of low carbon tool-steel and are fairly resistant even to modern explosives.

A heavy corselet (forty-one pounds), probably of the time of Napoleon, was recently tested by Captain Roy S. Tinney (National Service Magazine, January, 1918, pages 395-403) and gave good results; it resisted in turn Craig ammunition .30, 40 to 20 with muzzle velocity 1,970 foot seconds; at 100 yards 1,553 foot-pound blow; a Winchester .30, 30, 170, of 1,522 foot pounds; a Sharp’s rifle of .45-90, 300, at 100 yards (muzzle velocity 2,644 foot seconds); and finally the 303 Savage firing a 195-grain bullet having muzzle velocity of 1,658 foot seconds. In a word, such a corselet resisted projectiles which were scarcely inferior to those in use on present battlefields.[20] With this test in mind, we may well believe the early statements that the cuirass of the guardsman played an important part in bodily protection during the eighteenth and nineteenth centuries. During the eighteenth century, we recall that its use was fairly constant for cavalry (for the highest officers, especially, when parts of it, at least, degenerated into a ceremonial costume). And in the early nineteenth century, the corselet and headpiece appeared in great numbers in European armies. For one thing, Napoleon the Great favored their use. And there still exists his order to Requier, chief of the artillery museum of Paris, to send post-haste to Tilsit (1808) the corselets and casques which had been made for himself and the Prince of Wagram. There is no question, also, that armor was worn at a very late date in sieges and in naval warfare. Thus heavy helmets and shields of various forms were used during the eighteenth and nineteenth centuries, especially for the defense of sappers. In Fig. 13 is pictured one of the heavy leathern headpieces worn by sappers (and possibly by firemen), 1750-1800; specimen now in the Tower of London. In Fig. 14 appears a heavy helmet of this type drawn from a specimen in the Tower of London; its weight is over nineteen pounds and it dates from about 1848, judging at least from Raffet’s picture of the siege of Rome in this year, when sappers are shown wearing helmets of this type. Perhaps, too, we should here mention the numerous types of metal “helmets” which have appeared as headgear for infantry and cavalry during the late eighteenth and throughout the nineteenth century which were of little value save ornamental, e.g., the eagle headpiece of the fugitive German emperor.

In the Orient armor was used practically up to our own time and is probably still worn in out-of-the-way localities in Persia and India, more as a ceremonial costume, perhaps, than for use in warfare. Moreover, we know that the Japanese wore armor regularly until about 1870, and fairly good armor it was. Chain mail reappears in the East with curious persistency. As late as the Younghusband Expedition to Thibet (1903) cases occurred where natives were captured whose costume, reinforced with chain mail, had successfully resisted the bayonet thrusts of the English. Hardly earlier than this, chain mail appears to have been worn in the region of the Caucasus. Similarly, we note that coats of mail are still worn secretly wherever danger is dreaded from personal attacks, especially by sword or knife. The writer learns from good authority that a well-known armorer in Paris derived, until about 1908, a substantial part of his income from making shirts of chain mail which were shipped to South America and Africa for actual service.

To trace in further detail the use of armor in relatively recent times: It is known that breastplates were worn more or less frequently during the American Civil War. In the museum in Richmond, there is preserved such a “suit” of armor, Fig. 15, which at the time of the siege was taken from a dead soldier in one of the trenches. He was shot in the side or back, for the breastplate, it appears, was not penetrated. This armor was of northern origin. Further inquiry shows that a factory for the making of such defenses was established at New Haven about 1862. The metal employed was a mild steel, .057 inch thick, and the “suit” weighed about seven and one half pounds. While no tests of this armor are available,[18] we estimate from the thickness of its metal, assuming that it is a “mild” steel, that it would have stopped a 230-grain pistol ball traveling at the rate of 500 foot seconds.

During the Franco-Prussian War several types of armor were used to a limited degree. The heavy corselet appeared, also the horseman’s helmet. We have occasional reference to the use of a very heavy helmet in the trenches and also of varied types of armored waistcoats. One of these, manufactured in Paris, is shown in Fig. 16. This specimen is made up of small rectangular plates of low carbon steel and riveted to canvas. The entire defense weighs about five pounds and could be worn with a reasonable degree of comfort. It does not resist a 230-grain pistol ball at 650 foot seconds, and from its behavior in this test, one doubts whether it would have resisted a similar bullet at a velocity greater than 300 foot seconds. Its value, therefore, lay in protecting its wearer only from spent balls or splinters. Ballistically, it had much less strength than the light-weight shrapnel helmet in present use in the American Army.

In all later wars, armor appears to have been used sporadically, sometimes as body defenses, sometimes as helmets, sometimes again in the form of shields which were either carried by the soldier or pushed in front of him. It was due to small shields of the latter type that the Japanese were able to take some of the most difficult outposts of Port Arthur. Also, in the Boer War armor appears to have been used. Thus in the siege of Ladysmith, helmets were used which are said to have been proof against machine guns. They were clumsy affairs and heavy, and were not firmly attached to the head. No details of these helmets have been recorded nor have we been able to secure photographs of them. From an officer (Lieutenant R. Miller of the Imperial Light Horse) who was present at the siege, the writer learned that the defenses in question were crudely made and were only moderately effective.

The most convincing historical instance of the use of helmets and body armor against modern ammunition dates from 1880. This was in the case of the Australian bandit, Ned Kelly, who long owed his freedom to the fact that he wore armor (Fig. 17). This, it appears, he had improvised; it was the “work of some skilled local artisan.” It is said to have been made out of old plowshares, beaten into plates one quarter of an inch thick. It was badly fashioned and extremely heavy, weighing ninety-seven pounds, but it covered the body completely. On various occasions it was badly “shot up” but not penetrated. Its wearer was captured after a several months’ chase and then only after he had been shot in the legs. To give one an idea of the efficacy of this armor against Martini rifles at close range, we insert the following quotations from the official account of this case written by one of the attacking party.

“I have no hesitation in stating,” writes Superintendent Hare, “that had the man been without armor when we first attacked . . and could have taken proper aim, not one of us would have escaped being shot. He was obliged to hold the rifle at arm’s length to get anything of a sight.” “His armor included a great headpiece which was like an iron pot which rested on the wearer’s shoulders and completely protected the throat. The outlaw as he advanced toward the policemen had taken the precaution to conceal his armor under a long gray overcoat.” “The first policeman closed in upon him and a strange fight began. The soft Martini-Henry bullets dinted his armor but did not penetrate and he coolly returned the fire.” “It appeared as if he were a fiend with a charmed life.” “For one half-hour this strange combat lasted.” “Then one of the party rushed in and shot the outlaw in the leg, then sprang upon him and disarmed him.”

This instance of the use of armor against modern gunfire is of especial interest since it shows that an armored man could stand in front of a squad of riflemen, even at close range, and be reasonably immune. He could even kill them all, as Superintendent Hare admits, if he were a skillful marksman.

From the time of Kelly’s practical “experiments” up to 1914 the matter of body armor had not been held altogether in abeyance. And he who follows the literature of the subject will be surprised to find how many types of “bullet-proof” devices have been invented. A breastplate known by the name of its promoter, Rowe, apparently patented, was experimented with extensively prior to the year 1901. It gave results so promising that it attracted the personal interest and support of the German emperor. Another body defense known as the corselet Loris was also “tried out” about this time; its inventor demonstrated its effectiveness, if I am correctly informed, in various theatres in France. So, too, a bullet-proof waistcoat was designed by Casimir Zeglin and worn about 1897 in spectacular tests in a New York theatre. And in London similar demonstrations, more or less serious, were made by inventors, whose results, by the way, Sir Hiram Maxim accurately followed up, he himself suggesting a certain type of high alloy plates (containing tungsten) for their armor.

Even chain mail was developed by these experimenters. Thus in the military retrospective exhibition of 1889 in Paris types of mail were shown which were “proof” to dagger thrust and to the lead ball (433 inch) of a service revolver. The former mail was made up in alternate rows of links solid and open (i.e., formed so that the tips of the wire merely butted together), made of tempered spring-steel ; the better quality of mail had its links fused or riveted.

About the year 1900, in fact, a dozen or more types of armor were being exploited. A well-known establishment at St. Etienne was then advertising a light breastplate proof to service revolver. A cuirass made by Alphonse Payot of La Rochelle, Savoie, was in the market, and one devised by Ernest Benedetti was tried out in Rome (1901) before a military commission and was given a favorable report. And at that time military writers were impressed with the necessity of reconsidering the armor problem. “If out of a thousand soldiers not one can reach even an improvised trench when it is defended by machine guns we must arrive at the adoption of some kind of a portable defense,” writes Captain Danritt (“La Guerre de Demain” page 600). Ch. Buttin notes at that time ( 1901, “Les Armures a Fepreuve” Annecy, pages 99-100) that the “question of proof, far from being a dead issue, is the order of the day,” and that “nothing is more sure than that science has never said its last word. And perhaps there will be found, even if it has not already been found, a process of making again in a scientific way that which the earlier armorers were unable to produce in their day, in spite of the superiority of their workmanship, a corselet, light and truly proof, this time to the test of an armor piercing bullet!”

[1] “Notes sur les armures a I’epreuve.” Annecy, 1901, 100 pp.

[2] See also Ch. ffoulkes, “The Armorer and his Craft.” Methuen, London, 1912.

[3] That this statement may be given more definitely we point out that arms and armor unquestionably furnish the best expression of the art and the science of the metal worker of the Middle Ages and of the Renaissance: Armor includes in its decoration, gilding, silvering, tinning, damascene, niello, even jewel-setting: its ornamental designs explain to us stages in the development of religious and civil customs, including pageants and sports, not forgetting falconry. It furnished also an important medium for the art of painting: its enriched variants copy for us types of secular apparel of each period; by means of etching it pictures the stuff of which the costumes were made; it also offered an excellent medium for ornament, with lettering and borders. In its mounting it summarizes the textile art of various periods: here appear tissues from the commonest to the most costly, including galloon and fringes, and with these are adequate materials for the study of the art of the leather worker. The size of armor gives us, finally, convincing data as to the state of physical development among the men of many nations.

[4] For critical help in preparing this section I am greatly indebted to Mr. Charles W. Gould.

[5] Lefevre de Saint-Remy, “Chronique de Jacques de Lalain’ [1421-1453], published in 1842, Pantheon litter aire.

[6] A shirt of mail in the collection of the Metropolitan Museum of Art contains a quarter of a million hand-made and tempered rings, each carefully formed and each separately riveted. If one estimates that a skilful armorer might make and weave together two hundred and fifty of these links in a day, it is easy to see that this mail would have cost its maker, working every day, nearly three years’ work, a low estimate, we believe, for making this particular mail. Such a shirt would therefore have cost its purchaser in round figures, at modern prices, six thousand dollars, allowing the maker six dollars a day for a thousand days! [Editorial note: $6000 in 1914 dollars is approximately $146,275 in 2017 dollars.]

[7] 1898, Oman, Ch., “A History of the Art of War.” Methuen, London, pp. 323 et seq. “To their [the Moslems’] great surprise they found that very few of the knights had been seriously hurt; their mail shirts had protected them so well from the arrow shower that few were badly wounded and hardly any slain. . . .”

[8] Brantome, “Courronels francois,” Liv. II. Ch. I. Edit. Elzv., Vol. VII, p. 44. In footnote p. 53, as quoted by Buttin, “voila comme j’en eschappy a bon marche.”

[9] Crude tests of armor by sword, spear or arrow are doubtless as old as history itself. Here should be mentioned David’s testing the armor which Saul offered him (about B. C. 1015). I Samuel, xvii, 38, 39. “And Saul armed David with his armor and he put a helmet of brass upon his head: also he armed him [by providing him] with a coat of mail. 39. And David girded [drew] his sword upon his armor and he assayed to go [to let go or strike at it] ; for he had not proved it. And David said unto Saul, I cannot go with these, for I have not proved them [shown that they were not proof]. And David put them off him [put them away from him].”

[10] Crossbows were not discarded in the French army until 1566, when, indeed, many soldiers still preferred them to muskets; and in England the use of the musket did not become obligatory until 1596.

[11] See Payne-Galway, Sir Ralph, “The Crossbow, Medieval and Modern, Military and Sporting.” 1903, London, XXII, p. 328.

[12] In instances all parts were designated as half proof, including even the groin-plate (brayette). v. Catalogue of the armory of the Dukes of Lorraine, 1629.

[13] A similar reason for abandoning the backplate was recommended by Alexander the Great. (Rollin, “De la science milttaire” liv. XXV, 3.)

[14] La Noue in his “Discours pohtiques et mihtaires” translated by “E. A.,” 1587, writes on page 185, quoted by ffoulkes, “For where they had some reason in respect to the violence of harquebuzes and dagges (muskets and pistols) to make their armor thicker and of better proofe than before, they have now so farre exceeded, that most of them have laden themselves with stithies (anvils) in view of clothing their bodies with armour.”

[15] Thus, Gaspard de Saulx-Tavannes, in his memoirs (“Collection des Mem. relativ. a l’histoire de France” Paris, Didier et Cie., 1866), notes “that it is impossible for captains in their heavy casques and cuirasses to strike many times, as is their duty. If one who commands wishes the help of a casque and breastplate, proof to the musket ball, he must take them only at the moment he charges.”

[16] This difference in weight is, however, deceptive; for with chain mail a much heavier supporting costume was worn.

[17] “Discours politiques et militaires” “Neither was their armor heavie (those days) but that they might wel bear it 24 hours, while those that are now worne are so waightie that the peiz of them will benumme a Gentleman’s shoulders of 35 years of age.”

[18] Since this was written Miss Helen Gibbs, curator of the Museum of the Virginia Military Institute, has very kindly forwarded to the writer a hip-guard belonging to this body shield. A test shows that it will resist a 45 Colt-revolver bullet of 2OO grains at about 700 foot seconds velocity. A second test was made with standard ammunition (800 foot seconds), 23O-grain jacketed bullet from the 45 automatic: one shot failed to penetrate at ten feet, two penetrated but without splintering the metal. The body shield was, accordingly, a surprisingly good one for its period before the development of higher ballistic alloys. Again, thanks to General Nathaniel Wales of Jamaica Plain, Mass., I have just received very interesting data regarding this “steel vest” of 1862. He states that “it was worn more often than we had any idea of, but many officers felt they should not be protected better than their men, consequently those who wore the armor did not advertise it.” . . . Thus “two of as brave officers as I ever knew wore it, my colonel . . . and my major who was killed, a bullet grazing the bottom edge of the vest and passing through his body.” He states also that his life was saved by it at Antietam (September 17, 1862). Quoting his letter: “I had been presented with a steel vest by my father when I left Massachusetts, but I left it in Washington. When I entered the fight a brother officer, who was wounded, insisted on my putting on his steel vest. . . . When I advanced [in the open to meet a rebel charge in the twenty-first Massachusetts regiment] a bullet [evidently at close range] struck me just below the heart . . . knocking me down. Getting on my feet I walked back to where General Ferrero was lying behind a ledge. As I passed him he said, ‘Where are you going, adjutant?’ I replied, ‘I am hit, sir.’ ‘Where?’ I pointed to the hole in my coat and he said, ‘You had better go to the rear.’ I sat down remarking, ‘Til see how badly I am hurt.’ It was not until I grasped the cartridge-box belt to unclasp it that I realized I was wearing the steel vest. The convex side of the dent had cut through vest, shirt and undershirt making a small cut in the flesh. It was considerably swollen and for ten days or a fortnight I was unable to draw a long breath.” The drawing of the armor which accompanies the notes of General Wales shows that his escape was the luckier since the bullet struck the breastplate very close to the point where four plates came together, a region of structural weakness in armor of this type, for the free corners of the plates are held together only by rivets.

[19] Editorial note: The M855 5.56x45mm round weighs just 62 grains, so it’s just over a quarter as heavy as the old Mauser round — and it is, needless to say, much smaller than the 500 grain rounds of centuries past, which are like miniature cannonballs in comparison. Of additional note is the notion that the M855 is generally considered ineffective at distances past 500 yards, so it may perhaps be considered inferior to the Mauser in this respect as well, yet, due to its hardened steel penetrator, the M855 is very effective at penetrating steel armor and lesser barriers.

[20] Editorial note: In many respects, this holds true to the present day.