A Short History of the Ballistic Steel Helmet
Although the first steel helmet is lost to history, it was the Romans who were first to make wide use of steel helmets in battle, and they were certainly the first to make those steel helmets iconic. Roman helmets, which were used alongside bronze helmets of similar design, were of sophisticated metallurgical composition — their helmets were generally either carburized or made of a reasonably high-quality medium-carbon steel alloy, though not necessarily quenched.
But to write the history of the steel helmet itself from the Roman era would fill an entire book. The history of the ballistic steel helmet is a much shorter story.
We can begin by simply noting that the plate armor and helmets of the 14th-16th centuries were increasingly designed to withstand ballistic impacts, and, on that account, grew thick and heavy over time. Some of the helmets of that era weighed more than twenty pounds — and, although that’s an admittedly extreme example, and helmets that heavy were very rare, helmets of more than five pounds were downright common.
Not surprisingly, steel body armor was also growing very thick and very heavy. In 1587, French military theorist and famed essayist Michel de Montaigne noted that “today the officer is so heavily armed that by the time he becomes thirty-five his shoulders are completely humpbacked.” In a separate account of roughly the same period, Montaigne noted that “Alexander, the most adventurous captain that ever was, very seldom wore armour, and such amongst us as slight it, do not by that much harm to the main concern; for if we see some killed for want of it, there are few less whom the lumber of arms helps to destroy, either by being overburdened, crushed, and cramped with their weight, by a rude shock, or otherwise. For, in plain truth, to observe the weight and thickness of the armour we have now in use, it seems as if we only sought to defend ourselves, and are rather loaded than secured by it.”
Soldier and chronicler Pierre de Brantôme, a contemporary of Montaigne, likewise declared that men who wear heavy armor are “spent at thirty years.”
François de la Noue, a Huguenot captain known as “Iron Arm,” wrote much the same thing in Discours Politiques et Militaires, also published 1587: “Our men of arms in the time of King Henry made a far fairer show … their armor wasn’t very heavy, so that they were well capable of wearing it for 24 hours. Those armors that are worn now are so weighty, that they will deaden a 35-year old Gentleman’s shoulders. I myself have seen the late Lord of Eguillie, and the knight of Puigreffier, honorable old men both, remain fully armed for a whole day, marching in the face of their companies — whereas now a young captain can hardly bear to remain fully armed and armored for two hours.”
If armor was then falling out of fashion in France and elsewhere on the continent, things were much the same in England, and at much the same time. The English poet and adventurer Sir Philip Sidney was shot in the thigh at the Battle of Zutphen in 1584, and died of an infection caused by that wound. As Sir John Smythe describes it, Sidney’s death was because he wasn’t wearing all of his armor; just before the battle, he had noticed that one of his men was not fully armored, so he removed some of his own armor on the grounds that it would be dishonorable to be better armored than his troops.
Sidney’s death set off a heated controversy between English military experts of the era. De la Noue’s Discours was published in London, in English, in late 1587. In 1590, Smythe, a cousin of Edward VI and a lifelong soldier-of-fortune, wrote a small book on military matters titled Certain Discourses, wherein he came to the conclusion that armor is effective against every threat, except for the increasingly popular musket — “the blows of the bullets of which no armours wearable can resist.” He disparaged the musket and the arquebus for many other reasons — noting, for instance, that they are slower to fire than the traditional English longbow, less accurate, and can be difficult to use in poor weather — but was unequivocal about their ability to pierce armor.
Sir Roger Williams and Humphrey Barwick both released books on the same topic later that same year, 1590. Williams, who like Smythe had seen a great deal of battle on the continent, disagreed with Smythe on many points — but not on the musket, “the best small shot that ever was invented.” Barwick, a war-hardened mercenary and adventurer like the others, was analytical about it, noting that “The musketes are weapons of great force, and at this day, bothe with leaders and followers, much feared: for fewe or no Armours, will or can defend the force thereof, being neerehand, which is as well a terror to the best armed, as to the meanest: it will kill the armed of proofe at ten score yardes, the common armours at twenty score, and the unarmed at thirty score, being well used in bullet and tried powder.”
In other words, Barwick claimed that the musket can kill men wearing armor of “proof” — the heavy stuff which, generally, was built to stop firearm rounds — within 200 yards; that it can kill men wearing “common armor” — mass-produced iron armor, called munitions-grade, generally much thinner and of poorer construction than armor of proof — at 400 yards; that it can kill unarmored men at 600 yards. No surprise, then, that the musket was much feared, by armored and unarmored men alike.
Although they disagreed on many important points, all of the aforementioned experts bemoaned the fact that the armor and helmets of their era had become very thick, very heavy, and that its aesthetic qualities and its functionality both suffered for it. Plate armor had reached its zenith — in functionality as well as in artistry — right around the year 1500, but it was evidently falling out of favor by 1580, thanks in large part to the development and increased utilization of the musket.
And indeed, just a few decades after this public debate raged across Europe, the Swedish attained great military victories in the Thirty Years’ War with very lightly armored and highly mobile musketeers and artillery. Although they didn’t invent the musket, they perfected its use — and they can stake a good claim to having invented mobile artillery with the famous leather cannon and the subsequent development of the light 3-pound gun, which could be pulled by two horses and operated by two men. As Gustav’s adversary Montecuccoli noted, and later emulated in battle, “one is appointed to load and fire, and the other conducts it by the end of the carriage, and brings it forward at the march tempo of the infantry.”
With respect to armor: Gustav II Adolf personally stopped wearing armor following a bullet wound to the shoulder sustained at the Battle of Dirschau in 1627. Ever since, he entered battle without armor — even to much larger battles than Dirschau, and to much greater victories. Gustav’s officers were naturally inclined to follow suit — either because they wanted to emulate their leader, or because they felt that it would be shameful to be better-armored than Gustav himself, or merely to lighten their burden.
In the ranks of Gustav’s infantry, pikemen were issued light steel helmets and breastplates, but his musketeers and artillerymen — who outnumbered pikemen by at least two to one — were never issued body armor, and rarely wore helmets.
The cavalry situation was much the same. The heavy cavalry, the Cuirassiers, were issued very light armor, if any at all, which would at most consist of a helmet and pistol-proof breastplate. They frequently wore no more armor than a buffcoat — a heavy leather jacket, as much as 5mm (~0.2”) thick, that offered limited protection against slashing attacks, but none at all against firearms or pike-thrusts. Gustav’s Dragoons — who were, practically speaking, a mounted infantry force — were not issued armor at all, and were armed in the manner of infantry musketeers. “They took us for musketeers, seeing that no animal in the world is more like a musketeer than is a dragoon, and if a dragoon falls from his horse, he rises up a musketeer.”
Gustav II Adolf’s lightly-armored force won key victories with speed and concentrated firepower, and battles like Breitenfeld (1631) marked a turning point in the history of warfare: For the first time, overwhelming firepower, in the form of muskets and light artillery, were utilized as the primary and decisive weapons of war. This presaged the era of maneuver warfare. Also, because it ushered in the demise of expensive steel armor, and because musketeers and gunners were fairly easy to recruit and train, these innovations also enabled, by 1670, a permanent increase in the size of standing armies. For these reasons, among others beyond the scope of this post, Gustav was rightly called “the father of modern warfare” by 19th and 20th century historians.
Thus by the late 16th century, soldiers were discarding their heavy “proof” armor and war-hardened military experts were publicly deriding it. By the mid 17th, the musket and light cannon had attained battlefield supremacy, and breastplates and helmets, once considered essential, were no longer issued to most troops. Musketeers no longer wore helmets; they wore hats, often with very broad brims, as depicted more or less correctly in most of the artwork inspired by Dumas’ Three Musketeers. Of course, this doesn’t mean that armor vanished, for there were more than a few holdouts — particularly in the heavy cuirassiers, who fought primarily with sword and pistol into the 19th century. Ersatz armor was also used for decorative, morale, or aesthetic reasons. Most famously, the spiked German pickelhaube, which was made of leather with metal fittings. More to the point, however, are the iron-tin breastplates and helmets of the later cuirassiers and such units as the Jager-zu-Pferde, but these gleaming accoutrements were very thin, and softer than they looked; like the Pickelhaube, they offered very little protection.
So it was that at the outset of World War One, soldiers were issued no protective armor of any kind. In a perhaps apocryphal story from early in the war, it is said that Intendant-General August-Louis Adrian of the French army was speaking to a wounded soldier, who told him that an inverted mess bowl worn under his cap saved him from a gravely serious head wound. General Adrian is said to have realized that protective headgear might save the lives of French soldiers, and experimented with a metal skull-cap (calotte métallique, cervelière) to be worn under the standard-issue military hat (kepi). This skull-cap was 0.5mm thick, made of mild steel, and offered limited protection against fragments, shrapnel, and blunt impact — yet its use led to a measurable decrease in the number of head-wound casualties. Between December 1914 and February 1915, 700,000 of these skull-caps were made, and 200,000 of them were issued to the ranks.
The skull-cap caught the attention of General Adrien’s superior, Marshal Joseph Joffre, and in April 1915 Joffre ordered General Adrien to set to work on a more sophisticated solution. The Paris Fire Brigade’s helmet was rapidly adapted for wartime use and designated the “Casque Adrian.” It was 0.7mm thick, made of mild steel, and weighed roughly 1.8 pounds. Initially developed only for infantry, it was quickly distributed to all branches of the military. By the end of 1915, over 3 million Adrian helmets had been issued to the ranks.
The British and Germans — among many other nations — quickly followed in the footsteps of the French.
The British issued a helmet designed by John Brodie in 1916. Initially made of mild steel, it was quickly recognized that Hadfield manganese steel — an austenitic steel containing 13% manganese and 1.2% carbon, which was patented in 1883 — would offer significantly better ballistic protection. Hadfield manganese steel exhibits very pronounced strain-hardening effects — it rapidly transforms from ductile austenite to strong and hard martensite when it’s impacted or subjected to compressive or tensile loading. Hadfield steel is also, like all austenitic steels, nonmagnetic, and this was important for soldiers who needed to rely upon compass readings. The Brodie, as-issued, was 0.9mm thick, and weighed roughly 1.3 pounds in total. It was primarily designed to protect from falling shrapnel, so it was built with a broad brim. Overall, it is extremely reminiscent of the medieval kettle hat or chapel de fer.
The Germans, for their part, began work on a helmet for general issue in late 1915. (Earlier in 1915, Lt.Col Hesse, the chief of staff of Army Group Gaede, purchased custom-designed helmets for his unit out-of-pocket. The “Gaede skullcaps” were effective, but were of a peculiar design, and were not adopted by the rest of the German army.) The now-iconic German stahlhelm was developed by Prussian engineering professor Friedrich Schwerd of the Technical Institute of Hanover, and was issued to German troops in early 1916. Metallurgically, these helmets were made of a superior chromium-nickel alloy, were 1mm thick, and were quenched and tempered to a martensitic microstructure and a hardness of 49-54 Rockwell C. The design of these helmets was inspired by — and indeed owes much to — the late-medieval sallet, which the Germans simply called “the Gothic helmet.” (The sallet was extremely popular in Germany in the 15th and 16th centuries.) The old sallet was typically worn with a visor, and a visor was indeed envisioned for the new German steel helmet, but was never put into production. In terms of performance, the German stahlhelm proved to be the best helmet of the war by a substantial margin — for it was thicker than the rest, it utilized the strongest steel alloy, it was offered in numerous sizes, and it offered a superior area of coverage.
But it was the Brodie helmet which formed the basis of subsequent American helmet development. In 1917, the American Expeditionary Forces of WWI were equipped with Brodie helmets; first from a purchase of 400,000 British surplus units, and then from an American-made copy of those helmets, designated the M1917 Kelly. Nearly 3 million American M1917 helmets had been produced before the end of the war.
Steel helmets were adopted by the militaries of almost all European nations during WWI and in the interwar period, and the very vast majority of these were substantially similar to the Adrian, Brodie, or stahlhelm. On the whole, the steel helmet saw little change heading into WWII.
In 1940, the Germans replaced their helmet alloy, which contained as much as 2.5% nickel, with a silicon-manganese alloy, similar to AISI 5140, which contained no nickel at all. This was on account of nickel’s scarcity and high cost in wartime — and it proved a wise move, as the Si-Mn alloy had mechanical properties which were effectively identical to the Ni-rich alloy it replaced; it was also tough, predominantly martensitic, and exhibited hardness of around ~51 HRC on average.
In 1941, prior to America’s entry to the war, the M1917 was replaced by the M-1 helmet, which was larger, bowl-shaped, and eschewed the Brodie’s broad brim in favor of more protection for the sides and back of the head. The M-1 helmet shell was .94mm thick on average and, like the M1917, was made of the same Hadfield manganese steel. It weighed approximately 2.25 pounds without the liner and chinstrap; 3 pounds, 2 ounces in total. Millions of M-1 helmets were produced — over 22 million just between 1941 and 1945 — and they were the standard-issue helmet for US military forces until 1983. For all those many decades, there were effectively no changes made to the composition, thickness, or shape of the M1.
This is not to say that the US Military didn’t experiment with other helmet alloys or materials between the 1940s and 1980s. To the contrary, it did quite a lot of work along those lines — mostly in fiber composites, with Doron helmets, nylon helmets, and many other abortive prototypes. There was some work, also, with polycarbonate as a helmet material. Most of these experiments were interesting, and some of them performed better than the M1’s Hadfield steel, but it was nevertheless determined that “in essentially all candidate materials, the relative gains afforded by a new material or combination thereof were not considered to be cost-effective.”
The more interesting thing is that the US Military never experimented in a serious and methodical manner with better steel helmet alloys. They knew very early on, from experiments with captured helmets, that the German helmets performed considerably better than the M1 on a weight basis, and they also knew that the German Si-Mn alloy — a very lean alloy due to wartime constraints — was by no means the optimal alloy for helmet development. That they made no real efforts to replace Hadfield steel is therefore quite astonishing. In hindsight, a substantial performance improvement, at an equal weight, could have been gained, had they identified and utilized a better alloy.
This must be due in part to the fact that, from the 1940s on, US Military arsenals and research laboratories seem to have been enamored of the idea of a fiber-composite helmet. (Doron was one of the Navy’s favorite pet-projects, and the Army was always deeply enamoured with Nylon.) Thus, when Kevlar was invented, they threw all of their efforts into refining and improving it for use in an entirely new type of military helmet. With Kevlar, and with what they learned from decades of work with Nylon and Doron, the K-Pot was born. But technology could have developed in a different direction — we could have seen thicker helmets of improved steel alloys introduced in the 1980s… that’s just not how things played out.
Diamond Age is now rectifying that: We are reviving the steel helmet. The NeoSteel helmet — which was designed for the European police market, but which exhibits ballistic performance similar to the best fiber-composite helmets in modern military service — is the natural evolution of the steel helmet. It’s what the steel helmet should have already become.
I’ll soon expand on this with a short post on the future of the steel helmet. What we’re doing with novel alloys and advanced forming methods, with accessories, and where it can all go from here… to the theoretical maximum strength of steel, which we have modeled and experimented with. That this also has implications for steel body armor should be clear, and we’re making great strides in that direction, as well.
More to come.
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– The strength and stiffness of a fiber composite does not perfectly correspond to the strength and stiffness of the fibers that it is derived from. The properties of the matrix and the direction of loading must also be taken into account.
