The steel helmet and the aramid/UHMWPE helmet are products of two entirely different engineering traditions.
There’s a science fiction story by Harry Turtledove called “The Road Not Taken,” which has two core plot devices: (1) That faster-than-light and antigravity technologies are simple and obvious, but that humanity had somehow missed them — and, (2), that as soon as any nascent technological culture discovers those technologies, they obsess over them, and scientific progress in all other directions stagnates. It’s a good story. To excerpt a little bit from its sequel, which summarizes it:
“Back then, on Terra, they knew FTL travel was impossible forever. It was a rude shock when they found that a couple of simple experiments could have given them the key to contragrav and the hyperdrive three, four, even five centuries earlier.” [Note: In the 1500s.]
“How did they miss them?” Chang asked.
“No idea — in hindsight they’re obvious enough. What’s that race that flew bronze [faster-than-light] ships because they couldn’t smelt iron? And every species we know that reached what the old Terrans would have called a seventeenth-century technological level did what was needed — except us.”
“But trying to explain contragrav and the hyperdrive skews an unsophisticated, developing physics out of shape. With attention focused on them, too, work on other things, like electricity and atomics, never gets started. And those have much broader applications — the others are only really good for moving things from here to there in a hurry.”
With a chuckle, Chang said, “We must have seemed like angry gods when we finally got the hyperdrive and burst off Terra. Radar, radio, computers, fission and fusion — no wonder we spent the next two hundred years conquering.”
(From “Herbig-Haro,” sequel to “The Road Not Taken,” by Harry Turtledove.)
In Turtledove’s stories, those technological societies that have somehow missed the development of FTL are said to be traveling down “the road not taken.”
Over the past 80 years, steel armor technology has been the road not taken. Hadfield’s manganese steel, though it turned out to be a real workhorse, is 140 years old. The use of martensitic, high-hardness grades of steel in armor dates back to WWI. The NeoSteel helmet is the only steel armor product that couldn’t have been issued in the 1940s.
And yet, even neglected and ignored, steel is by no means inferior to the best modern materials which see use in helmets. Consider:
– Steel helmets last longer than those made from polyethylene, and are more durable to field conditions.
– Behind-helmet trauma and TBI are less of a concern with steel, for it is incapable of significant plastic deformation.
– Steel helmets offer a superior practical area of coverage, for there are no edge effects with steel. The helmet’s ballistic material won’t roll if it’s hit near the rim.
– As steel helmets don’t deform much upon impact, they can be used with thinner pads — this decreases the profile of the helmet, reducing its silhouette, and thereby presents a smaller target to the enemy. What’s more, a closer fit improves stability.
– Steel handgun armor is qualitatively different from rifle-rated steel body armor. Given the lower velocity, different composition, and typically higher diameter of handgun projectiles, there are far fewer issues with respect to bullet fragmentation.
– The NeoSteel helmet offers ballistic performance that is comparable to, if not superior to, the best polyethylene-based helmets.
The polyethlene helmet has, admittedly, a marginally better ballistic-performance-to-weight ratio — but, in most if not all other respects, including blast and blunt impact performance, the modernized steel helmet is superior. What’s more, there is still considerable room for improvement in steel alloy development and processing for helmet applications, whereas improvements in polyethylene materials are, at this point, likely to be much more modest and incremental.
Truly, steel helmets and fiber-composite helmets are similar only insofar as they’re both helmets. They differ markedly in most other respects, from how they are made, to their material characteristics, to how they respond to impact. The modern steel helmet owes a great deal to Cold War-era steel helmets, and to more recent European and Russian advances in titanium helmets. The composite helmet is the product of an entirely different technological lineage. It owes its existence to the tremendous amounts of effort which the US and UK Militaries had spent on fiber-composite body armor systems, dating back to WWII — first with Doron, then with nylon and various nylon laminates, then with Kevlar, and now with UHMWPE.
Technological products always have traceable lineages.  The steel helmet is the product of one engineering tradition, and the composite helmet is the product of another.
There’s an evolutionary perspective to this. In nature, there are two closely-related notions: Convergent evolution and recurrent evolution. In the former, traits that are adaptive from an evolutionary perspective will arise in organisms that aren’t necessarily related. In the latter, traits that are adaptive will evolve repeatedly over time. The eye — a light-sensing organ — seems to have evolved independently more than 50 times. The wing, likewise. These are evolutionarily favored forms; they are broadly adaptive. It’s extremely plausible that they will arise wherever in the universe there is multicellular life.
Armor itself is an excellent example of a favored and broadly adaptive trait. In fact, it is the ur-adaptive trait. The earliest forms of multicellular life were armored — instead of excreting unwanted trace elements and metabolic byproducts as waste, they secreted them on the outside of their bodies, and let predators break their teeth and blunt their claws on these new hard shells. And our distant ancestors certainly needed strong shells to survive the Cambrian — that they might be ignored by the mighty anomalocaris in favor of flimsier prey.
Since the Cambrian, armor has become a fairly generic feature of life on Earth — but it has had ample time to diverge substantially, and it has taken many different paths. Clearly, the mollusc, the beetle, and the fish have all taken very obviously different approaches.
As in nature, with the profusion of armor types in the natural world, the helmet is as old as human civilization, and there is tremendous divergence in how helmets can be made. Our ancestors armored themselves with metals, with fibers, with animal skins, with stone, with wood, with tree barks and resin, or with “composites” derived from the combination of these materials.
Today’s options are narrower, consisting solely of metals, fiber composites, and plastics. All metal helmets are broadly similar in how they’re made and used, and in how they respond to ballistic impacts. All fiber composite helmets, likewise — whether they’re made of glass fibers, aramid fibers, polyethylene fibers, ceramic fibers, or something else.
Which brings me to a point I had made previously, and which should be re-stated: Since the 1950s, the US military has heavily prioritized research and development in fiber composite helmets, and metal helmets have not received the same attention. The fiber composite helmet is a product with a traceable lineage that dates back 80 years. The steel helmet, neglected for 80 years, has no such lineage, and steel helmet development has become the path less traveled… But we’re walking that path, and we’re confident that steel helmets will soon exceed fiber-composite helmets in every respect. In most respects, they’re already there.
 – The more complex the product, the more complex the lineage tends to be; your cell-phone is the product of numerous advances in transistor and network technologies that were developed at Bell Labs decades ago, but it also owes much to the development of the OLED, to software that was developed by Nokia in the 90s, and to functional ergonomic and form-factor studies carried out by Apple. A deep and complicated lineage, that — and one with many great names involved: John Bardeen, Claude Shannon, Steve Jobs. The German stahlhelm, in contrast, was simply a sallet or salade — made with industrial tools, along industrial lines, and standardized.