The Rise and Fall of the 20th Century Steel Helmet
The Decline, Resurgence, and Future of Steel Armor II
In a perhaps apocryphal story from the early days of WWI, it was 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 what might have been a far more serious head wound. General Adrian was 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). The final issued design was a 0.5mm-thick skull-cap made of mild Bessemer steel which offered limited protection against fragments, shrapnel, and blunt impact – yet its use led to a measurable decrease in the number of head-wound fatalities. 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 Bessemer steel like the first prototype skullcap, 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; though normally soft and ductile, it rapidly becomes very strong and hard when it’s impacted or subjected to plastic strain. 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 sallet, which the Germans simply called “the Gothic helmet.” (The sallet having been particularly 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 it 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 best steel alloy, it was offered in numerous sizes, and it offered a superior area of coverage.
Just after entering the war, in June 1917, the US Military launched a “helmet committee” to analyze the performance of European helmets and select a helmet for American troops. They quickly contracted with the Metropolitan Museum of Art’s armor curator, Bashford Dean, to develop a steel helmet for American forces. His design, which was also inspired by the sallet, was deemed “too similar” to the enemy German design, and not distinctive enough, so it was not issued.
From “Helmets and Body Armor in Modern Warfare” by Bashford Dean, 1922.
As Dean was working, the US Army was buying surplus British helmets for emergency wartime use, beginning with a purchase of 400,000 surplus Brodie helmets. Ultimately, they decided to stick with that design, and an American-made copy of the Brodie, designated the M1917 Kelly, was put into production and issued to all troops. Nearly 3 million American M1917 helmets were produced before the end of the war.
Steel helmets 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 with the M1 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 M1 helmet shell was .94mm thick on average and, like the M1917, was made of that same Hadfield manganese steel. It weighed approximately 2.25 pounds without the liner and chinstrap – and just 3 pounds, 2 ounces in total, with the liner. Millions of M1 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 in ballistic tests 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. The East German M1956 helmet was also known to offer exceedingly good protection against handgun rounds and shrapnel. That they made no real efforts to replace Hadfield steel is therefore very surprising. In hindsight, a nearly 50% performance improvement, at an equal weight, could have been gained had they identified and utilized a better alloy.
From the 1940s, 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 looking for more ways to use 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. Technology could have developed in a different direction — we could have seen thicker helmets of improved steel alloys introduced in the 1980s — but that’s not how things played out.
Instead, following research into Kevlar composite helmets in the 1970s, the PASGT helmet and armor system was issued to troops in the 1980s, and first saw use in combat in 1983 during Operation Urgent Fury in Grenada. The PASGT was made of Kevlar-29 and weighed 3.1 pounds for a Size S to 4.2 pounds for a Size XL.
Compared to the M1, it offered considerably improved protection against fragmentation threats, though at a steep cost: Substantially increased weight, and a price tag larger by several orders of magnitude. As a steel helmet of comparable weight and performance, at a much lower cost, could have easily been made with the technologies of the time, it’s hard to view the introduction of the PASGT as anything but a mistake.
Indeed, the rationale behind the adoption of the PASGT helmet is really materials-agnostic: The main problems with the M1 were poor fit and poor perceived comfort.
In a 1956 project titled “U. S. Army protective headgear analysis of design” the industrial design firm of Egmont Arens evaluated combat helmet systems. They ultimately came to the conclusion that there are just three key variables in helmet design:
(1) weight and material
(2) size
(3) suspension
The PASGT was a revolutionary design on all three fronts. It was made of an entirely different material. (And, just to reemphasize, one which was substantially heavier on an areal density basis, with the XL PASGT at 4.2 pounds having a smaller surface area than the M1, at 3.3 pounds.) It was sized very differently, with significant differences to the area of coverage the helmet offered its wearers. It had a far lower center of gravity than the M1. And instead of a rigid fiberglass liner, it offered an adjustable webbing-type suspension system.
It could well be said that the suspension and geometry/sizing changes were clear improvements – but it’s hard to argue that it would have been impossible to make a better helmet, back then, out of steel. A properly-made steel PASGT would have been a better helmet: Roughly equivalent protection from shrapnel at an equal weight; better protection against handgun threats at an equal weight; lower profile with a lower center of gravity, and thus a better fit and improved perceived comfort; cheaper; more durable. We know that all of this is true because the performance of the NovaSteel helmet exceeds the performance of the PASGT’s successor, the ACH.
But the aramid PASGT stuck, and by 1990 had completely replaced the steel helmet in the USA. By 2000, the steel helmet was on its way out, worldwide. And it looked once again as though steel body armor would ride off into the sunset.
