On the Fragment Resistance of the US M-1 Helmet
How does the fragment resistance of the M-1 compare to the PASGT and the ACH? There’s a lot of confusion on this point, with many online sources saying that it has a 17gr. (or equivalent) fragment-simulating projectile (FSP) V50 in the 1300-1350 foot per second range – and some others, including older Adept articles, saying that its 17gr. FSP V50 is 1000 fps or “well below.” Which answer is the right one?
I’ll cut right to the chase:
Before the late 1950s: 17gr. FSP V50 = 900 fps minimum. In practice, tested with cotton liner, usually around 950-1075 fps.
1960s and 70s: Nylon liner introduced. Tested with liner, helmet V50 increased to over 1300 fps on average.
So the 1000-fps-or-below answer was correct for WWII and Korean War M-1 helmets. The 1971 Natick report “Development of a New Acceptance Criterion for M-1 Helmets. Phase 1. Analyses of Data and Development of Inspection Plan” – which evaluated the effect of steel helmet shell thickness on V50 – noted that “the current specification requires a helmet ballistic limit of at least 900 fps when tested in accordance with MIL-K-1988E. An obvious way to assure that current helmet quality will be maintained is to set a minimum acceptable average thickness corresponding to a Vp50 of 900 fps.” (In the same way, the PASGT specification calls for a V50 of 2000 fps.) All sources are in agreement that the M-1’s resin-impregnated duck cotton liner offered no additional ballistic resistance, because anything that penetrates the metal shell will still be moving fast enough to penetrate the cotton liner, and thus the M-1’s performance requirement stood at a 900 fps V50.
In the late 1950s, a nylon M-1 helmet liner was introduced as a replacement for the cotton one. At the same weight (10.1 ounces, ~286 grams,) the nylon liner had a 17gr. FSP V50 of 818 fps, whereas the older cotton liner had a V50 of 345 fps. The nylon liner by itself was thus nearly equal to the whole helmet’s performance requirement! A sample steel helmet tested with the cotton liner had a V50 of 1050 fps; that same helmet with the nylon liner had a V50 of 1330 fps.
To reiterate, there’s the answer: The WWII and Korean M-1s had a 900 fps V50 requirement, and in practice were usually around 950-1075 fps; the Vietnam M-1s were more robust on account of their nylon liners, generally coming in at 1300-1350 fps. Both “under 1000 fps” and “1350 fps” are true. 900 fps is the steel shell baseline, and 1350 is the practical maximum when the helmet is worn with the late-50s nylon liner.
Two questions naturally arise: (1) The M-1 helmet is credited with saving a lot of lives in WWII and Korea – how can this be the case if its V50 is so low? (2) If the nylon liner has such good performance vs. fragments, why didn’t they just improve the liner and get rid of the steel shell? I’ll write about those in a future post. For now, I’ll note that the first question has a partial answer in this article which I wrote for Body Armor News.
