It was common for orders to be issued whereby the helmet was to be worn with the chin strap securely fastened either under the chin or on the point of the chin at all times, either out of neatness (even when not on parade) or to avoid losing the helmet in battle, exposing the soldier to the potential of (perceived needless) injury or death. One reason that was given for soldiers to not wear their helmets with the chin straps fastened was that the concussive blast from a nearby explosion would "catch" on the rim of the helmet and jerk their heads back violently, breaking their necks and killing them; this was recognized as a myth even during the war, but it still persists today for some reason.
There was a twinkle in the eyes of some when they heard of the instructions which had come from First Army concerning helmet chin-straps; they were to be put up over the back of the helmet and never worn fastened under the chin. (In this Regiment it had been one of those unpardonable breeches [sic] of discipline to be seen with chinstraps not properly fastened). Theoretically this order had been originated in order to avoid broken necks resulting from the sudden upward jerk of helmets when the concussion of near bomb or shell hit it. Actually, no such case has ever been authenticated, and it is quite likely that more serious casualties resulted from loss of the helmet at a critical moment than would have from any such effects of the chinstrap.
The 90th Infantry Division Preservation Group analyzed 2,500 photos of American troops from the Normandy campaign, and selected 90 photos that were felt to be representative of the conditions for all troops during that period and where the use of one or multiple M1 helmets could be clearly discerned. 247 helmets were analyzed.
| Chinstrap state | Number | Percentage of total |
|---|---|---|
| Up, and affixed across the back (nape) of the helmet | 119 | 48.18% |
| Chinstraps not visible or not identifiable | 64 | 25.91% |
| Dangling down at the sides of the helmet | 15 | 6.07% |
| Fastened underneath the chin as designed | 15 | 6.07% |
| Up, attached/woven into a helmet net | 14 | 5.67% |
| Placed in the back (nape) of the helmet, between the shell and liner | 5 | 2.02% |
| Entirely missing, torn, or cut off | 3 | 1.21% |
Sources:
Balkoski, Joseph. Beyond the Beachhead: The 29th Infantry Division in Normandy. Mechanicsburg: Stackpole Books, 2005.
Miltonberger, Butler B., and James A. Huston. All Hell Can’t Stop Us! 134th Infantry Regiment Combat History of World War II. n.p.: Army-Navy Publishing Co., 1946.
The M1 Helmet in Normandy: A Case Study, by Chris Guska