A 1942 study determined that relatively low velocity projectiles such as deflected flak fragments or shattered pieces of aircraft structure caused 70% of bomber crew wounds.  At the time, aircrews only wore fabric flight helmets and with the increasing number of head wounds, it became obvious that more protection was needed.

Early bomber crews wore standard M1 infantry steel helmets directly over their flight helmets but found them uncomfortable since their earphones fit poorly under the steel helmet.  Although relatively effective as protection against metal fragments, bumps, or flying debris, this was not an adequate solution to the problem. Furthermore, it was too bulky for crew positions in gun turrets.

In January 1943, combat crews in the 306^th Bomb Group based at Thurleigh modified the M1 helmets by hammering out the sides and cutting the liner to enable them to be worn over their flying helmets and earphones. The modification gained acceptance by other bomb groups and was formerly adopted as standard issue in early 1944 and designated the M3.

The US Ordnance Department produced the M-3 Anti Flak Helmet by omitting the fiberboard liner and riveting the suspension band directly to the steel outer shell. Designed to fit properly over a flying helmet and its communication equipment the sides were cut out and felt-lined, hinged ear flaps were fitted, plus a long leather chin strap with a quick release buckle. To prevent freeze-burns, a risk when touching bare metal at temperatures well below zero encountered at high altitudes, the helmet was painted with a flocked olive-green finish (sawdust or similar material mixed with the paint).