Helmet covers and netting would be applied by covering the steel shell with the extra material tucked inside the shell and secured by inserting the liner. The liner can be worn by itself providing protection similar to a hard hat, and was often worn in such fashion by military policemen, Assistant Drill Instructors (known as AI's), and rifle/machine gun/pistol range staff, although they were supposed to wear steel at the range.The depth of the helmet is 7 inches, the width is 9.5 inches and length is 11 inches.The design of exterior metal led to some novel uses: When separated from the liner, the shell could be used as an entrenching tool, washbasin, bucket, and as a seat.The shell was also used as a cooking pot but the practice was discouraged, as it would make the metal alloy brittle. The outer part is shaped to fit snugly into the steel shell.The bulk of the helmet is constructed from a single piece of pressed hadfield manganese steel.
It should be noted that no distinction in nomenclature existed between wartime front seams and post war shells in the United States Army supply system, hence World War II shells remained in use until the M1 was retired from service.
Early World War II production helmets had fixed, rectangular loops, and late-war and 1960s helmets feature movable rectangular loops which swiveled inward and outward.
This swivel feature was adopted in 1943 to address the problem that when earlier helmets were dropped, the loops were more susceptible to breaking off.
The liner chinstrap is snapped or riveted directly to the inside of the liner and does not have bails like the shell chinstrap, but it still swivels inside the helmet.
The liner chinstrap is usually seen looped over the brim of the shell and helps to keep the shell in place when its own chinstraps aren't in use.