The main helmet for American troops in WWII was the M1 steel helmet, adopted in 1941. Ground troops wore it in every theater. Specialist helmets also existed: the M1C for paratroopers, a flak helmet worn by some aircrew, and a photographer’s helmet with a lifting front section. Liners, covers and chin straps came in several patterns as well.
The M1 steel helmet
The M1 had a manganese steel shell and a separate liner that sat inside it, held by a chin strap. Soldiers often wore a helmet cover over the shell, in plain or camouflage patterns, and many surviving covers were replaced over the years. The M1 stayed in use after the war, so a helmet from a later period can look similar to a wartime one. For the wider context of helmets worn in WWII, see World War 2 military helmets.
Paratrooper helmet (M1C)
The M1C was the helmet for airborne troops. Collectors usually identify it by its fittings and chin strap, which differ from the standard M1, rather than by the shell alone.
Aircrew flak helmet (USAAF Mk3)
Some aircrew wore a flak helmet to protect against anti-aircraft fire. It was designed for aircrew, so it is a separate item from the ground-troop M1. Aircrew kit more generally is covered in American WWII pilot uniforms.
Photographer helmet (T-14)
The T-14 was an M1-based photographer’s helmet with a front section that lifted, so that a camera or other equipment could be brought to the face without taking the helmet off.
Liners and covers
The liner is a separate part, and it is often a mismatch in a collection. Check the liner’s fit, its maker and the condition of the sweatband. Helmet covers came in plain and camouflage patterns. A cover that matches the period and the shell is more convincing than one that has been added later.
Checking originality
Start with the maker markings and dates inside the shell’s rim, then check that the liner and chin strap suit the shell. Replicas are common, so compare the details with period photos and reference books before accepting a helmet as original. For the other nations’ helmets, see what helmets did they wear in WWII?