Here are some reference Web sites & Books that will help in your collecting of the US M-1 helmet.
if anyone else has any to add please do so thanks.
Home of the M-1 Helmet
Top Pots - U.S. World War II Restored Airborne and Infantry Helmets
M-1 Steel Helmet
.: World War Helmets - Articles :.
.: World War Helmets - Etats-Unis :.
U.S. helmet covers
usmc helmet covers
U.S. M-1 Plastic Liners
U.S. M-1 Steel Helmets
Vietnam - Equipment and Uniform