M1C helmet

Developed in World War II to replace the earlier M2 helmet, it was not made available until issued to paratroopers in January 1945.

The M2 had fixed, spot welded "D" bales so named for their shape, similar to early M1s.

It used a simple but strong and reliable belt loop-type connection to secure the chinstrap to the a-yokes, which could be opened or closed from either side and thus partially removed without tools.

This retention system was not significantly different to the M2's, and the normal infantry chinstrap could still be attached to the helmet shell if desired.

There's an argument to be made that the important part of an M1C is actually just a liner with the four-point chinstrap that can slip into any M1 helmet.