WWII U.S. M1 Helmet

The M1 helmet was used by the United States from 1941-1985. There were 22,000,000 produced through WWII. The M1 is a combination of two "one-size-fits-all" helmets—an outer metal shell, sometimes called the "steel pot", and a hard liner nestled inside featuring an adjustable suspension system.

Fun Fact: In all, 53 countries have used the M1 style helmet for their military. Of those, 13 are still activity using it.

Sources: Wikipedia