The M38 Tanker's Helmet

The M38 "Helmet, Tank" was developed in 1938 meeting the following criteria: 1) fits inside an M-1 helmet when shrapnel protection is needed; 2) equipped with microphone and earphones, with connecting jacks; 3) protected the crewman's head from hits on the steel interior.  It first saw service in early 1942.

A Sherman Tank crew wearing M38 helmets at Ft. Knox, 1942