My Great Grandfather also brough back helmets from WWII.
This is an M1 Helmet with rectangular swivel bales stamped: 85B and "21" MSA Liner
This is not "his" helmet but It has a name on the inside that reads:
Kenneth O Hudson
Im not sure who he is but I am still looking into it, I am starting to think it could be a fake name. And unfortunetly time has chiped away most of his ID Number.