This is a a fine example of a US Army M1 helmet.
Note that
"Bushmaster" and rank matching decals have been applied to the
helmet and liner.
The shell has a front seam and fixed bails. this is an early version of
the helmet used during WWII.
The liner suspension system seems to be
made up of a combination of WWII and Korean war parts. There are several
marks in the liner but no dates.
The liner has been converted to be used by
paratroopers by adding snaps on the inside.