For your consideration is this U.S. Military M1 helmet shell liner.
These helmets were used from the second world war through the Vietnam conflict.
The liners were sometimes worn without the steel cover as a stand-alone hard hat of sorts, mostly by rear units and MPs, as well as for ceremonial purposes.
This example is in a green/brown drab and has a patch bearing the acorn insignia of the 87th infantry division.
The condition of the shell is good for the age of this piece, while the suspension is worn and the band is stiff and crispy.
Please see photos for more detail about this great old military collectible!