This is another WWII utility knife, designated the M3 Trench Knife or M3 Combat Knife. This knife was the first in a series of military knives and bayonets, utilizing the M3 blade; it is very similar to the US M4 Bayonet used on the M1 Carbine.
The early M3 knives were maker-marked on the blades; later knives were marked on the cross-guard. This knife is an early one and is marked US M3 IMPERIAL on the blade.

Metal finish - all metal parts - were originally blued; later examples were Parkerized. The grip is of the stacked-leather-washer type.

Correct is the M8, fiberglass, green; there was a leather scabbard used early on designated the M6.