Trench knife M3
The regulation M3 knife and its M6 leather scabbard were introduced in March 1943. It was superseded in May 1944 by the M4 bayonet, intended for the M1 carbine. The M4 was not apparently issued in numbers in the ETO before VE-Day.
(from Government Issue, US Army European Theater of Operations Collector Guide, Henri-Paul Enjames)