The U.S. Army entered the war with the M1911 “Montana Peak” hat as its standard headgear, reflecting decades of slouch hat designs influenced by service in the American West. The M1911 was not suitable for trench warfare and was replaced by the helmet on the front line and the side cap or “overseas cap” behind the lines, like this enlisted example. A copy of the French Army issue cap, American versions varied widely in design details.