Shortly after the US declaration of war in April of 1917 the US ordered around 400,000 helmets from the British for use by the American Expeditionary Force. While the US Manufacturers developed their own M1917 helmet and got production up to speed, very few of the M1917s made it to the Western Front before the Armistice. It was replaced by the M1917AI in the late 1930s - 1941 and the M1 helmet and liner was phased in 1941 - 1942.