The Lewis Gun was a light machine gun the USdeveloped and used in World War I. Colonel Isaac Newton Lewis created the gun and logically, America would've adopted it but it didn't happen that way.
Lewis and US General William Crozier didn't get along and eventually Lewis became frustrated trying to convince the US Army to adopt the design, saying it was 'slapped by rejections from ignorant hacks' and he retired from the army. He pitched it to the British, who used the gun for many wars following, as did the US, eventually.
The Lewis Gun Hardware
The Lewis Gun
“The US didn't adopt it due to a disagreement among officers.”