The ANM2 (Army Navy M2) Caliber .30 Aircraft gun was standardized before the war and used in both Army and Navy aircraft. The 1919A4 was a ground gun which was standardized and used by all branches also. They are two completely different guns with specific applications. Just like an M1 Rifle and an M1 Carbine were standardized and used by all branches but are different guns.
The US only employed a single type of firearm for each purpose as opposed to the Germans who used a multitude of different firearms for the same purpose. The US main rifle was the M1, no other types were adopted. The German main rifles were the 98K, G41, G43, MP43, FG42 and a multitude of captured weapons that certainly did put a strain on the supply chain. So you see, the US did standardize their small arms.
