Amerian have submachines too. tommy and grease gun.
So so far as automatic weapons are concerned,
Americans were leaders in WWII. German Stg44,
assault rifle, on which AK-47 was based on,
came too late ine the war and did not play a big
role. Most of German infantry use bol action rifle
like Japanese.
Americans did not emphasize on light machinegun.
BAR was used as squad automatic weapon. Maybe
the reason was that M1 was so powerful
so that the role of light machinegun was
not very critical anymore.