Subgun?

[xm15e2s]

Does anyone know the origin of the term "sub" in the word subgun? Sure Sub in subsonic means below as in below or lower than the speed of sound. So does it mean a machinegun designed to shoot ammo that is subsonic? OR does the sub refer to the cyclic rate or perhaps the small size of the gun? which is it?

 

[tommygun2000]

Does anyone know the origin of the term "sub" in the word subgun? Sure Sub in subsonic means below as in below or lower than the speed of sound. So does it mean a machinegun designed to shoot ammo that is subsonic? OR does the sub refer to the cyclic rate or perhaps the small size of the gun? which is it?

It refers to the fact that it fires a pistol caliber of ammunition as opposed to a rifle cartridge. Meaning sub or smaller machinegun.
Shoulder fired.

A "machinegun" in the original true definition fired a rifle cartridge and was usually a crew served weapon.