 The Model 1928 was the first type widely used by military forces, with the U.S. Navy and U.S. Marine Corps as major buyers through the 1930s.The original Model 1928s were Model 1921s with weight added to the actuator, which slowed down the cyclic rate of fire, a United States Navy requirement.On these guns, the model number "1921" on the receiver was updated by stamping an "8" over the last "1".