The PPD, short for Pistolet-Pulemyot Degtyaryova, is a submachine gun made in the Soviet Union.
Designed in 1934, the PPD was a near direct copy of the Bergman MP 28. The PPD was designed to chamber the new 7.62x25mm cartridge, based on the 7.63x25mm Mauser cartridge used in the Mauser C96 "Broomhandle" pistol. Officially going into military service in 1934, it was not produced in large quantities at the time. Production issues were never solved until 1937, where in 1934, only 44 were produced, and with 23 in 1935. Production only picked up in 1937 with 1291 made, 1115 in 1938 and 1700 in 1939. Little is it known that the PPD was decommissioned entirely in 1939, with factory orders cancelled; this decision was reversed eventually after Degtyaryov's personal intervention with Stalin, as they were good friends.
The PPD uses simple blowback to fire the gun. It seemed to be inspired by the Suomi KP/-31, a similar submachine gun. One of the problems with the PPD was the cost; the PPD had 95 parts and was not easy to mass-produce, due to milled metal parts being used. The PPSh-41 which came later fixed this problem, where it used stamped sheet metal to reduce the cost.
The PPD has three variants, the PPD-34, the PPD-34/38, and the PPD-40. The PPD-34 was the original designation for the weapon when it went into service, while the PPD-34/38 and PPD-40 had minor changes, mostly to make it easier to mass-produce.