In 1925 the USSR began a program to develop a heavy machine gun for antiaircraft use. After some initial experimentation with a converted Dreyse machine gun, they brought in Degtyarev to scale up his recently-adopted light machine gun to the task. Degtyarev’s first design was ready in 1930, and underwent testing until 1933. It was designated the DK, and used a 30-round drum magazine. This contributed to an unacceptably low rate of fire (~360 rpm), and the feed system was replaced by an ingenious development of Georgiy Shpagin to use belts instead.
Fitted with the Shpagin feed system, the DShK finished field testing in 1939 and was adopted as the model 1938. Production was slow, and the guns were not used on anything like the scale of American M2 use during World War Two. A total of about 9000 were in use at the end of the war, although the subsequent update to the DshKM (aka DShK 38/46) pattern would see it fitted to many armored vehicles, and total production eventually topped one million.
This example is a very early production 1939 example, most likely a Finnish capture piece from the Winter War or Continuation War.