During WWII more than 2000 ZPU (meaning “anti-aircraft machine gun mount”) were in service of Red Army. One of them was triaxial GAZ-AAA truck with mounted quad M4 Maxim machine gun.
The first dedicated Soviet mount for anti-aircraft machine guns was developed around 1928 by Tokarev and was adopted for service in 1931. It was a base for mounting up to four 7.62 mm PM M1910 (Russian Maxim) guns. This was also called a ZPU, although the name М-4 was also assigned to it.
M-4 Maxim machine gun has the device of compulsory water circulation and bigger capacity of machine-gun tapes — 1000 cartridges, instead of usual 250.
Using antiaircraft ring sights, M-4 was effective in fire on low-flying planes (at the height up to 1400 m at a speed up to 500 km/h). M-4 was also often used for infantry support.
M-4 served the Soviet armed forces in all major conflicts until 1945.
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