38FK

Nkm wz.38 FK
The gun in light infantry configuration
Type	anti-air and anti-tank heavy machine gun/
Place of origin	Poland
Service history
In service	1938-1939
Used by	Poland
Wars	World War II
Production history
Designer	Wawrzyniec Lewandowski
Designed	1938
Manufacturer	Fabryka Karabinów
Unit cost	30,000 zł (tank version)
Produced	1938-1939
No. built	55
Specifications
Weight	57.6 kilograms (127 lb)
Length	2,015 millimetres (79.3 in)
Barrel length	1,476 millimetres (58.1 in)
Width	202.5 millimetres (7.97 in)
Crew	3 (PL 20A mount)/ 6 (PL 20B mount)
Shell	20x138 mmB
Shell weight	320g
Caliber	20 mm
Action	blowback
Rate of fire	320-350 rpm
Muzzle velocity	856 metres per second (2,810 ft/s)
Effective firing range	5,000 metres (5,500 yd)/7,000 metres (7,700 yd)
Feed system	box/drum

The Nkm wz.38 FK (Polish military acronym meaning Heaviest Machine Gun Mark 1938) was a 20mm heavy machine gun ( by modern terminology) produced in inter-war Poland. It was used both in anti-air and anti-tank role, it was also adapted to tank use and mounted on some TKS tankettes. Mass-produced in 1938 and 1939, it was used extensively during the September Campaign.

In line with other arms design of the epoch, the Nkm wz.38 FK was a code-name rather than a proper name of the weapon. The Nkm acronym stands for Polish: najcięższy karabin maszynowy, literally the heaviest machine gun (i.e. heavier than standard contemporary heavy machine guns using standard rifle cartridges such as the 7.92 Mauser, .303 British or 7.62×54mmR). The second part of the name, wz. 38 stands for Polish: wzór 38, that is Mark 1938, referring to the year the weapon was submitted to the military for testing or the year the weapon was designed. Finally, when more than one weapon of certain type was conceived in the same year, additional designation was added at the end to differentiate between various types. In this case the FK stood for Fabryka Karabinów, the Warsaw-based state-owned rifle factory.

In early 1930s the Polish Army was looking for a modern anti-tank and anti-air weapon to replace outdated World War I equipment still in use. In 1931 heavy machine guns made by Hotchkiss, Solothurn and Oerlikon were tested, but were found unsuitable for Polish needs. Most importantly, they could not suit both AT and AA roles well. In 1937 another commission was sent abroad to test the newly designed weapons of 20mm calibre by Oerlikon, Madsen and Hispano-Suiza. As all designs had several flaws, it was decided to start works on an indigenous design. Engineer Wawrzyniec Lewandowski of Warsaw-based Fabryka Karabinów company became the lead designer.