Nkm wz.38 FK

In early 1930s the Polish Army was looking for a modern anti-tank and anti-air weapon to replace outdated World War I equipment still in use.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 Bolesław Jurek of Warsaw-based Fabryka Karabinów company became the lead designer.[2]

Four designs were considered for the wz 38FK, dubbed Models A-D, from which only the Model A would become adopted;

Model A - heavy machine gun designed by Bolesław Jurek. Adopted by the Polish Army in 1939. Automatic self-repeating weapon. Operating on the principle of short barrel recoil. It had an easily replaceable barrel with a muzzle brake. It is fed from a box magazine with a capacity of 5 or 10 rounds or a drum magazine with a capacity of 15 rounds. It is mounted in the tank with a spherical yoke with an armored cover developed by Napiórkowski and Miniewski.

Model B - prototype of a heavy machine gun developed by W. Lewandowski. A gas operated design which utilised a gas port in the barrel. Fed from a cloth or metal link belt or from a box magazine.

Model C - prototype of a heavy machine gun developed by S. Rytwiński and W. Lewandowski. Operation as the Model B HMG. Fed via 200 round cloth or metallic belt, box magazine for 5-10 rounds or drum magazine with capacity of 100 rounds. A PL20A tripod base was designed for the use of the gun as an anti-tank infantry weapon. The tripod was made according to J. Skrzypiński's design and developed by L.Kowalewicz. In this version, the HMG was to be equipped with a lighter barrel and 5 round box magazine. A heavier PC20A wheeled mount would be used for the weapon when equipped at higher tactical levels.The mount had a weight of 400-500 kg and was developed by L. Kowalewicz. It was predicted that the HMG could be used for arming aircraft.

Model D - prototype heavy machine gun developed by Bolesław Jurek. Works like Model B. Powered by a 100-round drum magazine. Could be used for arming aircraft.[2]

A first batch of 100 Model A HMGs was ordered on August 26, 1938. The gun was produced by Sanok-based Zieleniewski company, with barrels made by Pruszków-based Zakłady Przemysłowe Stowarzyszenia Mechaników Polskich z Ameryki works and newly designed ammunition at the State Munition Works in Skarżysko-Kamienna. In April 1939 another 140 pieces were ordered, 40 of those as stationary weapons (without mountings) and with time the production was to reach 100 pieces a month.[2]

However, the initial costs were high. The design itself, factory equipment and the guns of the first batch themselves cost roughly 2.2 million zlotys. The plans for budget year 1939/1940 amounted to almost 3.4 million. In addition, the initial batch was being manufactured at a much slower rate than expected. Because of that by the outbreak of World War II out of 896 pieces ordered for delivery by 1940 only 55 pieces were delivered to the Polish Army.[2]

The Nkm wz.38 FK was accepted by the Polish Army in 1939. As a stop-gap solution roughly 30 TK-3 and TKS tankettes were rearmed with this HMG. As an anti-tank and anti-air weapon, the gun was to be used extensively: 8 pieces in AA configuration for every infantry division.

However, as of September 1st, 1939 the overall production did not exceed 60 pieces.