Nkm wz.38 FK
Encyclopedia
The Nkm wz.38 FK was a 20mm heavy machine gun
(autocannon
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
tankette
s. Mass-produced in 1938 and 1939, it was used extensively during the September Campaign.
s 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..
The prototype, dubbed nkm
model A, was built already in November of 1937. It was tested and by March of 1938 most design flaws were eliminated. During additional tests it showed excellent penetration capabilities: it could penetrate 40mm of steel armour at 200 metres distance. It was found better than the competing foreign products as an anti-tank weapon and anti-air gun. However, usage as aircraft weapon was discouraged due to low firing rate and the new weapon was found slightly too heavy for infantry and cavalry use. Because the test results were satisfactory, in May of that year the Polish Army ordered additional two copies for additional tests.
As an anti-tank weapon for infantry use the gun was to be mounted on two types of mountings: light (a simple tripod
) and heavy (modified mounting used by 37mm Bofors AT gun
). With time the Polskie Zakłady Optyczne works also designed new anti-air sights (similar to those used in 40mm Bofors AA gun) and the gun was finally accepted for service under the official designation nkm wz.38 FK, the FK being the acronym of the lead design bureau at Fabryka Karabinów.
A first batch of 100 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 of 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.
However, the initial costs were high. The design itself, factory equipment and the guns of the first batch themselves cost roughly 2.2 million złoty. 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.
it was to be mounted on PZInż. 130 amphibious tanks, as well as 4TP light tank
s. In addition, as a stop-gap solution roughly 100 TK-3 and TKS
tankette
s were to be 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. Also all anti-tank companies were to be eventually reequipped with this gun.
However, as by September 1, 1939 the overall production did not exceed 55 pieces, only 40 were mounted on TK-3 and TKS tankettes. The fate of the 15 pieces on infantry mountings remains unknown.
role. In January of 1939 the new TKS tankette armed with 20mm HMG was accepted into service. A major drawback of this stop-gap solution was low load of a tankette - it could transport only a limited supply of ammo. However, it also offered high mobility and very low profile.
was fixed with a muzzle brake
with a flame suppressor. The weapon was fed either with small box magazines for 5 or 10 bullets, or drum magazine
s for 15 or 100 bullets.
The specially-designed 20mm ammunition was based on 20x138mm Solothurn long
shell. It was produced in several configurations: armour-piercing tracer, incendiary tracer, as well as training round and training tracer round. The set was later extended to include also AA ammunition, HE tracer.
nota bene: Capable of destroying any German tank of 1939 except for possibly Panzer 4 (Panzer 4 was used in Poland in field test
numbers; yet, some got destroyed) and Czechoslovak--made Panzer 38(t)
.
Heavy machine gun
The heavy machine gun or HMG is a larger class of machine gun generally recognized to refer to two separate stages of machine gun development. The term was originally used to refer to the early generation of machine guns which came into widespread use in World War I...
(autocannon
Autocannon
An autocannon or automatic cannon is a rapid-fire projectile weapon firing a shell as opposed to the bullet fired by a machine gun. Autocannons often have a larger caliber than a machine gun . Usually, autocannons are smaller than a field gun or other artillery, and are mechanically loaded for a...
by modern terminology) produced in inter-war Poland
Second Polish Republic
The Second Polish Republic, Second Commonwealth of Poland or interwar Poland refers to Poland between the two world wars; a period in Polish history in which Poland was restored as an independent state. Officially known as the Republic of Poland or the Commonwealth of Poland , the Polish state was...
. It was used both in anti-air and anti-tank role, it was also adapted to tank use
Tank gun
A tank gun is the main armament of a tank. Modern tank guns are large-caliber high-velocity guns, capable of firing kinetic energy penetrators, high explosive anti-tank rounds, and in some cases guided missiles. Anti-aircraft guns can also be mounted to tanks.-Overview:Tank guns are a specific...
and mounted on some TKS
TKS
The TK and TKS were Polish tankettes during the Second World War.-Design and development:The TK tankette was a Polish design produced from 1931 that was based upon an improved chassis of the British Carden Loyd tankette. The TKS was an improved model with a new hull and a more powerful engine...
tankette
Tankette
A tankette is a tracked combat vehicle resembling a small tank roughly the size of a car, mainly intended for light infantry support or reconnaissance. Colloquially it may also simply mean a "small tank"....
s. Mass-produced in 1938 and 1939, it was used extensively during the September Campaign.
Origins
In early 1930s the Polish Army was looking for a modern anti-tank and anti-air weapon to replace outdated WWI equipment still in use. In 1931 heavy machine gunHeavy machine gun
The heavy machine gun or HMG is a larger class of machine gun generally recognized to refer to two separate stages of machine gun development. The term was originally used to refer to the early generation of machine guns which came into widespread use in World War I...
s made by Hotchkiss
Hotchkiss et Cie
Société Anonyme des Anciens Etablissements Hotchkiss et Cie was a French arms and car company established by United States engineer Benjamin B. Hotchkiss, who was born in Watertown, Connecticut. He moved to France and set up a factory, first at Viviez near Rodez in 1867, then at Saint-Denis near...
, Solothurn
Solothurn
The city of Solothurn is the capital of the Canton of Solothurn in Switzerland. The city also comprises the only municipality of the district of the same name.-Pre-roman settlement:...
and Oerlikon
Oerlikon Contraves
Rheinmetall Air Defence AG is a division of German armament manufacturer Rheinmetall, created when the company's Oerlikon Contraves unit was renamed on 1 January 2009 and integrated with Rheinmetall's other air-defence products...
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
Madsen
-People:*Barbara Madsen, American Judge, Washington Supreme Court Justice*Birger Madsen, Norwegian professional football defender*Bo Madsen, guitarist of the Danish rock band Mew*Chris Madsen, Danish-American lawman of the Old West...
and Hispano-Suiza
Hispano-Suiza
Hispano-Suiza was a Spanish automotive and engineering firm, best known for its luxury cars and aviation engines in the pre-World War II period of the twentieth century. In 1923, its French subsidiary became a semi-autonomous partnership with the parent company and is now part of the French SAFRAN...
. 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..
The prototype, dubbed nkm
HMG
HMG may refer to:* Heavy machine gun* Her Majesty's Government is the formal title for the British Government. If a the monarch is a king, the title changes to "His Majesty's Government"...
model A, was built already in November of 1937. It was tested and by March of 1938 most design flaws were eliminated. During additional tests it showed excellent penetration capabilities: it could penetrate 40mm of steel armour at 200 metres distance. It was found better than the competing foreign products as an anti-tank weapon and anti-air gun. However, usage as aircraft weapon was discouraged due to low firing rate and the new weapon was found slightly too heavy for infantry and cavalry use. Because the test results were satisfactory, in May of that year the Polish Army ordered additional two copies for additional tests.
As an anti-tank weapon for infantry use the gun was to be mounted on two types of mountings: light (a simple tripod
Tripod
A tripod is a portable three-legged frame, used as a platform for supporting the weight and maintaining the stability of some other object. The word comes from the Greek tripous, meaning "three feet". A tripod provides stability against downward forces, horizontal forces and moments about the...
) and heavy (modified mounting used by 37mm Bofors AT gun
Bofors 37 mm
The Bofors 37 mm gun was an anti-tank gun designed by Swedish manufacturer Bofors in the early 1930s. Licensed copies were produced in a number of countries. The gun was used by some European armies during World War II, mainly at the early stage of the war.-Development history:The gun was...
). With time the Polskie Zakłady Optyczne works also designed new anti-air sights (similar to those used in 40mm Bofors AA gun) and the gun was finally accepted for service under the official designation nkm wz.38 FK, the FK being the acronym of the lead design bureau at Fabryka Karabinów.
A first batch of 100 HMGs was ordered on August 26, 1938. The gun was produced by Sanok
Sanok
Sanok is a town in south-eastern Poland with 39,110 inhabitants, as of 2 June 2009. It's the capital of Sanok County in the Subcarpathian Voivodeship. Previously, it was in the Krosno Voivodeship and in the Ruthenian Voivodeship , which was part of the Lesser Poland province...
-based Zieleniewski company, with barrels made by Pruszków
Pruszków
Pruszków is a town in central Poland, situated in the Masovian Voivodeship since 1999. It was previously in Warszawa Voivodeship . Pruszków is the capital of Pruszków County, located along the western edge of the Warsaw urban area...
-based Zakłady Przemysłowe Stowarzyszenia Mechaników Polskich z Ameryki works and newly-designed ammunition at the State Munition Works in Skarżysko-Kamienna
Skarzysko-Kamienna
Skarżysko-Kamienna is a town in northern Świętokrzyskie Voivodeship in Poland by Kamienna river, to the north of Świętokrzyskie Mountains; one of the voivodship's major towns...
. In April of 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.
However, the initial costs were high. The design itself, factory equipment and the guns of the first batch themselves cost roughly 2.2 million złoty. 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
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
out of 896 pieces ordered for delivery by 1940 only 55 pieces were delivered to the Polish Army.
Usage
The Nkm wz.38 FK was to become a standard anti-tank and anti-air equipment of the Polish Army. As a tank gunTank gun
A tank gun is the main armament of a tank. Modern tank guns are large-caliber high-velocity guns, capable of firing kinetic energy penetrators, high explosive anti-tank rounds, and in some cases guided missiles. Anti-aircraft guns can also be mounted to tanks.-Overview:Tank guns are a specific...
it was to be mounted on PZInż. 130 amphibious tanks, as well as 4TP light tank
Light tank
A light tank is a tank variant initially designed for rapid movement, and now primarily employed in low-intensity conflict. Early light tanks were generally armed and armored similar to an armored car, but used tracks in order to provide better cross-country mobility.The light tank was a major...
s. In addition, as a stop-gap solution roughly 100 TK-3 and TKS
TKS
The TK and TKS were Polish tankettes during the Second World War.-Design and development:The TK tankette was a Polish design produced from 1931 that was based upon an improved chassis of the British Carden Loyd tankette. The TKS was an improved model with a new hull and a more powerful engine...
tankette
Tankette
A tankette is a tracked combat vehicle resembling a small tank roughly the size of a car, mainly intended for light infantry support or reconnaissance. Colloquially it may also simply mean a "small tank"....
s were to be 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. Also all anti-tank companies were to be eventually reequipped with this gun.
However, as by September 1, 1939 the overall production did not exceed 55 pieces, only 40 were mounted on TK-3 and TKS tankettes. The fate of the 15 pieces on infantry mountings remains unknown.
Operational history
The armoured units to be equipped with the new 20mm weapon needed a new gun mounting. In mid-1938 TK-3 and TKS tankettes rearmed with the new gun were tested extensively. The new vehicle was to be used primarily in a tank destroyerTank destroyer
A tank destroyer is a type of armored fighting vehicle armed with a gun or missile launcher, and is designed specifically to engage enemy armored vehicles...
role. In January of 1939 the new TKS tankette armed with 20mm HMG was accepted into service. A major drawback of this stop-gap solution was low load of a tankette - it could transport only a limited supply of ammo. However, it also offered high mobility and very low profile.
Description
The Nkm wz.38 FK feature blowback operation. The barrelBarrel
A barrel or cask is a hollow cylindrical container, traditionally made of vertical wooden staves and bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. A small barrel is called a keg.For example, a...
was fixed with a muzzle brake
Muzzle brake
Muzzle brakes and recoil compensators are devices that are fitted to the muzzle of a firearm or cannon to redirect propellant gases with the effect of countering both recoil of the gun and unwanted rising of the barrel during rapid fire...
with a flame suppressor. The weapon was fed either with small box magazines for 5 or 10 bullets, or drum magazine
Drum magazine
A drum magazine is a type of firearms magazine that is cylindrical in shape, similar to a drum. Instead of rounds being stored flat, as in a more common box magazine, rounds in a drum magazine are stored in a spiral around the center of the magazine, facing the direction of the barrel.There are...
s for 15 or 100 bullets.
The specially-designed 20mm ammunition was based on 20x138mm Solothurn long
20x138mmB
The 20×138mmB cartridge was a type of ammunition used mainly for anti-aircraft and anti-tank weapons during World War II. The designation means the caliber was 20 mm, the length of the cartridge case was 138 mm and B indicates it was a belted case...
shell. It was produced in several configurations: armour-piercing tracer, incendiary tracer, as well as training round and training tracer round. The set was later extended to include also AA ammunition, HE tracer.
Penetration Capacity
- Penetration Capacity:
Distance (m) Thickness (mm) Hardened Steel 100 20 200 18 300 17 400 15 500 13 Steel 300 25 400 23 500 20
nota bene: Capable of destroying any German tank of 1939 except for possibly Panzer 4 (Panzer 4 was used in Poland in field test
Field test
A field test may refer to*Visual field test*Field test mode*Field Test, a short film, part of Batman: Gotham Knight...
numbers; yet, some got destroyed) and Czechoslovak--made Panzer 38(t)
Panzer 38(t)
The Panzerkampfwagen 38 was originally a Czech tank of pre-World War II design. After Czechoslovakia was taken over by Germany, it was adopted by the German Army, seeing service in the invasions of Poland and Russia. Production ended in 1942, when its armament was deemed inadequate. In all, over...
.