MK 108 cannon

The MK 108 (German: Maschinenkanone—"machine cannon") was a 30 mm caliber autocannon manufactured in Germany during World War II by RheinmetallBorsig for use in aircraft.

MK 108
MK 108 at RAF Museum Cosford
Two MK 108 autocannon, RAF Museum Cosford (2010)
Place of originNazi Germany
Service history
In service1943–1945
Used byNazi Germany
WarsWorld War II
Production history
Mass58 kilograms (128 lb)
Length1,057 millimetres (41.6 in)
Barrel length580 millimetres (23 in)

Cartridge30×90RB mm steel casing
Caliber30 mm
ActionAPI Blowback
Rate of fire650 rounds/min
Muzzle velocity540 m/s (1,770 ft/s)


The weapon was developed as a private venture by the company in 1940 and was submitted to the Reichsluftfahrtministerium (RLM—Reich Aviation Ministry) in response to a 1942 requirement for a heavy aircraft weapon for use against the Allied heavy bombers appearing over German-controlled regions by then. Testing verified that the autocannon was well-suited to this role, requiring on average just four hits with its 85g RDX-load (in a 330g shell) and a resulting strongly brisant high-explosive ammunition, to bring down a heavy bomber such as a B-17 Flying Fortress or B-24 Liberator, and just a single "shattering" hit to down a fighter. In comparison, the otherwise excellent 20 mm MG 151/20 (3g of HE in 57g shell) required an average of 25 hits to down a B-17.

The MK 108 was quickly ordered into production and was installed in a variety of Luftwaffe fighter aircraft. It saw first operational service in late autumn 1943 with the Bf 110G-2 bomber destroyers and in the Bf 109G-6/U4.

Design details


30mm ammo
30x90RB ammunition, as used in the MK 108 Machine Cannon
MK 108 30mm
Side view, MK 108

The cannon used specially-developed 30×90RB mm ammunition—30 mm calibre, 90 mm case length, rebated/reduced rim. Unlike most other weapon rounds, which used traditional brass for the case, the MK 108's ammunition used steel cases. Several types of ammunition were developed, including practice, armor-piercing, high-explosive and incendiary. In operation, however, two major ammunition types were used: Minengeschoß ("mine-shell") and high-explosive incendiary. The Minengeschoß was made by drawn steel (the same way brass cartridge-cases are made) instead of being forged and machined as was the usual practice for cannon shells. This resulted in a shell with a thin but strong wall, which hence had a much larger cavity in which to pack a much larger explosive or incendiary charge than was otherwise possible.


The cannon proved to be relatively light, effective, reliable, compact and easy to manufacture due to its simple construction—80% of the weapon was made from stamped parts, and the number of moving parts was kept to a minimum by using advanced primer ignition blowback (APIB) operation. The MK 108 was optimized for a high rate of fire at the expense of ballistic performance.

It was easy to maintain, and its compact size, low weight and electrical priming made it ideal for aircraft installation. The cannon's distinctive heavy pounding sound and high rate of fire gave it the nickname "pneumatic hammer" amongst Allied aircrews, who feared its destructive power.


Normally, gas-operated or recoil-operated mechanisms are used in automatic weapons of rifle calibre and larger because the chamber pressure in such weapons is very high. Therefore, if a simple blowback system (where there is no positive lock between the bolt and barrel) is used, the bolt may recoil and open the breech while the chamber pressure is still high, causing damage to the weapon and split cases (see blowback article for more information). To avoid this, simple blowback guns have to use low-powered cartridges or a very heavy bolt.

In an Advanced Primer Ignition Blowback design such as the MK 108, the forward motion of the bolt is used instead of a locking mechanism to prevent this premature opening. When the 108 is ready to fire, the bolt and main spring are held back at the rear of the gun, the spring under considerable tension. When the trigger is squeezed, they are released and shoot forward at a high speed. The bolt picks up a cartridge and chambers it, but instead of coming to rest against the breech face, it follows the case a small distance into the chamber—which is of course made specially longer in these guns to accommodate this manoeuvre. Also a cartridge case with a rebated rim is used, so that the extractor claw can hook over the rim and still fit within the chamber.

Primer ignition is timed so that the bolt is still moving forward when the propellant is ignited. The expanding gases from the fired round stop the forward motion of the bolt, then reverse its motion. The key characteristic of the APIB system is that, because the resistance due to the weight of the bolt and the mainspring are supplemented by the bolt's considerable forward momentum, the propellant gases are contained in the barrel for critical microseconds, and the projectile will have had time to leave the muzzle, allowing the gas to escape forward and reducing the chamber pressure to a safe level before the bolt and cartridge case emerge from the opposite end. Once they emerge the weapon cycles like other automatic guns,with one significant exception: instead of simply ejecting the spent cartridge case, the 108 reinserts it into the empty link in the ammunition belt. The heavy bolt continues backwards, compressing the main spring. When the spring is fully compressed it begins to expand forwards again, reversing the motion of the bolt and recommencing the cycle. This sequence is repeated until the trigger is released or the ammunition is exhausted.

The APIB design makes practical the use of far more powerful ammunition than with simple blowback operation, but the length and the speed of the bolt's movement within the chamber are limited by the stresses placed on the case by the sliding motion, which takes place under high gas pressure. To keep these within limits either the bolt must be heavy to absorb the pressure, or the barrel must be short to limit the duration of high pressure within the barrel. The operational tradeoff is that a heavy bolt reduces the rate of fire while a short barrel reduces ballistic performance. The designers of the MK 108 opted for a high rate of fire and thus used a relatively light bolt, accepting reduced ballistic performance due to the corresponding necessity of a short barrel. As a result, the MK 108 had a muzzle velocity of only 540 m/s, compared to 850 m/s for the MG 151/20.

Another significant feature is that, in the APIB system the cycle starts with the bolt open, which prevents an autocannon using the APIB principle from being accurately synchronized with an aircraft's propeller.

MK108 bolt cycle AB
MK108 bolt cycle CD
MK108 feed cycle AB
MK108 feed cycle CD

Operational usage

Left pair in a Me 262

The MK 108 saw widespread use among fighters tasked with shooting down enemy bombers. Some of the aircraft deploying, or intended to be armed with, the MK 108 were Messerschmitt Bf 109, Messerschmitt Bf 110, Messerschmitt Me 163, Messerschmitt Me 262, Focke-Wulf Fw 190, Focke-Wulf Ta 152, Focke-Wulf Ta 154, Heinkel He 162, Heinkel He 219, Horten Ho 229 and Junkers Ju 388.

The MK 108 was also fitted to night fighters in an unusual installation, called "Schräge Musik" (German colloquialism: "jazz",[1] literally "awkward music" or "slanted music"). In this configuration, the cannons were mounted in the fuselage, aiming upwards and slightly forwards at an oblique (18 to 30 degree) angle, depending on fitment and aircraft. This allowed the night fighter to attack bombers, often undetected, by approaching from underneath the enemy aircraft - many British heavy bombers had neither weapons on the ventral fuselage nor windows for vision. This installation was so effective that discovery and news of its adoption was much slower than usual in reaching British night-bombing forces, as there were rarely any survivors from the attacks to report the new threat. This system was fitted to some versions of the He 219 Uhu, late-model Bf 110 night fighters, Junkers Ju 88 & 388 and the Dornier Do 217N model. It was also fitted more rarely to the (prototype) Focke-Wulf Ta 154 and Fw 189 along with the planned, two-seat Me 262B-2 jet night-fighter. In the latter case this produced a jet fighter with six MK108 cannons - with the fitment of the projected mass-produced, mid-VHF band FuG 218 radar.

Related designs

MK 112
Production history
No. built15 (prototypes)
Mass300 kilograms (660 lb)
275 kilograms (606 lb) (improved version)
Length2,000 millimetres (79 in)

Cartridge55 × 175RB mm
Caliber55 mm
ActionBlowback operation
Rate of fire300 rounds/min
Muzzle velocity594 m/s (1,950 ft/s)

The MK 108 mechanism was scaled up in the MK 112 cannon, using a 55×175RB cartridge. The MK 112 was intended to be fitted in pairs in the nose of Me 262 fighters, with 25 rounds per gun, and also in the nose of later models of the Arado Ar 234 for night fighter duty. Underwing mounts for the twin-engined, high-speed Dornier Do 335 heavy fighter were in development as well. The gun was not finished in time to see operations in World War II.[2] Only 15 prototypes were built; of these 10 were delivered for tests and 5 were kept at the factory for improvements based on expected feedback. Of the ten guns delivered for tests, seven were of an early model, weighing 300 kg (660 lb), and three were lighter at 275 kg (606 lb) — these were both significantly lighter than the slightly smaller, 50-mm calibre, 21-round armed Bordkanone-series BK 5 cannon, itself weighing some 540 kg (1,190 lb). The MK 112's projectile was supposed to weigh 1.5 kg (3.3 lb); of these, 420 g (15 oz) were reserved for the explosive.[3] The US captured some of these prototypes and knowledge gleaned from them was incorporated into the experimental US 57 mm T78 autocannon, but this did not see production either.[2]

See also


  1. ^ Gustin, Emmanuel. "Upward firing guns." The WWII Fighter Gun Debate, 1999. Retrieved: 18 June 2012.
  2. ^ a b Anthony G. Williams (2002). Rapid Fire: The Development of Automatic Cannon, Heavy Machine-Guns and Their Ammunition for Armies, Navies and Air Forces. Airlife. p. 169. ISBN 978-1-84037-435-3.
  3. ^ George Chinn 1951, The Machine Gun: Development During World War II and Korean Conflict by the United States and their Allies of Full Automatic Machine Gun Systems and High Rate of Fire Power Driven Cannon, Volume III, Parts VIII and IX., p. 627

External links

Arado E.381

The Arado E.381 (Kleinstjäger – "smallest hunter") was a proposed parasite fighter aircraft. Conceived by Arado Flugzeugwerke in December 1944 for Germany's Luftwaffe during World War II, the E.381 was to have been carried aloft by and launched from an Arado Ar 234 "mother" aircraft. It would then have activated its rocket engine, which would have propelled it to attack Allied (mainly American and British) bombers. Development was cancelled due to lack of funds and official support.There were three proposed variants; each had fuel capacity for only two target runs, after which the pilot would have been required to glide without power to a landing on underbelly skids. To survive close pursuits, the E.381 was designed with the narrowest frontal cross-section possible to increase its chances of surviving shots from the front. This also forced the pilot to lie in a prone position. The cross-section was 0.45 square meters (4.8 sq ft), or approximately a quarter of the cross-section of the Messerschmitt Bf 109.

Arado E.581-4

The Arado E.581-4 was a German flying wing bomber project. It had three landing gears, and an unusually low fuselage.


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Hans Blohm C.M. (born 1927), photographer and author

Linn Blohm (born 1992), Swedish handball player for IK Sävehof and the Swedish national team

Robert Blohm (born 1948), American and Canadian investment banker, economist and statistician, professor in China's Central University of Finance and Economics

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Dornier P 256

The Dornier P 256 was a turbojet night fighter proposed by Dornier for the Luftwaffe toward the end of the Second World War. It was never built.

Focke-Wulf Ta 254

The Focke-Wulf Ta 254 was a proposed German development of the Ta 154 fighter, to have been produced by Focke-Wulf.

Focke-Wulf Volksjäger

The Focke-Wulf Volksjäger, meaning "People's Fighter" in German, was a German emergency fighter project for the Luftwaffe. It was designed by Focke-Wulf industries towards the end of World War II as part of the defense effort against the devastating Allied bombing raids.

MK 103 cannon

The Rheinmetall-Borsig MK 103 ("MK" - Maschinenkanone) was a German 30 mm caliber autocannon that was mounted in German combat aircraft during World War II. Intended to be a dual purpose weapon for anti-tank and air-to-air fighting, it was developed from the MK 101. Compared to the MK 101 it was faster firing, and was originally intended to develop a higher muzzle velocity than the MK 101. Unlike the MK 101, the MK 103 used a belt feed, allowing it to potentially carry a larger ammunition load. The MK 103 used electrically-primed rather than percussion-primed ammunition. The operating mechanism differed from the recoil-operated MK 101 in that it used a combination of gas and recoil operation. After firing, gas pressure served to unlock the breech, while barrel recoil was used to cycle the action (eject spent cartridge and load a fresh one).

Because of a combination of lower grade steels and lighter components, the mechanism of the MK 103 was not as strong as the MK 101. To counteract this weakness, HE ammunition with a reduced load of propellant was used, resulting in a loss of about 100 m/s in muzzle velocity compared to the MK 101, but the rate of fire was increased. The MK 103 entered service in 1943 as the main armament of the Hs 129 B-1 ground-attack/tank-destroyer aircraft, mounted on the underside of the fuselage in a conformal gun pod.

The original specification for the MK 103 called for it to fit inside an aircraft's engine mounting (possibly as a Motorkanone, firing through a hollow propeller hub), but it proved to be too large and heavy to fit into small fighters like the Bf 109. If mounted elsewhere, such as in the wing, the asymmetric force of the cannon's recoil tended to yaw the aircraft's nose to one side. The only known usage of the MK 103 in a Motorkanone installation was in the Do 335. A modified version with a reduced-profile barrel, the MK 103M, was developed and possibly tested for use as a Motorkanone cannon on single-engine fighter planes such as the Bf 109K, but probably never saw active service. As a consequence, the MK 103 was largely restricted to the role of an air-to-ground weapon for use against armoured vehicles.

Projectile weights for the MK 103 were 330 g (12 oz)) for the HE/M ammunition and 355 g (12.5 oz)) for APCR ammunition. Armour penetration for APCR 42–52 mm (1.7–2.0 in) / 60° / 300 m (980 ft) or 75–95 mm (3.0–3.7 in) / 90° / 300 m (980 ft).

A limited-production series of the Fw 190A fighter and Fw 190F ground attack fighter (which utilized a particularly strong wing/fuselage design) incorporated two MK 103 cannons, one mounted under each wing in a conformal, gondola-style pod. Later in the war the MK 103 was also used as a ground-based anti-aircraft (AA) weapon, using single or dual mounts. It was also used as a flak autocannon in the Flakpanzer IV "Kugelblitz".

Developed alongside the MK 103 was the lighter MK 108 cannon, which had a shorter barrel and used a modified blow-back operating system. It fired the same projectile, using a smaller cartridge case with less propellant, at a relatively low muzzle velocity. The shorter barrel made it more adaptable, so it saw much greater use.

Messerschmitt Me 309

The Messerschmitt Me 309 was a prototype German fighter, designed in the early years of World War II to replace the Bf 109. Although it had many advanced features, the Me 309's performance left much to be desired and it had so many problems that the project was cancelled with only four prototypes built. The Me 309 was one of two failed Messerschmitt projects intended to replace the aging Bf 109, the other being the Me 209 of 1943.

Messerschmitt P.1095

The Messerschmitt P.1095 was a German military aircraft designed by Rudolf Seitz (not the SS Officer) at the end of 1943. The aircraft used the wings, cockpit, and controls of the Me 262 and the tail surfaces and landing gear of the Me 309. The design was to have been powered by a turbojet engine located under the fuselage, and it was to have been armed with two nose-mounted MK 108 cannon.

Messerschmitt P.1110

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