MK 108 cannon
Encyclopedia
The MK 108 was a 30 mm caliber
autocannon
manufactured in Germany
during World War II
by Rheinmetall
-Borsig
for use in aircraft
.
(RLM—Reich Aviation Ministry) in response to a 1942 requirement for a heavy aircraft weapon for use against the Allied
heavy bomber
s 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 high-explosive ammunition to bring down a heavy bomber
such as a B-17 Flying Fortress or B-24 Liberator
and a single hit to down a fighter. In comparison, the otherwise excellent 20 mm MG 151/20
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
.
, 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 cartridges 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 incendiary rounds were also often fitted with a hydrostatic fuse, which detonated when it came in contact with liquid. This was to ensure that the round did not merely explode on the target aircraft's skin, which would cause little damage, but instead penetrated and exploded when it came into contact with fuel or coolant inside the fuel tank
s or radiator
s respectively.
The cannon proved to be very effective and reliable, yet comparatively light, compact and easy to manufacture. These characteristics stem from its simple construction—80% of the weapon was made from stamped parts, and the number of moving parts was kept to a bare minimum by using advanced primer ignition blowback (APIB) operation. However, this has some disadvantages, mostly the inability to combine a high ballistic performance with a high rate of fire. The MK 108 was optimized for a high rate of fire.
Otherwise, it was simple to manufacture and maintain, and its compact size and weight as well as its 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, amongst whom the cannon gained a fearsome reputation due to its destructive power.
article for more information). To avoid this, simple blowback guns have to use low-powered cartridges or a very heavy bolt.
In an APIB gun such as the MK 108, this problem was mitigated by using a chamber longer than necessary to hold the cartridge case. When the trigger was released, the bolt was moved forward by a powerful spring. It not only chambered the cartridge but kept pushing it forward, following the case a small distance into the chamber. Cases with a rebated rim were used, so that the extractor claw could hook over the rim and still fit within the chamber. Primer ignition was timed so that the bolt was still moving forward when the propellant ignited. The expanding gases from the fired round then had to stop the bolt, reverse its motion, and expel the bolt again from the rear end of the chamber. Before this happened, most of the gases had escaped via the barrel, dropping the chamber pressure to a safe level. The heavy bolt then continued to move backwards into buffer springs, which pushed the bolt back into battery after a fresh round had been fed.
The APIB principle permits a higher rate of fire and lighter bolt than a simple blowback, but the length and speed of the travel of the bolt within the chamber are limited by the stresses the sliding motion, executed under high gas pressure, puts on the case. To keep these within limits, the bolt needs to be very heavy or the barrel short. The designers for the MK 108 opted for a short barrel, permitting a light bolt and a fairly high rate of fire.
The resulting low muzzle velocity was the MK 108's main shortcoming, with the result that its projectile trajectory
was seriously affected by bullet drop after a comparatively short range—41 m (135 ft) of drop in the first 1,000 m (3,300 ft) of range. The long time of flight and curved trajectory strongly reduced the usefulness of the MK 108 against maneuvering targets like fighters; it was designed for use against bombers. Even against these, attacks had to be pressed home to close range, which was particularly challenging for fast fighters like the Me 262, which risked colliding with the target if their approach speed was too high.
, 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 fighter
s in an unusual installation, called "Schräge Musik
" (German: "Awkward Music", literally "slanting 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, almost always undetected, by approaching from underneath the enemy aircraft - many British heavy bombers had neither weapons on the ventral fuselage or 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 Bf110 night fighters, Junkers 88/388 and the Dornier 217N model. It was also fitted more rarely to the (prototype) Focke Wulf Ta-154 & Fw-189 along with the Me262B-2 model. In the latter case this produced a jet fighter with no less than 6 MK108 cannons - with projected FuG218 radar this would have made a very effective night interceptor.
30 mm caliber
30 mm caliber ammunition is usually used in autocannon. Such ammunition includes NATO standard 30 × 173 mm and 30 × 113 mm and Soviet 30 × 165 mm ammunition widely used around the world....
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...
manufactured in Germany
Nazi Germany
Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...
during 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...
by Rheinmetall
Rheinmetall
Rheinmetall AG is a German automotive and defence company with factories in Düsseldorf, Kassel and Unterlüß. The company has a long tradition of making guns and artillery pieces...
-Borsig
August Borsig
Johann Friedrich August Borsig was a German businessman who founded the Borsig-Werke factory.Borsig was born in Breslau , the son of cuirassier and carpenter foreman Johann George Borsig...
for use in aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
.
Development
The weapon was developed as a private venture by the company in 1940 and was submitted to the ReichsluftfahrtministeriumReich Air Ministry
thumb|300px|The Ministry of Aviation, December 1938The Ministry of Aviation was a government department during the period of Nazi Germany...
(RLM—Reich Aviation Ministry) in response to a 1942 requirement for a heavy aircraft weapon for use against the Allied
Allies of World War II
The Allies of World War II were the countries that opposed the Axis powers during the Second World War . Former Axis states contributing to the Allied victory are not considered Allied states...
heavy bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
s 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 high-explosive ammunition to bring down a heavy bomber
Heavy bomber
A heavy bomber is a bomber aircraft of the largest size and load carrying capacity, and usually the longest range.In New START, the term "heavy bomber" is used for two types of bombers:*one with a range greater than 8,000 kilometers...
such as a B-17 Flying Fortress or B-24 Liberator
B-24 Liberator
The Consolidated B-24 Liberator was an American heavy bomber, designed by Consolidated Aircraft of San Diego, California. It was known within the company as the Model 32, and a small number of early models were sold under the name LB-30, for Land Bomber...
and a single hit to down a fighter. In comparison, the otherwise excellent 20 mm MG 151/20
MG 151 cannon
The MG 151 was a 15 mm autocannon produced by Waffenfabrik Mauser starting in 1940. It was in 1941 developed into the 20 mm MG 151/20 cannon which was widely used on many types of German Luftwaffe fighters, fighter bombers, night fighters, ground attack and even bombers as part of or as...
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
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
. It saw first operational service in late autumn 1943 with the Bf 110G-2
Messerschmitt Bf 110
The Messerschmitt Bf 110, often called Me 110, was a twin-engine heavy fighter in the service of the Luftwaffe during World War II. Hermann Göring was a proponent of the Bf 110, and nicknamed it his Eisenseiten...
bomber destroyers and in the Bf 109G-6/U4
Messerschmitt Bf 109
The Messerschmitt Bf 109, often called Me 109, was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid 1930s...
.
Ammunition
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-piercingArmor-piercing shot and shell
An armor-piercing shell is a type of ammunition designed to penetrate armor. From the 1860s to 1950s, a major application of armor-piercing projectiles was to defeat the thick armor carried on many warships. From the 1920s onwards, armor-piercing weapons were required for anti-tank missions...
, high-explosive and incendiary
Incendiary ammunition
-World War I:One of the first uses of incendiary ammunition occurred in World War I. At the time, phosphorus—the primary ingredient in the incendiary charge—ignited upon firing, leaving a trail of blue smoke. They were also known as 'smoke tracer' for this reason. The effective range of...
. In operation, however, two major ammunition types were used: Minengeschoß
Minengeschoß
The Minengeschoß was a high-capacity autocannon ammunition originally developed in Germany and used in the Luftwaffe's larger caliber aircraft armament during World War II. This new type of high-explosive shell differed from conventional H.E. ammunition in that it had much thinner walls...
("mine-shell") and high-explosive incendiary. The Minengeschoß was made by drawn steel (the same way brass cartridges 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 incendiary rounds were also often fitted with a hydrostatic fuse, which detonated when it came in contact with liquid. This was to ensure that the round did not merely explode on the target aircraft's skin, which would cause little damage, but instead penetrated and exploded when it came into contact with fuel or coolant inside the fuel tank
Fuel tank
A fuel tank is safe container for flammable fluids. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled or released into an engine...
s or radiator
Radiator (engine cooling)
Radiators are used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine....
s respectively.
Construction
Otherwise, it was simple to manufacture and maintain, and its compact size and weight as well as its electrical priming made it ideal for aircraft installation. The cannon's distinctive heavy pounding sound and high rate of fire gave it the nickname
Nickname
A nickname is "a usually familiar or humorous but sometimes pointed or cruel name given to a person or place, as a supposedly appropriate replacement for or addition to the proper name.", or a name similar in origin and pronunciation from the original name....
"pneumatic hammer
Jackhammer
A jackhammer is a pneumatic tool that combines a hammer directly with a chisel that was invented by Charles Brady King. Hand-held jackhammers are typically powered by compressed air, but some use electric motors. Larger jackhammers, such as rig mounted hammers used on construction machinery, are...
" amongst Allied aircrews, amongst whom the cannon gained a fearsome reputation due to its destructive power.
Disadvantages
Normally, gas-operated or delayed-blowback mechanisms are used in automatic weapons of rifle-calibre and larger because the chamber pressure in such weapons would be 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 blowbackBlowback (arms)
Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the propellant charge....
article for more information). To avoid this, simple blowback guns have to use low-powered cartridges or a very heavy bolt.
In an APIB gun such as the MK 108, this problem was mitigated by using a chamber longer than necessary to hold the cartridge case. When the trigger was released, the bolt was moved forward by a powerful spring. It not only chambered the cartridge but kept pushing it forward, following the case a small distance into the chamber. Cases with a rebated rim were used, so that the extractor claw could hook over the rim and still fit within the chamber. Primer ignition was timed so that the bolt was still moving forward when the propellant ignited. The expanding gases from the fired round then had to stop the bolt, reverse its motion, and expel the bolt again from the rear end of the chamber. Before this happened, most of the gases had escaped via the barrel, dropping the chamber pressure to a safe level. The heavy bolt then continued to move backwards into buffer springs, which pushed the bolt back into battery after a fresh round had been fed.
The APIB principle permits a higher rate of fire and lighter bolt than a simple blowback, but the length and speed of the travel of the bolt within the chamber are limited by the stresses the sliding motion, executed under high gas pressure, puts on the case. To keep these within limits, the bolt needs to be very heavy or the barrel short. The designers for the MK 108 opted for a short barrel, permitting a light bolt and a fairly high rate of fire.
The resulting low muzzle velocity was the MK 108's main shortcoming, with the result that its projectile trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
was seriously affected by bullet drop after a comparatively short range—41 m (135 ft) of drop in the first 1,000 m (3,300 ft) of range. The long time of flight and curved trajectory strongly reduced the usefulness of the MK 108 against maneuvering targets like fighters; it was designed for use against bombers. Even against these, attacks had to be pressed home to close range, which was particularly challenging for fast fighters like the Me 262, which risked colliding with the target if their approach speed was too high.
Operational usage
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 109Messerschmitt Bf 109
The Messerschmitt Bf 109, often called Me 109, was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid 1930s...
, Messerschmitt Bf 110
Messerschmitt Bf 110
The Messerschmitt Bf 110, often called Me 110, was a twin-engine heavy fighter in the service of the Luftwaffe during World War II. Hermann Göring was a proponent of the Bf 110, and nicknamed it his Eisenseiten...
, Messerschmitt Me 163
Messerschmitt Me 163
The Messerschmitt Me 163 Komet, designed by Alexander Lippisch, was a German rocket-powered fighter aircraft. It is the only rocket-powered fighter aircraft ever to have been operational. Its design was revolutionary, and the Me 163 was capable of performance unrivaled at the time. Messerschmitt...
, Messerschmitt Me 262
Messerschmitt Me 262
The Messerschmitt Me 262 Schwalbe was the world's first operational jet-powered fighter aircraft. Design work started before World War II began, but engine problems prevented the aircraft from attaining operational status with the Luftwaffe until mid-1944...
, Focke-Wulf Fw 190
Focke-Wulf Fw 190
The Focke-Wulf Fw 190 Würger was a German Second World War single-seat, single-engine fighter aircraft designed by Kurt Tank in the late 1930s. Powered by a radial engine, the 190 had ample power and was able to lift larger loads than its well-known counterpart, the Messerschmitt Bf 109...
, Focke-Wulf Ta 152
Focke-Wulf Ta 152
The Focke-Wulf Ta 152 was a World War II German high-altitude fighter-interceptor designed by Kurt Tank and produced by Focke-Wulf. The Ta 152 was a development of the Focke-Wulf Fw 190 aircraft...
, Focke-Wulf Ta 154
Focke-Wulf Ta 154
|-See also:-External links:*...
, Heinkel He 162
Heinkel He 162
The Heinkel He 162 Volksjäger was a German single-engine, jet-powered fighter aircraft fielded by the Luftwaffe in World War II. Designed and built quickly, and made primarily of wood as metals were in very short supply and prioritised for other aircraft, the He 162 was nevertheless the fastest of...
, Heinkel He 219
Heinkel He 219
The Heinkel He 219 Uhu was a night fighter that served with the German Luftwaffe in the later stages of World War II. A relatively sophisticated design, the He 219 possessed a variety of innovations, including an advanced VHF-band intercept radar...
, Horten Ho 229
Horten Ho 229
The Horten H.IX, RLM designation Ho 229 was a late–World War II prototype fighter/bomber designed by Reimar and Walter Horten and built by Gothaer Waggonfabrik...
and Junkers Ju 388
Junkers Ju 388
The Junkers Ju 388 Störtebeker was a World War II German Luftwaffe multi-role aircraft based on the Ju 88 airframe by way of the Ju 188. It differed from its predecessors in being intended for high altitude operation, with design features such as a pressurized cockpit for its crew...
.
The MK 108 was also fitted to night fighter
Night fighter
A night fighter is a fighter aircraft adapted for use at night or in other times of bad visibility...
s in an unusual installation, called "Schräge Musik
Schräge Musik
Schräge Musik, derived from the German colloquialism for "Jazz Music" was the name given to installations of upward-firing autocannon mounted in night fighters by the Luftwaffe and Imperial Japanese Navy Air Service during World War II, with the first victories for each occurring in May 1943...
" (German: "Awkward Music", literally "slanting 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, almost always undetected, by approaching from underneath the enemy aircraft - many British heavy bombers had neither weapons on the ventral fuselage or 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 Bf110 night fighters, Junkers 88/388 and the Dornier 217N model. It was also fitted more rarely to the (prototype) Focke Wulf Ta-154 & Fw-189 along with the Me262B-2 model. In the latter case this produced a jet fighter with no less than 6 MK108 cannons - with projected FuG218 radar this would have made a very effective night interceptor.