MK 108

MK 108
Two MK 108 autocannons, RAF Museum Cosford (2010)
Type
Place of origin	Nazi Germany
Service history
In service	1943–1945
Used by	Nazi Germany
Wars	World War II
Production history
Designer	Rheinmetall-Borsig
Designed	1940
Manufacturer	Rheinmetall-Borsig
Produced	1943–1945
Specifications
Weight	58 kilograms (128 lb)
Length	1,057 millimetres (41.6 in)
Barrel length	580 millimetres (23 in)
Cartridge	30×90RB mm steel casing
Caliber	30 mm
Action	Advanced Primer Ignition Blowback
Rate of fire	650 rounds/min
Muzzle velocity	540 m/s (1,770 ft/s)

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

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.

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 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.