The Fokker-Leimberger was an early example of an externally powered machine gun of Imperial German origin that predated the M134 Minigun. It had 12 barrels and could fire over 7200RPM it had the spent brass ruptured. The weapon was experimented with during World War I until the armistice with the last development example retained by the late A.H.G. Fokker as his personal property. Most probably he transferred this weapon with other personal belongings to the United States until his death in 1939. Its possible the Fokker-Leimberger was discovered for re-evaluation during the development of the M61 Vulcan.
The history of this engine operated weapon goes back to a secret circular with the-then Major Wilhelm Siegert (a Prussian Air Corps inspector) directed to German aircraft and engine suppliers on August 16, 1916. It was pointed out that all current Aircraft Guns suffered from their relation to the demands of land forces. Airborne Firearms should be lightweight, high rates of fire in bursts handling aircraft speeds of over 130MPH and at high altitudes temperatures of -40 degrees celsius, required small space and practical for firing vertically downwards. Siegert suggested operating such weapons mechanically, either by the aero engine or electrical power sources used for the wireless, They should also be multiple barreled. He invited new ideas from firms formerly u trial weapons and other facilities would be made at once.
This very sensible memorandum spawned up a series of engine operated aircraft weapons from the companies of Siemens, Autogen, Szakatz-Gotha, Fokker and some startingly good ideas. None of the guns became operational during the war except the Siemens example which was tried on the Western Front with a victory using it during air combat. There is little doubt that these weapons became effective had the war lasted into 1919.
Fokker and his right-hand armament expert, H.W. Luebbe produced several designs. One had a direct drive by a crank from an MG08 machine gun. The other was the revolutionary Leimberger 12-barrel gun. This was fired soon after the issue of the memorandum above. The barrels, which were mounted within a drum-like rotor, were normal, except for the fact that each breech was half cut-away along the axis of the bore. The matching other half of the breech was formed by a corresponding depression in a second drum-like rotor of smaller diameter which rotated underneath the barrel cylinder. When the two breech halves of these rotating parts joined up, spur-gear like, the barrel concerned attained its firing position with the cartridge in place. The feeding belt with the cartridges were carried right through the split breech of the two rotating elements, much like a chain between sprockets. The cartridges were not extracted, as the spent cases were still in the belt after firing. There was no reciprocating breech block. Firing took place by percussion when the breech closed perfectly (firing pin on swash plate). The gun was therefore extremly simple (as the M61 Vulcan). It was devoid of any reciprocating parts and free from the defects which affected the Maxim MG08. Moreover, it could be fired at any speed. The upper rate of fire was limited soleley by centrifugal stresses and by the time the propellant needed burning.
In air combat, the gun had to be pre-rotated so as to fire at a top rate as soon as the trigger released the cartridge feed. This was necessary since otherwise too much time would be lost accelerating the mechanism. There is no record of ballistic performance, but it would seem that the long calibre-lengths of the barrels might adversley affect the stability of the projectile. There can be little doubt the barrel material had a long life, considering the air-cooling and the low sequence of fire through the individual barrels.
Versions of this rifle calibre gun were fired over 7,200 rounds per minute. The weapon, however suffered from too many jams as the quality of German cartridge-case material had seriously deteriorated, and only too often the cases tore open in the gun.
- Motor Guns-A flashback to 1914-18. Flight, 8 March 1957, Page 313/314