There have been few radical innovations in the design of German small- or
rifle-caliber machine guns, since these were developed to a high degree of efficiency
before the war. Extensive changes, however, have been made in the design of some of
the larger-caliber aircraft guns. While the 15-mm and the 20-mm types
are still standard aircraft cannon, the Luftwaffe has brought into limited operational
use a 30-mm cannon. It is anticipated that this maybe used on late-model
planes in the near future.
The MG-131 manufactured by Rheinmetal Borsig and the 151 patented by Mauser are among the
most interesting developments in German medium-caliber armament. The accompanying sketches
illustrate these types. These are commonly called machine guns because of their high
rate of fire.
a. The MG-131
The MG-131 is a 13-mm air-cooled, recoil-operated gun, the ammunition being fed in a
disintegrating metal, open-sided link belt, which is both light and flexible. This
gun is distinctive in that the cartridges are detonated electrically. The current is
broken when the gun is pointed toward the tail, wings, etc., and reestablished
when the gun is aimed in the clear. This compact, light gun is of excellent
workmanship and has a bore large enough to make possible the design of
efficient AP and HE ammunition. The theoretical rate of fire is approximately
900 rounds per minute.
b. The MG-151
The MG-151 types (15-mm and 20-mm), found both in fixed and turret mountings, are
notable for the simplicity of their mechanism and their high rate of fire. Although
they are cocked and fired electrically, provision is made for hand cocking for
servicing purposes and in emergencies. Ammunition for these guns is carried in a
disintegrating metal belt similar to that used on the MG-131. A small
electric lamp on the control board automatically lights when the gun is cocked, and
indicates that it is ready to fire. For the 15-mm model the theoretical
rate of fire is about 740 rounds per minute for AP, and 680 rounds per minute for HE. Rates
for the 20-mm version are: AP, 800 rpm; HE, 750 rpm.