The Bordkanone 5 (lit. "on-board cannon 5"), or BK 5 for short, was a 50mm calibre autocannon developed by the Germans in WWII specifically for use against Allied heavy bomber planes, especially the Boeing B-17 used by the U.S. Army Air Force.
History[]
In 1943, Rheinmetall was given the contract to adapt the 5cm KwK 39 tank gun, used by the Panzer III tank, for aerial use in the Messerschmitt Me 410 bomber destroyer.
The weapons were installed as Umrüst-Bausätze ("Factory Modification") 4 in the Me 410 A-1/U4, and experimentally, in two Me 262 A-1a/U4 jet fighter prototypes (though these were not used operationally), as the MK 214, which used the same caliber, was not yet available.
An experimental fitment of the BK 5 in an undernose Bola (or "dustbin") mount on a small number of Heinkel He 177A-3 heavy bombers was part of a small force of the bombers that was given the task of suppressing enemy flak on the Eastern Front near Stalingrad early in the Winter of 1942-43 as the A-3/Rüstsatz 5 version, allegedly nicknamed the Stalingradtyp ("Stalingrad type").
Approximately 300 BK 5s were manufactured and it saw limited action, most notably in the Me 410 A-1a/U4 planes that served with the II. Gruppe of Zerstörergeschwader 26 (ZG 26). It was also mounted on the Junkers Ju 88 P-4 night attack aircraft. Intended for long-range shots, the cannon was given a telescopic sight in addition to the Me 410's standard Revi C12C gunsight, in order to make it easier to take long-range shots from outside a bomber's defensive perimeter, as a sort of a "stand-off" weapon system. This, however, proved to be more of a hindrance than a help in the turning fights, in which the Me 410s had often found themselves when engaged by enemy fighters, as the maneuvering targets easily escaped from the telescopic sight's small field of view. This forced them to use the normal sights instead. Since the BK 5 was almost useless against such small, nimble targets, the use of the telescopic sight was unnecessary in these situations regardless.
When installed on the Me 262, with the muzzle protruding well past the nose of the fighter, the weapon was found to be prone to jamming. If fired at nighttime, the muzzle flash tended to temporarily blind the pilot's night vision.
When Reich Marshal Hermann Göring was captured and questioned on May 10th, 1945, he mentioned the BK 5 experiments, translated as follows:
"You might find around Germany some jet airplanes equipped with anti-tank guns. Don't blame me for such monstrosities. This was done on the explicit orders of the Führer. Hitler knew nothing about the air. He may have known about the Army or Navy, but absolutely nothing about the air. He even considered the Me-262 to be a bomber and he insisted it should be called a bomber."
Design Details[]
The BK 5 features a 60 calibre-long, recoil-operated hydropneumatic recuperation system and semi-automatic breech. This means that in every shot, the entire barrel recoil together. In the last millimeter of the travel back, the chamber is opened and extract the used casing, cocking the action and leaving it ready to insert the next round. Once the new round is inserted, the breech is automatically closed and the weapon is ready to fire.
The barrel in the recoil movement engaged a series of electric switches and mechanical levers. Those were in charge to command a rammer, an extractor and the mechanism to turn the closed belt.
This mechanism was in charge to insert the used casing back in the belt and to introduce a fresh cartridge, and the weapon was fired just a moment after the breech was closed. The 2,400 kg recoil of the weapon was alleviated by a hydraulic damper. Pneumatic power came from two large compressed air bottles.
Ammunition was fed into the weapon from the left-hand side by a 22-round closed belt.
Gallery[]
