BK 3,7

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BK 3,7
Bundesarchiv Bild 101I-655-5976-04, Russland, Sturzkampfbomber Junkers Ju 87 G.jpg
Hans-Ulrich Rudel's Junkers Ju 87G, with twin BK 3,7 gun pods attached to the underside of the wings, in Russia, being inertia-started using the hand-cranked internal flywheel.
TypeAircraft mounted auto-cannon
Place of originGermany
Service history
In service1942–1945
Used byAxis powers
WarsWorld War II
Production history
Mass295 kg (650 lb)
Length3,630 mm (143 in)

Cartridge weightAPCR 380 g (13 oz), HE 640 g (23 oz), AT 685 g (24.2 oz)
Caliber37 mm (1.46 in)
ActionShort Recoil
Rate of fire160 rpm
Muzzle velocity1,170–780 metres per second (3,800–2,600 ft/s)
Effective firing range500 metres (550 yd)

The Bordkanone 3,7 (BK 3,7) (on-board cannon 3.7) was a 3.7 cm (1.46 in) anti-tank/bomber autocannon based on the earlier 3.7 cm (1.46 in) Flak 18 made by Rheinmetall. It was mounted on World War II Luftwaffe aircraft such as the Junkers Ju 87 G-1 and G-2; Henschel Hs 129B-2/R3; Messerschmitt Bf 110G-2/R1-3; Junkers Ju 88P-2 or P-3 and others. The cannon could be attached under the wings or fuselage of the aircraft as self-contained gun pods with 12-round magazines. It fired Armour Piercing Composite Rigid (APCR, Tungsten hard-core) ammunition or high-explosive shells in 37 × 263B mm caliber at 160 rounds per minute.

Service history[edit]

BK 3,7 equipped ground attack aircraft were developed for tank hunting on the Eastern Front in an effort to blunt the massive numerical superiority of the Soviet T-34 as the war turned against Germany. The concept was rather rudimentary, suffered from poor accuracy, severe weight penalty making the craft vulnerable to fighters and low ammunition capacity; but could be extremely effective when operated by a sufficiently skilled and practised ground-attack pilot, such as Hans-Ulrich Rudel in his BK 3,7 armed Junkers Ju 87G.

The heavy-calibre auto-cannon-armed series of Junkers Ju 88P twin-engined attack–bomber destroyer aircraft series used twin BK 3,7 cannon, mounted side-by-side in a conformal ventral fuselage gun pod, in its Ju 88P-2 and P-3 versions. The P-3 version only differed through the addition of extra defensive armour. As with other examples of the P-series, the Ju 88P-2 and P-3 were perceived as failures as anti-tank and bomber destroyer aircraft.

In contrast to the previous method (bombs delivered by dive bombing), when the BK 3,7 was employed in a top attack profile against the especially thin upper turret and engine compartment armour of a tank, kills could be achieved with a relatively light and cheap armour-piercing projectile that could be carried in much greater quantities than bombs but would be insufficient to penetrate if fired horizontally from the ground in the normal method.

One of the two surviving Junkers Ju 87s is a G-2 model displayed at the Royal Air Force Museum Cosford; the wings have attachment points for BK 3,7 gun pods but it is not displayed with them fitted.

See also[edit]

Weapons of comparable role, performance and era[edit]



  • Rapid Fire, Anthony G. Williams, Shrewsbury: Airlife Publishing Ltd., 2000. ISBN 1-84037-435-7.

External links[edit]