Bk 37 Bordkanone

The Bordkanone BK 37 ((on-)board cannon 37) was a 37mm anti-tank/bomber autocannon based on the earlier 37 mm Flak 18 made by Rheinmetall. It was mounted on World War II Luftwaffe aircraft such as the anti-tank or bomber-destroyer versions of the Junkers Ju 87D-3 and G-2, Henschel Hs 129B-2/R3, Messerschmitt Bf 110G-2/R1-3, and others. The cannon could be attached under the wings or fuselage of the aircraft as a self-contained gun pod with a 12-round magazine. It fired APCR (Tungsten hard core) ammunition or high explosive shells in 37x263B mm caliber at 160 rounds per minute.

Manufacturer: Rheinmetall Borsig
Designer: Rheinmetall Borsig
Designed: N/A
Produced: N/A
Action: Recoil
Caliber: 37mm
Weight: 295 kg (650 lb)
Length: 3.63 m (11 ft 11 in)
Cartridge: 37 mm x 263 mm
Rate of fire: 160 rpm
Muzzle velocity: 1,170 to 780 m/s (3,836 to 2,557 ft/s)
Projectile weight: APCR 380 g, HE 640 g, AT 685 g

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.

Bk 37 Bordkanone being serviced on the wing of a Junkers Ju 87G.
[Source: Bundesarchiv]

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.