BK 37

BK 3,7
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 flywheel.
Type	Aircraft mounted auto-cannon
Place of origin	Germany
Service history
In service	1942-1945
Used by	Axis powers
Wars	World War Two
Production history
Manufacturer	Rheinmetall-Borsig
Specifications
Weight	295 kg (650 lb)
Length	3,630 mm (143 in)
Cartridge	37x263
Cartridge weight	APCR 380 g (13 oz), HE 640 g (23 oz), AT 685 g (24.2 oz)
Caliber	37 mm (1.46 in)
Barrels	1
Action	Short Recoil
Rate of fire	160 rpm
Muzzle velocity	1,170–780 metres per second (3,800–2,600 ft/s)
Effective firing range	500 metres (550 yd)

The Bordkanone 3,7 (BK 3,7) English: (on-)board cannon 3,7 was a 3.7 cm (1.46 in) anti-tank/bomber 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 anti-tank or bomber-destroyers: Junkers Ju 87 G-1 and G-2; Henschel Hs 129B-2/R3; Messerschmitt Bf 110G-2/R1-3; Junkers Ju 88P-2 / 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 APCR (Tungsten hard-core) ammunition or high-explosive shells in 37x263B mm caliber at 160 rounds per minute.

BK 3,7 equipped ground attack aircraft were developed for use in the anti-tank role on the Eastern Front in a somewhat desperate 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 various issues (primarily poor accuracy, severe weight penalty making the craft vulnerable to fighters, and a low ammunition capacity), but could be extremely effective when operated by a sufficiently skilled and practised ground-attack pilot (Hans-Ulrich Rudel in his BK 3,7 armed Junkers Ju 87G being the ultimate example).

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 in both anti-tank and bomber destroyer role.