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|Type||Aircraft mounted auto-cannon|
|Place of origin||Germany|
|Used by||Axis powers|
|Wars||World War II|
|Mass||295 kg (650 lb)|
|Length||3,630 mm (143 in)|
|Cartridge weight||APCR 380 g (13 oz), HE 640 g (23 oz), AT 685 g (24.2 oz)|
|Caliber||37 mm (1.46 in)|
|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) (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.
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.
- BK 5 cannon : German 50 mm aircraft cannon
- BK 7,5 cannon : German 75 mm aircraft cannon
- COW 37 mm gun : earlier British equivalent
Weapons of comparable role, performance and era
- Vickers S gun : 40-mm British equivalent
- Ho-203 cannon : Japanese equivalent
- Oldsmobile M4 cannon : US equivalent
- Nudelman-Suranov NS-37 : Soviet equivalent
- Nudelman N-37 : Soviet postwar successor
- Ordnance QF 2-pounder
|Wikimedia Commons has media related to BK 3,7.|