3.7 cm Flak 18/36/37

The 3.7 cm Flak 18/36/37 was a series of anti-aircraft guns produced by Nazi Germany that saw widespread service in the Second World War. The cannon was fully automatic and effective against aircraft flying at altitudes up to 4,200 m. The cannon was produced in both towed and self-propelled versions. Having a flexible doctrine, the Germans used their anti-aircraft pieces in ground support roles as well; 37 mm caliber guns were no exception to that. With Germany's defeat, production ceased and, overall, 37 mm caliber anti-aircraft cannon fell into gradual disuse, being replaced by the Bofors 40 mm gun and later, by 35-mm anti-aircraft pieces produced in Switzerland.

Development

File:Oddziały niemieckie na Riwierze francuskiej (2-351).jpg

3.7 cm Flak 36 mounted on a German armoured truck in 1943

The original 37 mm gun was developed by Rheinmetall in 1935 as the 3.7 cm Flak 18. The cannon had an overall length of 89 calibers (hence the additional designation L/89), which allowed Template:Convert maximum ceiling. The armour penetration was considerable when using dedicated ammunition, at 100 m distance it could penetrate 36 mm of a 60°-sloped armour, and at 800 m distance correspondingly 24 mm. It used a mechanical bolt for automatic fire, featuring a practical rate of fire of about 80 rounds per minute (rpm). The gun, when emplaced for combat, weighed Template:Convert, and complete for transport, including the wheeled mount, Template:Convert.

The Flak 18 was only produced in small numbers, and production had already ended in 1936. Development continued, focusing on replacement of the existing cumbersome dual-axle mount with a lighter single-axle one, resulting in a 3.7 cm Flak 36 that cut the complete weight to Template:Convert in combat and Template:Convert in transport. The gun's ballistic characteristics were not changed, although the practical rate of fire was raised to 120 rpm (180 rpm theoretical). A new, simplified sighting system introduced the next year produced the otherwise-identical 3.7 cm Flak 37. The Flak 37 was known as 37 ITK 37 in Finland.

The Flak 36/37 were the most-produced variants of the weapon.

Tun antiaerian Rheinmetall calibru 37 mm model 1939

In 1938, the Kingdom of Romania acquired the license to locally produce 360 guns, officially known as "Tun antiaerian Rheinmetall calibru 37 mm model 1939" ("37 mm Rheinmetall anti-aircraft cannon model 1939") at the Astra Works in Brașov. By May 1941, 102 guns had been delivered. The production rate was of 6 pieces per month as of October 1942.

Aviation version

File:Bundesarchiv Bild 101I-655-5976-04, Russland, Sturzkampfbomber Junkers Ju 87 G.jpg

Ju 87G with twin BK 3,7 underwing gun pods

The earlier Flak 18 version of the 37mm autoloading gun was adapted for aviation use as the BK 3,7, the lightest-calibre model of the Bordkanone series of heavy caliber cannon used in Luftwaffe aircraft during the war. The BK 3,7 was usually employed for strike against ground targets, or for bomber destroyer duties. Mounted within self-contained gun pods or in conformal gondola-style flat-surface mounted gunpod housings, the BK 3,7 saw use on the Ju 87G panzerknacker ("tank-cracker") version of the Stuka dive bomber as flown with considerable success by Hans-Ulrich Rudel, the Ju 88P-2 and P-3 subtypes, and the Hs 129 B-2/R3 twin-engined strike aircraft.

Similar weapons

The closest Allied counterpart to the 3.7 cm Flak series was the 40 mm Bofors L/60, which was designated the "4 cm Flak 28" in German service. The Bofors fired a larger shell of Template:Convert, as opposed to around Template:Convert, at a slightly higher muzzle velocity of around Template:Convert as opposed to just under Template:Convert. This gave the Bofors an effective ceiling of about Template:Convert compared to Template:Convert for the Flak series. Firing rates for the earlier models were similar, although the Flak 43's improved rates beat the Bofors. The most notable difference is the size and weight of the two weapons; the Bofors weighed just under Template:Convert and required a two-axle trailer, while the earlier Flak models weighed Template:Convert on a single-axle mount, and the Flak 43 reduced this even further to Template:Convert.

The 37 mm automatic air defense gun M1939 (61-K) was the closest Soviet counterpart, firing a shell very similar to the Flak with a similar rate of fire from a gun of generally similar weight and size. The US's 37 mm Gun M1 was similar to the Flak as well, but was considered inferior to the Bofors and saw relatively limited use. The Japanese had nothing similar, their largest AA autocannon being the Type 96 25 mm AT/AA Gun. The Italian counterpart was the Breda Cannone-Mitragliera da 37/54.

Comparison of anti-aircraft guns

Country	Gun Model	RPM	Projectile Weight	Weight of fire per minute
Template:Country data Nazi Germany	3.7 cm Flak 18/36/37	160	Template:Convert	Template:Convert
Template:Country data Nazi Germany	3.7 cm SK C/30	30	Template:Convert	Template:Convert
	Canon de 37 mm Modèle 1925	15–21	Template:Convert	Template:Convert
	Cannone-Mitragliera da 37/54 (Breda)	60–120	Template:Convert	Template:Convert
	37 mm Gun M1	120	Template:Convert	Template:Convert
	37 mm automatic air defense gun M1939 (61-K)	80	Template:Convert	Template:Convert
	QF 2-pounder naval gun	115	Template:Convert	Template:Convert
	Bofors 40 mm gun	120	Template:Convert	Template:Convert

See also

• 3.7 cm Flak 43

Sources

• Gander, Terry and Chamberlain, Peter. Weapons of the Third Reich: An Encyclopedic Survey of All Small Arms, Artillery and Special Weapons of the German Land Forces 1939-1945. New York: Doubleday, 1979 Template:ISBN
• Hogg, Ian. Twentieth-Century Artillery. New York: Barnes & Noble Books, 2000. Template:ISBN Pg.107
• Hogg, Ian V. German Artillery of World War Two. 2nd corrected edition. Mechanicsville, PA: Stackpole Books, 1997 Template:ISBN