3.7 cm Flak 18/36/37

Development

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 4800 m maximum ceiling. 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 1750 kg, and complete for transport, including the wheeled mount, 3560 kg.

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 1550 kg in combat and 2400 kg 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

Main article: BK 3,7

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 900 g, as opposed to around 650 g, at a slightly higher muzzle velocity of around 880 m/s as opposed to just under 800 m/s. This gave the Bofors an effective ceiling of about 4900 m compared to 4200 m 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 2000 kg and required a two-axle trailer, while the earlier Flak models weighed 1550 kg on a single-axle mount, and the Flak 43 reduced this even further to 1250 kg.

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

Notes

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
• Hogg, Ian. Twentieth-Century Artillery. New York: Barnes & Noble Books, 2000. Pg.107
• Hogg, Ian V. German Artillery of World War Two. 2nd corrected edition. Mechanicsville, PA: Stackpole Books, 1997

References

1. Ivanov, A.. (2003). "АРТИЛЛЕРИЯ ГЕРМАНИИ ВО ВТОРОЙ МИРОВОЙ ВОЙНЕ (Artilleria Germanyi Vo Vtoroy Mirovoy Voyne)". ОЛМА Медиа Групп.
2. Third Axis - Fourth Ally, pag. 30
3. [https://books.google.com/books?id=MuGsf0psjvcC&dq=flak+43+length&pg=PA168], ''The Encyclopedia of Weapons of World War II'', Chris Bishop, pp. 167-8
4. Hogg, ''German Artillery of World War Two''
5. The armour penetration was considerable when using dedicated''PzGr. 18'' [[cast iron]] [[armour piercing high explosive]] ammunition.
6. Third Axis - Fourth Ally, pag. 75
7. Carruthers, Bob (2012). German Tank Hunters - The Panzerjäger. Archive Media Publishing Ltd. {{ISBN. 978-1781581384.
8. DiGiulian, Tony. "Germany 3.7 cm/83 SK C/30 – NavWeaps".
9. DiGiulian, Tony. "France 37 mm/50 (1.46") Model 1925 and CAIL Model 1933 – NavWeaps".
10. DiGiulian, Tony. "Italy 37 mm/54 (1.5") Models 1932, 1938 and 1939 – NavWeaps".
11. Foss, Christopher. (1977). "Jane's pocket book of towed artillery". Collier.
12. DiGiulian, Tony. "Russia / USSR 37 mm/67 (1.5") 70-K – NavWeaps".
13. DiGiulian, Tony. "United Kingdom / Britain 2-pdr QF Mark VIII – NavWeaps".
14. DiGiulian, Tony. "USA Bofors 40 mm/60 Model 1936 – NavWeaps".