The FLAK 43 was a German made anti-aircraft cannon, which saw an immense level of usage during World War 2. The cannon was fully automatic and effective against aircraft flying at altitudes up to 4200 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, and 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, 35-mm anti-aircraft pieces produced by Switzerland.
The new Flak 43 was a dramatic improvement over the older models. A new gas-operated breech improved the practical firing rate to 150 RPM, while at the same time dropping in weight to 1,250 kg (2,800 lb) in combat and mere 2,000 kg (4,400 lb) in transport. The barrel was shortened to 89 calibres. It was also produced in a twin-gun mount, the 3.7 cm Flakzwilling 43, although this version was considered somewhat unwieldy and top-heavy.
The Flak 37 could be found in some numbers mounted to the ubiquitous Sd.Kfz. 7 or later the schwere Wehrmachtschlepper (sWS), but the newer Flak 43 was almost always used in a mobile mounting. Most famous of these were the converted Panzer IV's, first the "interim" Möbelwagen, and later the Ostwind, which was considered particularly deadly.
Compared to its closest Allied counterpart, the 40 mm Bofors L/60, the Flak 43 had double the rate of fire and was both notably lighter & more compact;  to the Bofors credit it was a slightly more powerful weapon (with greater range, ceiling, and a shorter projectile flight time) which fired a more destructive shell. Large-scale production did not start until 1944 and about 7,216 were produced by end of the war (Zwillings included, each counted as two guns).