The 7.5 cm KwK 40' was a German 75 mm Second World War era vehicle-mounted gun, used as the primary armament of the German Panzer IV' medium tank and the Sturmgeschütz III' and Sturmgeschütz IVtank destroyers/assault guns. The design of the KwK 40 was adapted from the similar towed anti-tank gun, the 7.5 cm Pak 40. It replaced the short-barrel 7.5 cm KwK 37 L/24 close-support gun, providing a huge improvement in firepower for mid-war tank designs. It came in two versions, with L/43 and L/48''' barrel lengths, the former used during 1942 and early 1943, and the latter after that point. Along with the Pak 40, the KwK 40/StuK 40 was the most numerous anti-tank gun of the German army, and remained an effective weapon until the war's end.
History
When mounted on a casemate-armored assault gun-designated vehicle instead of a turreted tank, the weapon was called Sturmkanone 40. Both the KwK 40 and StuK 40 were developed from the towed 7.5 cm Pak 40 anti-tank gun. The length of the ammunition used was shortened to allow for easier storage of said ammunition in vehicles the KwK 40 and StuK 40 would be mounted on. The KwK 40 L/43 was mounted on the Panzer IV from April 1942 until June 1943. All 225 vehicles of the Panzer IV F2 mounted the L/43 with a ball shaped muzzle brake. About a 1,000 out of the 1,687 vehicles of the Panzer IV Ausf. G mounted the L/43 with a double baffle muzzle brake. The StuG III with the L/43 gun was designated as Ausf. F. of which only 120 were equipped with the L/43. All StuG III production runs through Ausf. F/8 to G mounted the longer L/48. The 780 original Jagdpanzer IVtank destroyers mounted the Pak 39 variant of the L/48 gun, the later Panzer IV/70 mounted the StuK 42 L/70. The L/48 was 334 mm longer and slightly more powerful than the L/43. L/48 became the standard gun from June 1942 until the end of World War II. The gun was fitted with an electric firing mechanism and the breech operated semi-automatically. Only one-piece ammunition was used.
Following number of vehicles mounted L/48 version from June 1942-April 1945
*Approximately 6,000 vehicles of Ausf. G, H, J out of 8,800 Panzer IV
*7,720 vehicles of StuG III Ausf. G + 246 of Ausf.F + 250 vehicles of StuG III Ausf. F/8
As with the 7.5 cm Pak 40, the muzzle brake of the KwK 40 and StuK 40 went through a series of design changes. Five types of muzzle brakes were used, gradually increasing the area of exposure to the blast. The designs progressed from tubular type double baffle muzzle brakes to single baffle ball shape muzzle brakes, which proved to be insufficient in reducing recoil, followed by a double flange type from May 1943. The front flange and rear disk type was used from March 1944, followed finally by the double disc type.
