20-mm self-propelled anti-aircraft gun based on the tank "Crusider" Crusader AA Mk II – Crusader AA Mk III. Self-propelled anti-aircraft installation was created in 1942 for air defense of troops on the march and in places of concentration. The cruiser tank "Crusider" was used as a base. Instead of a tank turret, a lightly armored circular rotation turret with a twin mount of two Oerlikon 20-mm automatic anti-aircraft guns with a barrel length of 120 calibers was mounted on the remaining practically unchanged chassis instead of the tank turret. The thickness of the frontal armor of the hull and turret was 25 mm, the armor of the hull and turret was 12,7 mm. The armor plates of the tower were located at a certain angle to the vertical. The twin installation installed in the turret had a rate of fire of 2 x 450 rounds per minute, a maximum firing range of 7200 m, and an altitude reach of 2000 m. ground targets. This possibility is provided by the presence of two sights: anti-aircraft and for firing at ground targets. The guns had an elevation angle of 890 degrees, a descent angle of 90 degrees. Guiding them to the target was carried out by hydraulic or manual drive. To provide external communications, a radio station was mounted on a self-propelled unit. After the Crusider tank, the chassis of which was used to create a self-propelled gun, was discontinued, it continued to be produced on the chassis of the Cromwell tank.   The development of self-propelled anti-aircraft guns based on the tank "Crusader" began in September 1941. Serial production was launched in 1943 at Moris Motors. Self-propelled anti-aircraft installation was created in 1942 for air defense of troops on the march and in places of concentration. The cruiser tank "Crusider" was used as a base. Instead of a tank turret, a lightly armored circular rotation turret with a twin mount of two Oerlikon 20-mm automatic anti-aircraft guns with a barrel length of 120 calibers was mounted on the remaining practically unchanged chassis instead of the tank turret. The thickness of the frontal armor of the hull and turret was 25 mm, the armor of the hull and turret was 12,7 mm. The armor plates of the tower were located at a certain angle to the vertical. The twin installation installed in the turret had a rate of fire of 450 rounds per minute, a maximum firing range of 7200 m, and an altitude reach of 2000 m. . This possibility is provided by the presence of two sights: anti-aircraft and for firing at ground targets. The guns had an elevation angle of 90 degrees, a descent angle of 9 degrees. Guiding them to the target was carried out by hydraulic or manual drive. To provide external communications, a radio station was mounted on a self-propelled unit. After the Crusider tank, the chassis of which was used to create a self-propelled gun, was discontinued, it continued to be produced on the chassis of the Cromwell tank. Serial modifications: СrusaderAA1 - 40-mm automatic anti-aircraft gun "Bofors" is installed in a tower of circular rotation, open at the top, having the shape of a truncated pyramid. The vertical angle of the gun is from -10° to +70°. To rotate the tower, a hydraulic drive from an auxiliary engine is used. The combat weight is 18 tons, the crew is 3 people, the ammunition load is 160 rounds, the maximum speed is 42 km/h. The hull, power plant, transmission and chassis are borrowed from the base tank. 215 units were made. СrusaderAA2 is a paired installation of 20-mm Oerlikon automatic cannons in a rotating multi-faceted turret open at the top. High-speed horizontal and vertical guidance drive. Turret rotation - from the main engine. Hull, power plant, transmission and chassis - like the base tank. СrusaderAA3 - improved turret, 7,7 mm Vickers machine gun on top of 20 mm cannons. The radio station antenna has been moved to the front of the case. About 600 units of AA2 and AA3 were made. Self-propelled anti-aircraft installations began to be used in hostilities since 1944. In the headquarters companies of tank divisions and brigades there were two ZSUs, and in the headquarters companies of the regiments - six. ZSU were used to cover combat units from the air. However, it quickly became clear that, contrary to expectations, they could not fire on the move. In addition, in the conditions of the dominance of Allied aviation in the air, the ZSU had little work. A small number of these combat vehicles were still in service in 1945. Performance characteristics Combat weight 18 t Dimensions:   length 5890 mm width 2600 mm height 2240 mm Crew 4 person weaponry twin installation of two 20-mm automatic guns "Oerlikon" Ammunition 600 shells Booking:   forehead 52m m brow tower 25,4 mm engine's type carburetor "Naffid-Liberty", type NL III Maximum power 345 hp full speed 48 km / h Power reserve 160 km Sources: M. Baryatinsky. Crusader and others. (Armored collection, 6 - 2005); G.L. Kholyavsky "The Complete Encyclopedia of World Tanks 1915 - 2000"; Yu. F. Katorin. Tanks. Illustrated Encyclopedia; Crusader Cruiser 1939-45 [Osprey – New Vanguard 014]; Chris Henry, British Anti-Tank Artillery 1939-1945.