carried a heavy field-gun. The next major advance was the Birch gun (1925), developed for the British motorised warfare experimental brigade (the Experimental Mechanized Force). This mounted a field gun, capable of the usual artillery trajectories and even anti-aircraft use, on a tank chassis. During World War II, most major military powers developed self-propelled artillery vehicles. These had guns mounted on a tracked chassis (often that of an obsolete or superseded tank) and provided an armoured superstructure to protect the gun and its crew. The first British design, "Bishop", carried the 25 pdr gun-howitzer in an extemporised mounting on a tank chassis that severely limited the gun's performance. It was replaced by the more effective Sexton. The Germans built many lightly armoured self-propelled anti-tank guns using captured French equipment (for example Marder I), their own obsolete light tank chassis (Marder II), or ex-Czech chassis (Marder III). These led to better-protected tank destroyers, built on a medium-tank chassis such as the Jagdpanzer IV or the Jagdpanther. Anti-aircraft vehicle The Self-propelled anti-aircraft weapon debuted in WWI. The German 88 mm anti-aircraft gun was truck-mounted and used to great effect against British tanks, and the British QF 3-inch 20 cwt was mounted on trucks for use on the Western Front. Although the Birch gun was a general purpose artillery piece on an armoured tracked chassis, it was capable of elevation for anti-aircraft use. Vickers Armstrong developed one of the first SPAAGs based on the chassis of the Mk.E 6-ton light tank/Dragon Medium Mark IV tractor, mounting a Vickers QF-1 "Pom-Pom" gun of 40 mm. The Germans fielded the Sd.Kfz. 10/4 and 6/2, cargo halftracks mounting single 20 mm or 37 mm AA guns (respectively) by the start of the war. Self-propelled multiple rocket-launcher Rocket launchers such as the Soviet Katyusha originated in the late 1930s. The Wehrmacht fielded self-propelled rocket artillery in World War II – the Panzerwerfer and Wurfrahmen 40 equipped half-track armoured fighting vehicles. Many modern multiple rocket launchers are self propelled by either truck or tank chassis. Cold War By the end of World War II, most modern armies had vehicles to carry infantry, artillery and anti-aircraft weaponry. Most modern AFVs are superficially similar in design to their World War II counterparts, but with significantly better armour, weapons, engines, electronics, and suspension. The increase in the capacity of transport aircraft makes possible and practicable the transport of AFVs by air.