An anti-aircraft vehicle, also known as a self-propelled anti-aircraft gun (SPAAG) or self-propelled air defense system (SPAD), is a mobile vehicle with a dedicated anti-aircraft capability. Specific weapon systems used include machine guns, autocannons, larger guns, or missiles, and some mount both guns and longer-ranged missiles (e.g. the Pantsir-S1). Platforms used include both trucks and heavier combat vehicles such as armored personnel carriers and tanks, which add protection from aircraft, artillery, and small arms fire for front line deployment. Anti-aircraft guns are usually mounted in a quickly-traversing turret with a high rate of elevation, for tracking fast-moving aircraft. They are often in dual or quadruple mounts, allowing a high rate of fire. In addition, most anti-aircraft guns can be used in a direct-fire role against surface targets to great effect. Today, missiles (generally mounted on similar turrets) have largely supplanted anti-aircraft guns, but they may return as an cheap way to counter unmanned aerial systems (drones). History World War I Anti-aircraft machine guns have long been mounted on trucks, and these were quite common during World War I. A predecessor of the WWII German "88" anti-aircraft gun, the WWI German 77 mm anti-aircraft gun, was truck-mounted and used to great effect against British tanks. The British QF 3 inch 20 cwt was mounted on trucks for use on the Western Front. The British also had a first dedicated anti aircraft weapon, the QF 1-pounder pom-pom. Mounted on a armoured truck titled the Pierce-Arrow armoured AA lorry, which was produced in limited numbers and only seeing service throughout 1915. Inter-war period Between the two World Wars, the United Kingdom developed the Birch gun, a general-purpose artillery piece on an armoured tracked chassis capable of maintaining formation with their current tanks over terrain. The gun could be elevated for anti-aircraft use. Vickers Armstrong also developed a SPAAG based on the chassis of the Vickers Mk.E 6-ton light tank/Dragon, Medium, Mark IV artillery tractor, mounting a Vickers QF-1 "Pom-Pom" gun of 40 mm. About 26 were sold to Siam and saw action as infantry support guns and AA guns during the Franco-Thai war (1940-1941) along with 30 Vickers Mk.E Type B 6-ton tanks. This was probably the first tracked SPAAG manufactured in series. Later the British also developed a version of the Mk.VI Light Tank armed with four machine guns that were known as Light Tank AA Mk.I. And also a twin 15