The 8 in (203 mm) howitzer, which was replaced by the M110 self-propelled howitzer, is a towed weapon developed prior to World War II as a heavy artillery weapon. The weapon uses NATO standard 203mm ammunition, and was used during World War II, in Korea, and in Viet Nam. In NATO service their prime mission was to fire nuclear rounds which have since been phased out of service. Tests of the prototype T3 howitzer began at Aberdeen Proving Ground in 1939 and the howitzer entered service as the 8 in Howitzer M1. After the Second World War the complete weapon was redesignated the Howitzer, Heavy, Towed: 8 in: M115. Variants of the M110 with a longer barrel includethe M110A1 (no muzzle brake) and the M110A2 (fitted with muzzle brake). In most countries the M115 and the M110 have been phased out of service due to short range. The carriage of the 8 in howitzer is also used to mount the 155 mm Gun M1 (Long Tom), which is still in use with some armies. The carriage consists of equilibrator assemblies, elevating and traversing mechanisms, two single-wheel, single-axle heavy limber, two-axle bogie with eight tyres and two trails. Four spades, carried on the trails, are used to emplace the weapon. In recent years some armies have towed the weapon without the limber.