less of riveting. The carriages were identical to those used with Ordnance BL 4.5 inch Mark 2. No limber was ever used and the gun fired with its wheels in contact with the ground. During World War II the PL Locks and AC Slide Boxes (a component separate to the gun attached to the bottom and face of the breech block using a rifle-calibre tube insert to initiate firing of the bagged charge) utilising 0.5 inch (12.7 mm) tubes were replaced by PK Locks and Y Slide Boxes using 0.303 inch (7.7 mm) tubes. It used one man laying and had Probert pattern calibrating sights. The dial sight was initially the No 7 but was gradually replaced by the No 9. In the 1960s sights were converted from degrees, minutes and yards to mils and metres. There was no anti-tank telescope. Late in the war a sight adapter was introduced to permit upper register (high angle) fire when the wheels were raised significantly above the level of the spades. The normal gun detachment was 10 men. Ammunition Initially, the 5.5 inch gun fired a shell, using four charges in two cartridges to give a maximum range table muzzle velocity of and a maximum range of . In 1944 an shell was introduced along with Charge Super giving a maximum muzzle velocity of and a range of yards. The new lighter shell contained more explosive and gradually replaced the older, heavier shell. In addition to high explosive rounds, there were several types of chemical shells weighing between and coloured smoke shells; coloured flare shells were also developed. After World War 2, only HE was used. There was no AP (armour-piercing) round for the gun but, in an emergency, gunners were taught to remove the impact fuze and fire the unfused high explosive as an AP substitute. The normal HE fuze was No 117, a percussion, impact fuze that was introduced in 1920 and saw use until the 1960s. In late 1944, the T100 proximity fuze became available. Variants No variants entered service although the UK developed two self-propelled versions to prototype stage. The first in 1945 used the Crusader gun tractor (developed from the Crusader tank to tow 17-pounder anti-tank guns). It was a turretless design with no casemate. The second, FV3805, in the 1950s used a Centurion tank carriage, the gun being in a barbette mounting in a fully enclosed