BL 5.5 inch gun

In January 1939 a specification was issued for a gun no heavier than 5.5 tons to replace the 6 inch 26 cwt howitzers in use with most medium batteries. For the desired range of 16,000 yards (15 km) ballistic studies recommended making a new calibre of 5.5 inches. The Asbury interrupted screw breechblock initially featured a semi-automatic firing mechanism used on naval guns, which often malfunctioned in the field and thus had to be replaced with a simpler design from WWI field artillery, while the complex hydropneumatic equilibrators had to be swapped for heavier but cheaper and less finicky spring ones. The first units were equipped in UK in the summer of 1941 and in North Africa a year later, 20 guns equipped British and Free French batteries at El Alamein. Subsequently, it also equipped Canadian, Australian, South African, Polish and Indian regiments, and after the war, it was also used by New Zealand. In the Second World War the normal organization was a regiment of 16 guns organized into two batteries. The 5.5 was retained in service after the war. It was used by the Royal Artillery on operations in Korea, South Arabia and Borneo. It was probably used by the Indian Army in wars against Pakistan, and was used by the Pakistan Army against India in the mountains of Kashmir during the Kargil War of 1999. The South African Defence Force used it extensively in the early stages of the South African Border War, including Operation Savannah, calling it the G2. Approximately 72 are still held in reserve by the South African Army. In British post-war service it also replaced the BL 4.5-inch medium field gun. When 6-gun batteries were introduced in the late 1950s, medium regiments had 18 guns and the third battery in each field regiment was equipped with 5.5 inch guns instead of 25-pounder guns. It remained in UK service with Territorial Army regiments until 1980 and in Australian service until replaced by the M198 in about 1984. The UK replacement for 5.5 inch was the FH-70 155 mm towed howitzer, in service as the L121. The last 5.5 rounds were fired in the UK in 1995. In use, the 5.5 was generally towed by the AEC Matador artillery tractor. From the 1950s in British service, the 5.5 was typically towed by an AEC Militant Mk 1 6x6 truck and subsequently the FV 1103 Leyland Martian 6x6 Medium Artillery Tractor. All 5.5-inch guns were manufactured in the UK.

Initially, the 5.5 inch gun fired a 100-pound (45 kg) shell, using four charges in two cartridges to give a maximum range table muzzle velocity of 1,675 feet per second (511 m/s) and a maximum range of 16,200 yards (14,800 m). In 1944 an 82-pound (37 kg) shell was introduced along with Charge Super giving a maximum muzzle velocity of 1,950 feet per second (590 m/s) and a range of 18,100 yards (16,600 m) yards. The new lighter shell contained 1.5 pounds (0.68 kg) more explosive and gradually replaced the older, heavier shell. In addition to high explosive rounds, there were several types of chemical shells weighing between 90 and 98 pounds (41 and 44 kg) and 100-pound (45 kg) 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.

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 casemate. The chassis was reversed, with the enclosed fighting compartment at the rear and the engine, previously at the rear, now at the front. Two prototypes were built, one of which survives and is being restored. The FV300 Series was intended to include a 5.5-inch self-propelled, the FV305. However, it was cancelled before a prototype could be built.

Australia Fort Lytton Military Museum, Brisbane. National Military Vehicle Museum Edinburgh, South Australia. Finland Museo Militaria, Hämeenlinna France Arromanches-les-Bains, Normandy − Musee du Debarquement. Ranville, Normandy − Memorial Pegasus. Falaise − Memorial des civils dans la guerre. India Southern Command Hospital, Pune. Regiment of Artillery Museum, Nashik Road. Italy Caserma "Cesare Battisti", in Meran. Namibia Namibian Army's 4 Artillery Brigade still operationally fields the guns. Netherlands Overloon War Museum. New Zealand National Army Museum, Waiouru. United Kingdom Royal Artillery Museum. Shropshire Regiment Museum, Shrewsbury Castle. Three guns displayed on a roundabout adjacent to MoD Donnington, Telford. Imperial War Museum Duxford. Outside 47 Regt Royal Artillery lines Larkhill. Outside 203 (Elswick) Battery Royal Artillery lines, Blyth, Northumberland. Newhaven Fort.