Ordnance QF 20-pounder

The Ordnance QF 20 pounder (known as 20 pounder, 20 pdr or simply 20-pr) was a British 84 mm (3.307 inch) tank gun. It was introduced in 1948 and used in the Centurion main battle tank, Charioteer medium tank, and Caernarvon Mark II heavy tank. After the 20 pounder gun was found to have inadequate performance against the Soviet T-54, the gun was mostly replaced in service by the larger calibre 105 mm L7 gun.

The gun was developed by the Royal Ordnance Factories.

As fitted to the Charioteer, it ran through two models:

The L7 105 mm tank gun was developed from the 20 pounder. In 1954, the original version of the 105 mm was made by re-boring the tube of a 20 pounder barrel.

The gun was fitted predominantly to the Centurion tank, first seeing action in 1950 with British Army units during the Korean War and Suez Crisis (1956).

In 1956, detailed intelligence on the then-new Soviet T-54A main battle tank was obtained by the British military, after Hungarian rebels drove to the British embassy in Budapest, during the Hungarian Revolution of 1956. Analysis of the T-54's armour suggested that the 20 pounder would be ineffective at penetrating the latest Soviet armour. The 100 mm gun wielded by the T-54 was also assessed. The Centurion's earliest combat experiences and intelligence on Soviet armour and tank guns led to development of the 105 mm L7 tank gun, which was designed to fit specifically into the turret mountings of the 20 pounder, facilitating retrofitting to existing tanks.

During the development of its successor, the 20 pounder continued in front-line service and was even trialed in other fighting vehicles. One was fitted to a Swiss pre-production Panzer 58, replacing a domestic 90 mm Kanone 1948 gun. (However, the Panzer 58 was later equipped with the 105 mm L7.)

Between 1968 and 1971, Mk 5/1 Centurions of the Australian Army, equipped with the original 20 pounder, saw action during the Vietnam War. In the context of counterinsurgency operations in South Vietnam, the 84 mm ammunition of the 20 pounder was considered suitable for the armoured fire support role. (North Vietnamese tanks did not operate in South Vietnam until later stages of the war.)