Against sloped armour, the APDS had reduced effectiveness: penetrating 87 mm (3.4 in) and 77 mm (3.0 in) of RHA at 1,000 yd (910 m) and 2,000 yd (1,800 m) respectively, against a plate angled 60 degrees from the normal, this is only 174 mm (6.9 in), and 154 mm (6.1 in) of line of sight penetration. The APDS projectile had a muzzle velocity of 1,465 m/s (4,810 ft/s) and the APDS Mk.3 could penetrate 330 mm (13 in) of RHA at a distance of 1,000 yards (910 m), and 290 mm (11 in) of penetration at 2,000 yards (1,800 m), equating to a line of sight penetration of 330 mm and 290 mm respectively. However, these conventional rounds were rarely used. The 20 pounder's APCBC projectile had an initial muzzle velocity of 1,020 metres per second and could penetrate 210 mm (8.3 in) of rolled homogeneous armour (RHA). ( North Vietnamese tanks did not operate in South Vietnam until later stages of the 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. īetween 19, Mk III Centurions of the Australian Army, equipped with the original 20 pounder, saw action during the Vietnam War. (However, the Panzer 58 was later equipped with the 105 mm L7. One was fitted to a Swiss pre-production Panzer 58, replacing a domestic 90 mm Kanone 1948 gun. ĭuring the development of its successor, the 20 pounder continued in front-line service and was even trialed in other fighting vehicles. 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.

The 100 mm gun wielded by the T-54 was also assessed. Analysis of the T-54's armour suggested that the 20 pounder would be ineffective at penetrating the latest Soviet armour.

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. 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 1954, the original version of the 105 mm was made by re-boring the tube of a 20 pounder barrel. The L7 105 mm tank gun was developed from the 20 pounder. The gun was developed by the Royal Ordnance Factories.Īs fitted to the Charioteer, it ran through two models: 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. It was introduced in 1948 and used in the Centurion main battle tank, Charioteer medium tank, and Caernarvon Mark II heavy tank. 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. This gun is a later model which is fitted with a bore evacuator Charioteer tank equipped with the 20 pounder.