Armour Piercing Discarding Sabot (APDS)

Armour Piercing Discarding Sabot ammunition was developed by the British for use with the 6-pounder Anti-Tank Gun and well as the 17-pounder as found on the Sherman Firefly.

The first APDS round was developed in the UK and entered British (and consequently, Canadian) service in 1943-44 for both the 6-pdr and 17-pdr guns. The round was developed in response to increasing armour thicknesses on German medium and heavy tanks and the need to upgrade the performance of tank and anti-tank guns. Since tungsten rounds were too heavy if developed as a full bore round to achieve high muzzle velocity, the use of "sabot", a light sheath around the round, was developed. The added surface area at the base of the projectile combined with lower weight provided increased acceleration inside the gun barrel, and once clear of the muzzle, a combination of centripetal and aerodynamic force stripped the sabot off, lowering the drag of the projectile in flight. Penetration power of the round was greatly improved, and the APDS rounds were successful in increasing the ability of Allied guns to defeat German armour.

While the Germans had produced a tapered gun with its arrow round, which provided higher velocity at the expense of heavy barrel wear and rounds which were inaccurate due to instabilities caused by the deformation of the projectile as it was squeezed through the decreasing taper of the barrel, General A.G.L. McNaughton solved the problem by developing a small shell that could be fired by a larger calibre gun.

The difference in calibre was taken up by a light metal or plastic pot in which the round sat, and which acted as a driving band to give the projectile its stabilizing spin. The fore part of the projectile was held in place by a serrated band of three petals. When the round was fired, the high force of gravity broke the serrations, and when the round left the barrel, the spin and air pressure caused the petals to fly to the sides, while a combination of pressure and drag caused the pot to fall away. By such means, a small projectile, such as a 2-pounder shell, fired from a 25-pounder gun would receive a much greater thrust, resulting in significantly increased muzzle velocity and thus greater armour penetration.

Tests with the Super Velocity Discarding Sabot (SVDS) were carried out in France in Sep 1944 by the 3rd Anti-Tank Regiment RCA, and the Sabot projectile was subsequently used against enemy armour with excellent results for the remainder of the war. This type of ammunition, with subsequent improvements, went on to form the main anti-tank ammunition in modern tanks as the 20th Century wound down, with the main difference lying in the size and shape of the sub-calibre projectile and the material used in its construction. Materials used later included Tungsten Carbide and Depleted Uranium.