Armour-piercing Discarding Sabot - History and Development

History and Development

APDS was developed by engineers working for the French Edgar Brandt company, and was fielded in two calibers (75 mm/57 mm for the Mle1897/33 75 mm anti-tank cannon, 37 mm/25 mm for several 37 mm gun types) just before the French-German armistice of 1940. The Edgar Brandt engineers, having been evacuated to the United Kingdom, joined ongoing APDS development efforts there, culminating in significant improvements to the concept and its realization.The APDS projectile type was further developed in the United Kingdom between 1941-1944 by Permutter and Coppock, two designers with the Armaments Research Department. In mid-1944 the APDS projectile was first introduced into service for the UK’s QF 6 pdr anti-tank gun and later in September 1944 for the 17 pdr anti-tank gun.

The reason for the development of the APDS was the search for anti-tank projectiles with increased penetrating performance. It was known that high impact (terminal) velocity, or a larger diameter projectile would be required to improve penetration. A larger projectile would require a completely new weapon system and may have been too heavy to retrofit onto existing armoured fighting vehicles. Increasing the velocity of the current projectiles was also a problem due to the impact velocity limitations of steel armour-piercing (AP) projectiles, which would shatter at velocities above ~850 m/s when uncapped.

To allow increased impact velocity, a stronger penetrator material was required. The chosen new penetrator material was tungsten carbide (WC), due to its greater hardness and its ability to withstand the greater shock and pressure generated during a higher velocity impact. As the density of WC (~15.7 g/cm³) is twice that of steel (~7.86 g/cm³), such a shot was too heavy at full bore to be accelerated to a sufficient muzzle velocity. To overcome this, a lightweight full diameter carrier shell was developed to sheathe the inner high density core. The name given to this projectile type was the Armor-Piercing Composite Rigid (APCR). The APCR projectile was about half the weight of a standard AP shot, but of the same diameter. Due to the large surface area for the gases to impinge upon the lightweight APCR projectile, it experienced a higher average acceleration in the gun barrel, in turn imparting a higher muzzle velocity. Unfortunately the low sectional density of the APCR resulted in poor carrying power (high aerodynamic drag), losing velocity and penetration rapidly over distance.

To overcome these limitations the British devised a way for the outer sheath to be discarded after leaving the bore. The name given to the discarded outer sheath was the sabot (a French word for a wooden shoe). For APDS projectiles the sabot is also known as a pot, as the sabot resembles a flower pot in shape. The APDS has the advantages of the lightweight projectile with regards to bore acceleration and high muzzle velocity, but does not suffer from the high drag of the APCR in flight.