Armour-piercing[edit]

British APCBC Shell Mk XXII BNT (circa 1943) forBL 15 inch Mk I naval gun, showingbase fuze

The earliest naval andanti-tankshells had to withstand the extreme shock of punching througharmour plate. Shells designed for this purpose sometimes had a greatly strengthened case with a small bursting charge, and sometimes were solid metal, i.e.shot. In either case, they almost always had a specially hardened and shaped nose to facilitate penetration. This resulted in armour-piercing (AP) projectiles.

A further refinement of such designs improved penetration by adding a softer metal cap to the penetrating nose giving armour-piercing, capped (APC) design. The softer capdampsthe initial shock that would otherwise shatter the round. The best profile for the cap is not the most aerodynamic; this can be remedied by adding a further hollow cap of suitable shape:APCBC(APC + ballistic cap).^[12]

AP shells with a bursting charge were sometimes distinguished by appending the suffix "HE". At the beginning of the Second World War, solid shot AP projectiles were common. As the war progressed, ordnance design evolved so that APHE became the more common design approach foranti-tankshells of 75mm caliber and larger, and more common in naval shell design as well. In modern ordnance, most full caliber AP shells are APHE designs.

Armour-piercing, composite non-rigid[edit]

Armour-piercing, composite non-rigid (APCNR), the British term, but the more common terms aresqueeze-boreandtapered boreand are based on the same projectile design as the APCR - a high density core within a shell of soft iron or other alloy, but it is fired by a gun with a tapered barrel, either a taper in a fixed barrel (Gerlichdesign in German use; original development efforts in the late 1930s in Germany, Denmark and France) or a final added section as in the BritishLittlejohn adaptor. The projectile is initially full-bore, but the outer shell is deformed as it passes through the taper. Flanges or studs are swaged down in the tapered section, so that as it leaves the muzzle the projectile has a smaller overall cross-section.^[13]This gives it better flight characteristics with a higher sectional density and the projectile retains velocity better at longer ranges than an undeformed shell of the same weight. As with the APCR the kinetic energy of the round is concentrated at the core on impact. The initial velocity of the round is greatly increased by the decrease of barrel cross-sectional area toward the muzzle, resulting in a commensurate increase in velocity of the expanding propellant gases. The Germans deployed their initial design as a light anti-tank weapon,2,8 cm schwere Panzerbchse 41, early in the Second World War, and followed on with the4.2 cm Pak 41and7.5 cm Pak 41. Although HE rounds were also put into service, they weighed only 93grams and had low effectiveness.^[14]The British used the Littlejohn squeeze-bore adaptor which could be attached or removed as necessary. The adaptor extended the usefulness of armoured cars and light tanks which could not fit any gun larger than theQF 2 pdr. Although a full range of shells and shot could be used, changing the adaptor in the heat of battle was highly impractical. The APCNR was superseded by the APDS design which was compatible with non-tapered barrels.

High-explosive, anti-tank[edit]

HEATshells are a type ofshaped chargeused to defeat armoured vehicles. They are extremely efficient at defeating plain steel armour but less so against later composite andreactive armour. The effectiveness of the shell is independent of its velocity, and hence the range: it is as effective at 1000 metres as at 100 metres. The speed can even be zero in the case where a soldier simply places a magnetic mine onto a tank's armor plate. A HEAT charge is most effective when detonated at a certain, optimal, distance in front of the target and HEAT shells are usually distinguished by a long, thin nose probe sticking out in front of the rest of the shell and detonating it at the correct distance, e.g.,PIATbomb. HEAT shells are less effective if spun (i.e., fired from a rifled gun).