Armour-piercing ammunition
As tank armour improved during World War II, anti-vehicle rounds began to use a smaller but dense penetrating body within a larger shell, firing at a very-high muzzle velocity.
Modern penetrators are long rods of dense material like tungsten or depleted uranium (DU) that further improve the terminal ballistics.
[2] By casting the projectile point downwards and forming the head in an iron mold, the hot metal was suddenly chilled and became intensely hard (resistant to deformation through a Martensite phase transformation), while the remainder of the mold, being formed of sand, allowed the metal to cool slowly and the body of the shot to be made tough[2] (resistant to shattering).
At first, these forged-steel rounds were made of ordinary carbon steel, but as armour improved in quality, the projectiles followed suit.
This "cap" increased penetration by cushioning some of the impact shock and preventing the armour-piercing point from being damaged before it struck the armour face, or the body of the shell from shattering.
The final, or tempering treatment, which gave the required hardness/toughness profile (differential hardening) to the projectile body, was a closely guarded secret.
The high-explosive filling of the shell, whether fuzed or unfuzed, had a tendency to explode on striking armour in excess of its ability to perforate.
The only British APHE projectile for tank use in this period was the Shell AP, Mk1 for the 2 pdr anti-tank gun and this was dropped as it was found that the fuze tended to separate from the body during penetration.
Even when the fuze did not separate and the system functioned correctly, damage to the interior was little different from the solid shot, and so did not warrant the additional time and cost of producing a shell version.
[3] Claims for priority of invention are difficult to resolve due to subsequent historic interpretations, secrecy, espionage, and international commercial interest.
[4] Shaped-charge warheads were promoted internationally by the Swiss inventor Henry Mohaupt, who exhibited the weapon before World War II.
The Panzerfaust and Panzerschreck or 'tank terror' gave the German infantryman the ability to destroy any tank on the battlefield from 50–150 m with relative ease of use and training, unlike the UK PIAT.
While cumbersome, the weapon at last allowed British infantry to engage armour at range; the earlier magnetic hand-mines and grenades required them to approach suicidally close.
Early WWII-era uncapped armour-piercing (AP) projectiles fired from high-velocity guns were able to penetrate about twice their calibre at close range (100 m).
At longer ranges (500–1,000 m), this dropped 1.5–1.1 calibres due to the poor ballistic shape and higher drag of the smaller-diameter early projectiles.
In an effort to gain better aerodynamics, AP rounds were given ballistic caps to reduce drag and improve impact velocities at medium to long range.
40 and some Soviet designs resemble stubby arrows), but the projectile is lighter: up to half the weight of a standard AP round of the same calibre.
The kinetic energy of the round is concentrated in the core and hence on a smaller impact area, improving the penetration of the target armour.
The concept of a heavy, small-diameter penetrator encased in light metal was later employed in small-arms armour-piercing incendiary and HEIAP rounds.
[8] 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.
[10] 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 and 1944 by L. Permutter and S. W. Coppock, two designers with the Armaments Research Department.
The penetrator is a pointed mass of high-density material that is designed to retain its shape and carry the maximum possible amount of energy as deeply as possible into the target.
Depleted-uranium penetrators have the advantage of being pyrophoric and self-sharpening on impact, resulting in intense heat and energy focused on a minimal area of the target's armour.
Energy is concentrated by using a reduced-diameter tungsten shot, surrounded by a lightweight outer carrier, the sabot (a French word for a wooden shoe).
This combination allows the firing of a smaller diameter (thus lower mass/aerodynamic resistance/penetration resistance) projectile with a larger area of expanding-propellant "push", thus a greater propelling force and resulting kinetic energy.
The fin-stabilisation allows the APFSDS sub-projectiles to be much longer in relation to its sub-calibre thickness compared to the very similar spin-stabilized ammunition type APDS (armour-piercing discarding sabot).
APFSDS sub-projectiles can thus achieve much higher length-to-diameter ratios than APDS-projectiles, which in turn allows for much higher sub-calibre ratios (smaller sub-calibre to the full-calibre), meaning that APFSDS-projectiles can have an extremely small frontal cross-section to decrease air-resistance, thus increasing velocity, while still having a long body to retain great mass by length, meaning more kinetic energy.
Large calibre (105+ mm) APFSDS projectiles are usually fired from smoothbore (unrifled) barrels, as the fin-stabilization negates the need for spin-stabilization through rifling.
[citation needed] Armour-piercing bombs dropped by aircraft were used during World War II against capital and other armoured ships.
