Editing Armour-piercing ammunition (section)

== History ==
[[File:The photographic history of the Civil War - thousands of scenes photographed 1861-65, with text by many special authorities (1911) (14762466292).jpg|thumb|Steel plates penetrated in tests by naval artillery, 1867]]

The late 1850s saw the development of the [[ironclad warship]], which carried [[wrought iron]] armour of considerable thickness. This armour was practically immune to both the round [[cast-iron]] cannonballs then in use and to the recently developed [[Artillery shell|explosive shell]].

The first solution to this problem was effected by [[William Palliser|Major Sir W. Palliser]], who, with the [[Palliser shot and shell|Palliser shot]], invented a method of hardening the head of the pointed cast-iron shot.<ref name=EB1911>{{cite EB1911 |wstitle=Ammunition |volume=1 |pages=864–875 |first=Henry |last=Seton-Karr |author-link=Henry Seton-Karr}}</ref> By casting the projectile point downwards and forming the head in an iron mold, the hot metal was suddenly chilled and became intensely ''[[Hardening (metallurgy)|hard]]'' (resistant to deformation through a [[Martensite|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 ''[[Toughness|tough]]''<ref name=EB1911/> (resistant to shattering).

These chilled iron shots proved very effective against wrought iron armour but were not serviceable against compound and [[steel]] armour,<ref name=EB1911/> which was first introduced in the 1880s. A new departure, therefore, had to be made, and [[Forging|forged steel]] rounds with points [[Hardening (metallurgy)|hardened]] by water took the place of the Palliser shot. At first, these forged-steel rounds were made of ordinary [[carbon steel]], but as armour improved in quality, the projectiles followed suit.<ref name=EB1911/>

During the 1890s and subsequently, [[Cementation process|cemented]] steel armour became commonplace, initially only on the thicker armour of warships. To combat this, the projectile was formed of steel—forged or cast—containing both [[nickel]] and [[chromium]]. Another change was the introduction of a [[Armor-piercing cap|soft metal cap]] over the point of the shell – so called "Makarov tips" invented by Russian admiral [[Stepan Makarov]]. 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. It could also help penetration from an oblique angle by keeping the point from deflecting away from the armour face.

=== World War I ===
Shot and shell used before and during [[World War I]] were generally cast from special [[chromium]] steel that was melted in pots. They were forged into shape afterward and then thoroughly [[Annealing (metallurgy)|annealed]], the core bored at the rear and the exterior turned up in a [[Lathe (metal)|lathe]].<ref name=EB1911/> The projectiles were finished in a similar manner to others described above. The final, or [[Tempering (metallurgy)|tempering]] treatment, which gave the required hardness/toughness profile (differential hardening) to the projectile body, was a closely guarded secret.<ref name=EB1911/>

The rear cavity of these projectiles was capable of receiving a small bursting charge of about 2% of the weight of the complete projectile; when this is used, the projectile is called a shell, not a shot. 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.<ref name=EB1911/>

=== World War II ===
[[File:BL15inchAPMkXXIIBNTShell1943Diagram.jpg|thumb|British naval [[BL 15 inch Mk I naval gun|15-inch (381 mm)]] capped armour-piercing high explosive shell with ballistic cap (APHECBC), 1943]]
During World War II, projectiles used highly alloyed steels containing [[nickel]]-chromium-[[molybdenum]], although in Germany, this had to be changed to a [[silicon]]-[[manganese]]-chromium-based alloy when those grades became scarce. The latter alloy, although able to be hardened to the same level, was more brittle and had a tendency to shatter on striking highly sloped armour. The shattered shot lowered penetration, or resulted in total penetration failure; for ''armour-piercing high-explosive'' (APHE) projectiles, this could result in premature detonation of the high-explosive filling. Advanced and precise methods of differentially hardening a projectile were developed during this period, especially by the German armament industry. The resulting projectiles change gradually from high hardness (low toughness) at the head to high toughness (low hardness) at the rear and were much less likely to fail on impact.

APHE shells for tank guns, although used by most forces of this period, were not used by the British. The only British APHE projectile for tank use in this period was the ''Shell AP, Mk1'' for the [[Ordnance QF 2 pounder|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. They had been using APHE since the invention of the 1.5% high-explosive Palliser shell in the 1870s and 1880s, and understood the tradeoffs between reliability, damage, percentage of high explosive, and penetration, and deemed reliability and penetration to be most important for tank use. Naval APHE projectiles of this period, being much larger used a bursting charge of about 1–3% of the weight of the complete projectile,<ref name=EB1911/> but in anti-tank use, the much smaller and higher velocity shells used only about 0.5% e.g. [[Panzergranate 39]] with only 0.2% high-explosive filling. This was due to much higher armour penetration requirements for the size of shell (e.g. over 2.5 times calibre in anti-tank use compared to below 1 times calibre for naval warfare). Therefore, in most APHE shells put to anti-tank use the aim of the bursting charge was to aid the number of fragments produced by the shell after armour penetration, the energy of the fragments coming from the speed of the shell after being fired from a high velocity anti-tank gun, as opposed to its bursting charge. There were some notable exceptions to this, with naval calibre shells put to use as anti-concrete and anti-armour shells, albeit with a much reduced armour penetrating ability. The filling was detonated by a rear-mounted delay fuze. The explosive used in APHE projectiles needs to be highly insensitive to shock to prevent premature detonation. The US forces normally used the explosive [[Dunnite|Explosive D]], otherwise known as ammonium picrate, for this purpose. Other combatant forces of the period used various explosives, suitably desensitized (usually by the use of waxes mixed with the explosive).