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Armour-piercing ammunition (AP) is a type of
projectile A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found ...
designed to penetrate armour protection, most often including
naval armour Naval armor refers to the various protections schemes employed by warships. The first ironclad warship was created in 1859, and the pace of armour advancement accelerated quickly thereafter. The emergence of battleships around the turn of the 20t ...
,
body armour Body armour, personal armour (also spelled ''armor''), armoured suit (''armored'') or coat of armour, among others, is armour for human body, a person's body: protective clothing or close-fitting hands-free shields designed to absorb or deflect ...
, and
vehicle armour Military vehicles are commonly armoured (or armored; American and British English spelling differences#-our, -or, see spelling differences) to withstand the impact of Fragmentation (weaponry), shrapnel, bullets, Shell (projectile), shells, Rocke ...
. The first, major application of armour-piercing projectiles was to defeat the thick armour carried on many
warship A warship or combatant ship is a naval ship that is used for naval warfare. Usually they belong to the navy branch of the armed forces of a nation, though they have also been operated by individuals, cooperatives and corporations. As well as b ...
s and cause damage to their lightly armoured interiors. From the 1920s onwards, armour-piercing weapons were required for
anti-tank warfare Anti-tank warfare refers to the military strategies, tactics, and weapon systems designed to counter and destroy enemy armored vehicles, particularly tanks. It originated during World War I following the first deployment of tanks in 1916, and ...
. AP rounds smaller than 20 mm are intended for lightly armoured targets such as body armour,
bulletproof glass Bulletproof glass, ballistic glass, transparent armor, or bullet-resistant glass is a strong and optically transparent material that is particularly resistant to penetration by projectiles, although, like any other material, it is not completel ...
, and lightly armoured vehicles. As tank armour improved during
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, anti-vehicle rounds began to use a smaller but dense penetrating body within a larger shell, firing at a very-high
muzzle velocity Muzzle velocity is the speed of a projectile (bullet, pellet, slug, ball/ shots or shell) with respect to the muzzle at the moment it leaves the end of a gun's barrel (i.e. the muzzle). Firearm muzzle velocities range from approximately t ...
. Modern penetrators are long rods of dense material like
tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...
or
depleted uranium Depleted uranium (DU), also referred to in the past as Q-metal, depletalloy, or D-38, is uranium with a lower content of the fissile isotope Uranium-235, 235U than natural uranium. The less radioactive and non-fissile Uranium-238, 238U is the m ...
(DU) that further improve the terminal ballistics.


Penetration

In the context of weaponry, ''penetration'' is the ability of a weapon or projectile to pierce into or through an obstacle. It depends on the specific properties of the bullet, the obstacle, and the angle of impact. The speed of the projectile is particularly important, even in the case of the same kinetic energy.


History

The late 1850s saw the development of the
ironclad warship An ironclad was a steam-propelled warship protected by steel or iron armor constructed from 1859 to the early 1890s. The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells. The firs ...
, which carried
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...
armour of considerable thickness. This armour was practically immune to both the round
cast-iron Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...
cannonballs then in use and to the recently developed explosive shell. The first solution to this problem was effected by Major Sir W. Palliser, who, with the Palliser shot, invented a method of hardening the head of the pointed cast-iron shot. 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'' (resistant to shattering). These chilled iron shots proved very effective against wrought iron armour but were not serviceable against compound and
steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
armour, which was first introduced in the 1880s. A new departure, therefore, had to be made, and forged steel rounds with points hardened by water took the place of the Palliser shot. At first, these forged-steel rounds were made of ordinary
carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...
, but as armour improved in quality, the projectiles followed suit. During the 1890s and subsequently, 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 Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
and
chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...
. Another change was the introduction of a 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 World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
were generally cast from special
chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...
steel that was melted in pots. They were forged into shape afterward and then thoroughly annealed, the core bored at the rear and the exterior turned up in a
lathe A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, threading and turning, with tools that are applied to the w ...
. The projectiles were finished in a similar manner to others described above. The final, or tempering treatment, which gave the required hardness/toughness profile (differential hardening) to the projectile body, was a closely guarded secret. 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.


World War II

During World War II, projectiles used highly alloyed steels containing
nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
-chromium-
molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...
, although in Germany, this had to be changed to a
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
-
manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
-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 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, 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 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).


Projectile composition and construction


Cap and ballistic cap

Cap
suffix In linguistics, a suffix is an affix which is placed after the stem of a word. Common examples are case endings, which indicate the grammatical case of nouns and adjectives, and verb endings, which form the conjugation of verbs. Suffixes can ca ...
es (C, BC, CBC) are traditionally only applied to AP, SAP, APHE and SAPHE-type projectiles (see below) configured with caps, for example "APHEBC" (armour-piercing high explosive ballistic capped), though sometimes the HE-suffix on capped APHE and SAPHE projectiles gets omitted (example: APHECBC > APCBC). If fitted with a tracer, a "-T" suffix is added (APC-T).


Penetrator and filling


Armour-piercing non-solid shells

An armour-piercing projectile must withstand the shock of punching through armour plating. Projectiles designed for this purpose have a greatly strengthened body with a specially hardened and shaped nose. One common addition to later projectiles is the use of a softer ring or cap of metal on the nose known as a penetrating cap, or armour-piercing cap. This lowers the initial shock of impact to prevent the rigid projectile from shattering, as well as aiding the contact between the target armour and the nose of the penetrator to prevent the projectile from bouncing off in glancing shots. Ideally, these caps have a blunt profile, which led to the use of a further thin aerodynamic cap to improve long-range
ballistics Ballistics is the field of mechanics concerned with the launching, flight behaviour and impact effects of projectiles, especially weapon munitions such as bullets, unguided bombs, rockets and the like; the science or art of designing and acceler ...
. Armour-piercing shells may contain a small explosive charge known as a "bursting charge". Some smaller- calibre armour-piercing shells have an inert filling or an incendiary charge in place of the bursting charge.


APHE/SAPHE

''Armour-piercing high-explosive'' (''APHE'') shells are armour-piercing shells containing an explosive filling, which were initially termed "shell", distinguishing them from non-explosive "shot". This was largely a matter of British usage, relating to the 1877 invention of the first of the type, the Palliser shell with 1.5% high explosive (HE). By the start of World War II, armour-piercing shells with bursting charges were sometimes distinguished by the suffix "HE"; APHE was common in
anti-tank Anti-tank warfare refers to the military strategies, tactics, and weapon systems designed to counter and destroy enemy armored vehicles, particularly tanks. It originated during World War I following the first deployment of tanks in 1916, and ...
shells of 75 mm calibre and larger, due to the similarity with the much larger naval armour-piercing shells already in common use. As the war progressed, ordnance design evolved so that the bursting charges in APHE became ever smaller to non-existent, especially in smaller calibre shells, e.g. Panzergranate 39 with only 0.2% high-explosive filling. The primary projectile types for modern anti-tank warfare are discarding-sabot
kinetic energy penetrator A kinetic energy penetrator (KEP), also known as long-rod penetrator (LRP), is a type of ammunition designed to penetrate vehicle armour using a flechette-like, high- sectional density projectile. Like a bullet or kinetic energy weapon, this ty ...
s, such as APDS. Full-calibre armour-piercing shells are no longer the primary method of conducting anti-tank warfare. They are still in use in artillery above 50 mm calibre, but the tendency is to use ''semi-armour-piercing high-explosive'' (''SAPHE'') shells, which have less anti-armour capability but far greater anti-materiel and anti-personnel effects. These still have ballistic caps, hardened bodies and base fuzes, but tend to have far thinner body material and much higher explosive contents (4–15%). Common terms (and acronyms) for modern armour-piercing and semi-armour-piercing shells are: *''HEI-BF'' – High-explosive incendiary (base
fuze In military munitions, a fuze (sometimes fuse) is the part of the device that initiates its function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fu ...
) *''SAPHE'' – Semi-armour-piercing high-explosive *''SAPHEI'' – Semi-armour-piercing high-explosive incendiary *''SAPHEI-T'' – Semi-armour-piercing high-explosive incendiary tracer


HEAT

''High-explosive anti-tank'' (''HEAT'') shells are a type of shaped charge used to defeat armoured vehicles. They are very efficient at defeating plain steel armour but less so against later composite and
reactive armour Reactive armour is a type of vehicle armour used in protecting vehicles, especially modern tanks, against shaped charges and hardened kinetic energy penetrators. The most common type is ''explosive reactive armour'' (ERA), but variants include ...
. The effectiveness of such shells is independent of velocity, and hence the range: it is as effective at 1000 metres as at 100 metres. This is because HEAT shells do not lose penetrating ability over distance. The speed can even be zero in the case where a soldier places a magnetic mine onto a tank's armour plate. A HEAT charge is most effective when detonated at a certain, optimal distance in front of a target and HEAT shells are usually distinguished by a long, thin nose probe protruding in front of the rest of the shell and detonating it at a correct distance, e.g., PIAT bomb. HEAT shells are less effective when spun, as when fired from a rifled gun. HEAT shells were developed during World War II as a
munition Ammunition, also known as ammo, is the material fired, scattered, dropped, or detonated from any weapon or weapon system. The term includes both expendable weapons (e.g., bombs, missiles, grenades, land mines), and the component parts of oth ...
made of an explosive shaped charge that uses the Munroe effect to create a very high-velocity particle stream of metal in a state of superplasticity, and used to penetrate solid
vehicle armour Military vehicles are commonly armoured (or armored; American and British English spelling differences#-our, -or, see spelling differences) to withstand the impact of Fragmentation (weaponry), shrapnel, bullets, Shell (projectile), shells, Rocke ...
. HEAT rounds caused a revolution in anti-tank warfare when they were first introduced in the later part of World War II. One infantryman could effectively destroy any extant tank with a handheld weapon, thereby dramatically altering the nature of mobile operations. During World War II, weapons using HEAT warheads were known as having a ''hollow charge'' or ''shaped charge'' warhead. Claims for priority of invention are difficult to resolve due to subsequent historic interpretations, secrecy, espionage, and international commercial interest. Shaped-charge warheads were promoted internationally by the Swiss inventor Henry Mohaupt, who exhibited the weapon before World War II. Before 1939, Mohaupt demonstrated his invention to British and French ordnance authorities. During the war, the French communicated the technology to the U.S. Ordnance Department, who then invited Mohaupt to the US, where he worked as a consultant on the
bazooka The Bazooka () is a Man-portable anti-tank systems, man-portable recoilless Anti-tank warfare, anti-tank rocket launcher weapon, widely deployed by the United States Army, especially during World War II. Also referred to as the "stovepipe", th ...
project. By mid-1940, Germany had introduced the first HEAT round to be fired by a gun, the 7.5 cm fired by the Kw.K.37 L/24 of the
Panzer IV The IV (Pz.Kpfw. IV), commonly known as the Panzer IV, is a German medium tank developed in the late 1930s and used extensively during the Second World War. Its ordnance inventory designation was Sd.Kfz. 161. The Panzer IV was the most numer ...
tank and the Stug III self-propelled gun (7.5 cm Gr.38 Hl/A, later editions B and C). In mid-1941, Germany started producing HEAT rifle grenades, first issued to
paratrooper A paratrooper or military parachutist is a soldier trained to conduct military operations by parachuting directly into an area of operations, usually as part of a large airborne forces unit. Traditionally paratroopers fight only as light infa ...
s and by 1942 to regular army units. In 1943, the ''Püppchen'', '' Panzerschreck'' and '' Panzerfaust'' were introduced. The Panzerfaust and Panzerschreck or 'tank terror' gave the German infantryman the ability to destroy any tank on the battlefield from 50 to 150 m with relative ease of use and training, unlike the UK PIAT. The first British HEAT weapon to be developed and issued was a rifle grenade using a -inch (63.5 mm) cup launcher on the end of the barrel; the British No. 68 AT grenade issued to the British army in 1940. By 1943, the PIAT was developed; a combination of a HEAT warhead and a
spigot mortar A mortar today is usually a simple, lightweight, man-portable, muzzle-loaded cannon, consisting of a smooth-bore (although some models use a rifled barrel) metal tube fixed to a base plate (to spread out the recoil) with a lightweight bipod ...
delivery system. 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. During World War II, the British referred to the Munroe effect as the ''cavity effect on explosives''.


Armour-piercing solid shots

Armour-piercing solid shot for cannons may be simple, or composite, solid projectiles but tend to also combine some form of incendiary capability with that of armour-penetration. The incendiary compound is normally contained between the cap and penetrating nose, within a hollow at the rear, or a combination of both. If the projectile also uses a tracer, the rear cavity is often used to house the tracer compound. For larger-calibre projectiles, the tracer may instead be contained within an extension of the rear sealing plug. Common abbreviations for solid (non-composite/hardcore) cannon-fired shot are; ''AP'', ''AP-T'', ''API'' and ''API-T''; where "T" stands for "tracer" and "I" for "incendiary". More complex, composite projectiles containing explosives and other ballistic devices tend to be referred to as armour-piercing shells.


AP

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 January 1942 a process was developed by Arthur E. Schnell for 20 mm and 37 mm armour piercing rounds to press bar steel under 500 tons of pressure that made more even "flow-lines" on the tapered nose of the projectile, which allowed the shell to follow a more direct nose first path to the armour target. Later in the conflict, APCBC fired at close range (100 m) from large-calibre, high-velocity guns (75–128 mm) were able to penetrate a much greater thickness of armour in relation to their calibre (2.5 times) and also a greater thickness (2–1.75 times) at longer ranges (1,500–2,000 m). In an effort to gain better aerodynamics, AP rounds were given
ballistic cap Armour-piercing, capped, ballistic capped (APCBC) is a type of configuration for armour-piercing ammunition introduced in the 1930s to improve the armour-piercing capabilities of both Naval gun, naval and anti-tank guns. The configuration consi ...
s to reduce drag and improve impact velocities at medium to long range. The hollow ballistic cap would break away when the projectile hit the target. These rounds were classified as armour-piercing ballistic capped (APBC) rounds. Armour-piercing, capped projectiles had been developed in the early 1900s, and were in service with both the British and German fleets during World War I. The shells generally consisted of a nickel steel body that contained the burster charge and was fitted with a hardened steel nose intended to penetrate heavy armour. Striking a hardened steel plate at high velocity imparted significant force to the projectile and standard armour-piercing shells had a tendency to shatter instead of penetrating, especially at oblique angles, so shell designers added a
mild steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...
cap to the nose of the shells. The more flexible mild steel would deform on impact and reduce the shock transmitted to the projectile body. Shell design varied, with some fitted with hollow caps and others with solid ones. Since the best-performance penetrating caps were not very aerodynamic, an additional
ballistic cap Armour-piercing, capped, ballistic capped (APCBC) is a type of configuration for armour-piercing ammunition introduced in the 1930s to improve the armour-piercing capabilities of both Naval gun, naval and anti-tank guns. The configuration consi ...
was later fitted to reduce drag. The resulting rounds were classified as armour-piercing capped ballistic capped (APCBC). The hollow ballistic cap gave the rounds a sharper point which reduced drag and broke away on impact.Popular Science, December 1944, pg 126
illustration at bottom of page on working principle of APCBC type shell


SAP

''Semi-armour-piercing'' (''SAP'') shot is a solid shot made of
mild steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...
(instead of high-carbon steel in AP shot). They act as low-cost ammunition with worse penetration characteristics to contemporary high carbon steel projectiles.


APCR/HVAP

''Armour-piercing composite rigid'' (''APCR'') in British
nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. (The theoretical field studying nomenclature is sometimes referred to as ''onymology'' or ''taxonymy'' ). The principl ...
, ''high-velocity armour-piercing'' (HVAP) in US nomenclature, alternatively called "hard core projectile" () or simply "core projectile" (), is a projectile which has a core of high-density hard material, such as
tungsten carbide Tungsten carbide (chemical formula: ) is a carbide containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in in ...
, surrounded by a full-bore shell of a lighter material (e.g., an
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
alloy). However, the low sectional density of the APCR resulted in high
aerodynamic drag In fluid dynamics, drag, sometimes referred to as fluid resistance, is a force acting opposite to the direction of motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers, two solid surfaces, or b ...
. Tungsten compounds such as tungsten carbide were used in small quantities of inhomogeneous and discarded sabot round, but that element was in short supply in most places. Most APCR projectiles are shaped like the standard APCBC round (although some of the German ''Pzgr.'' 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 lighter weight allows a higher muzzle velocity. 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. To prevent shattering on impact, a shock-buffering cap is placed between the core and the outer ballistic shell as with APC rounds. However, because the round is lighter but still the same overall size it has poorer ballistic qualities, and loses velocity and accuracy at longer ranges. The APCR was superseded by the APDS, which dispensed with the outer light alloy shell once the round had left the barrel. The concept of a heavy, small-diameter penetrator encased in light metal was later employed in small-arms armour-piercing incendiary and HEIAP rounds.


APCNR/APSV

''Armour-piercing, composite non-rigid'' (''APCNR'') in British
nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. (The theoretical field studying nomenclature is sometimes referred to as ''onymology'' or ''taxonymy'' ). The principl ...
, alternatively called "flange projectile" () or less commonly "armour-piercing super-velocity", is a sub-calibre projectile used in
squeeze bore A squeeze bore, alternatively taper-bore, cone barrel or conical barrel, is a weapon where the internal gun barrel, barrel diameter progressively decreases towards the muzzle (firearms), muzzle, resulting in a reduced final internal diameter. Thes ...
weapons (also known as "tapered bore" weapons) – weapons featuring a barrel or barrel extension which taperes towards the muzzle – a system known as the Gerlich principle. This projectile design is very similar to the APCR-design - featuring a high-density core within a shell of soft iron or another alloy - but with the addition of soft metal
flange A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of a steel beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer o ...
s or studs along the outer projectile wall to increase the projectile diameter to a higher caliber. This caliber is the initial full-bore caliber, 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. 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 of 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 Panzerbüchse 41'', early in
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, and followed by the 4.2 cm Pak 41 and 7.5 cm Pak 41. Although HE rounds were also put into service, they weighed only 93 grams and had low effectiveness. The German taper was a fixed part of the barrel. In contrast, 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 be upgraded with any gun larger than the QF 2 pdr. Although a full range of shells and shot could be used, changing an adaptor during a battle is usually impractical. The APCNR was superseded by the APDS design which was compatible with non-tapered barrels.


APDS

An important armour-piercing development was the ''armour-piercing discarding sabot'' (''APDS''). An early version was developed by engineers working for the French Edgar Brandt company, and was fielded in two calibres (75 mm/57 mm for the 75 mm Mle1897/33 anti-tank gun, 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 and 1944 by L. Permutter and S. W. 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 An anti-tank gun is a form of artillery designed to destroy tanks and other armoured fighting vehicles, normally from a static defensive position. The development of specialized anti-tank munitions and anti-tank guns was prompted by the appearance ...
and later in September 1944 for the QF-17 pdr anti-tank gun. The idea was to use a stronger and denser penetrator material with smaller size and hence less drag, to allow increased impact velocity and armour penetration. The armour-piercing concept calls for more penetration capability than the target's armour thickness. 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. Generally, the penetration capability of an armour-piercing round increases with the projectile's kinetic energy, and with concentration of that energy in a small area. Thus, an efficient means of achieving increased penetrating power is increased velocity for the projectile. However, projectile impact against armour at higher velocity causes greater levels of shock. Materials have characteristic maximum levels of shock capacity, beyond which they may shatter, or otherwise disintegrate. At relatively high impact velocities, steel is no longer an adequate material for armour-piercing rounds. Tungsten and tungsten alloys are suitable for use in even higher-velocity armour-piercing rounds, due to their very high shock tolerance and shatter resistance, and to their high melting and boiling temperatures. They also have very high density. Aircraft and tank rounds sometimes use a core of
depleted uranium Depleted uranium (DU), also referred to in the past as Q-metal, depletalloy, or D-38, is uranium with a lower content of the fissile isotope Uranium-235, 235U than natural uranium. The less radioactive and non-fissile Uranium-238, 238U is the m ...
. Depleted-uranium penetrators have the advantage of being
pyrophoric A substance is pyrophoric (from , , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylb ...
and self-sharpening on impact, resulting in intense heat and energy focused on a minimal area of the target's armour. Some rounds also use
explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...
or incendiary tips to aid in the penetration of thicker armour. High explosive incendiary/armour piercing ammunition combines a
tungsten carbide Tungsten carbide (chemical formula: ) is a carbide containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in in ...
penetrator with an incendiary and explosive tip. 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. Once outside the barrel, the sabot is stripped off by a combination of
centrifugal force Centrifugal force is a fictitious force in Newtonian mechanics (also called an "inertial" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It appears to be directed radially away from the axi ...
and aerodynamic force, giving the shot low drag in flight. For a given calibre, the use of APDS ammunition can effectively double the anti-tank performance of a gun.


APFSDS

''Armour-piercing fin-stabilized discarding sabot'' (''APFSDS'') in English
nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. (The theoretical field studying nomenclature is sometimes referred to as ''onymology'' or ''taxonymy'' ). The principl ...
, alternatively called "arrow projectile" or "dart projectile" (, , ), is a
saboted A sabot (, ) is a supportive device used in firearm/artillery ammunitions to fit/patch around a projectile, such as a bullet/slug or a flechette-like projectile (such as a kinetic energy penetrator), and keep it aligned in the center of the barrel ...
sub-calibre high-sectional density projectile, typically known as a long rod penetrator (LRP), which has been outfitted with fixed fins at the back end for ballistic-stabilization (so called aerodynamic drag stabilization). 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). Projectiles using spin-stabilization ( longitudinal axis rotation) requires a certain mass-ratio between length and diameter (calibre) for accurate flight, traditionally a length-to-diameter ratio less than 10 (more for higher density projectiles). If a spin-stabilized projectile is made too long it will become unstable and tumble during flight. This limits how long APDS sub-projectiles of can be in relation to its sub-calibre, which in turn limits how thin the sub-projectile can be without making the projectile mass too light for sufficient
kinetic energy In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...
(range and penetration), which in turn limits how
aerodynamic Aerodynamics () is the study of the motion of atmosphere of Earth, air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an ...
the projectile can be (smaller calibre means less air-resistance), thus limiting
velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...
, etc., etc. To get away from this, APFSDS sub-projectiles instead use aerodynamic drag stabilization (no longitudinal axis rotation), by means of fins attached to the base of the sub-projectile, making it look like a large metal arrow. 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 Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...
, while still having a long body to retain great mass by length, meaning more
kinetic energy In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...
. Velocity and kinetic energy both dictates how much range and penetration the projectile will have. This long thin shape also has increased sectional density, in turn increasing penetration potential. Large calibre (105+ mm) APFSDS projectiles are usually fired from
smoothbore A smoothbore weapon is one that has a barrel without rifling. Smoothbores range from handheld firearms to powerful tank guns and large artillery mortars. Some examples of smoothbore weapons are muskets, blunderbusses, and flintlock pistols. ...
(unrifled) barrels, as the fin-stabilization negates the need for spin-stabilization through
rifling Rifling is the term for helical grooves machined into the internal surface of a firearms's barrel for imparting a spin to a projectile to improve its aerodynamic stability and accuracy. It is also the term (as a verb) for creating such groov ...
. Basic APFSDS projectiles can traditionally not be fired from rifled guns, as the immense spinning caused by the rifling damages and destroys the fins of the projectile, etc. This can however be solved by the use of "slipping driving bands" on the sabot ( driving bands which rotates freely from the sabot). Such ammunition was introduced during the 1970s and 1980s for rifled high-calibre tank guns and similar, such as the Western Royal Ordnance L7 and the Eastern D-10T. However, as such guns have been taken out of service since the early 2000s onwards, rifled APFSDS mainly exist for small- to medium-calibre (under 60 mm) weapon systems, as such mainly fire conventional full-calibre ammunition and thus need rifling. APFSDS projectiles are usually made from high-density metal alloys, such as
tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...
heavy alloys (WHA) or
depleted uranium Depleted uranium (DU), also referred to in the past as Q-metal, depletalloy, or D-38, is uranium with a lower content of the fissile isotope Uranium-235, 235U than natural uranium. The less radioactive and non-fissile Uranium-238, 238U is the m ...
(DU); maraging steel was used for some early Soviet projectiles. DU alloys are cheaper and have better penetration than others, as they are denser and self-sharpening. Uranium is also
pyrophoric A substance is pyrophoric (from , , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylb ...
and may become opportunistically incendiary, especially as the round shears past the armour exposing non-oxidized metal, but both the metal's fragments and dust contaminate the battlefield with toxic hazards. The less toxic WHAs are preferred in most countries except the US and Russia.


Aerial bombs

Armour-piercing bombs dropped by aircraft were used during
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
against
capital Capital and its variations may refer to: Common uses * Capital city, a municipality of primary status ** Capital region, a metropolitan region containing the capital ** List of national capitals * Capital letter, an upper-case letter Econom ...
and other armoured ships. Among the bombs used by the
Imperial Japanese Navy The Imperial Japanese Navy (IJN; Kyūjitai: Shinjitai: ' 'Navy of the Greater Japanese Empire', or ''Nippon Kaigun'', 'Japanese Navy') was the navy of the Empire of Japan from 1868 to 1945, Potsdam Declaration, when it was dissolved followin ...
in the
attack on Pearl Harbor The attack on Pearl HarborAlso known as the Battle of Pearl Harbor was a surprise military strike by the Empire of Japan on the United States Pacific Fleet at Naval Station Pearl Harbor, its naval base at Pearl Harbor on Oahu, Territory of ...
were armour-piercing bombs, modified from naval shells, which succeeded in sinking the battleship . The ''
Luftwaffe The Luftwaffe () was the aerial warfare, aerial-warfare branch of the before and during World War II. German Empire, Germany's military air arms during World War I, the of the Imperial German Army, Imperial Army and the of the Imperial Ge ...
s PC 1400 armour-piercing bomb and the derived
Fritz X Fritz X was a German guided anti-ship glide bomb used during World War II. Developed alongside the Henschel Hs 293, ''Fritz X'' was one of the first precision guided weapons deployed in combat. ''Fritz X'' was a nickname used both by Allied an ...
precision-guided bomb were able to penetrate of armour. The ''Luftwaffe'' also developed a series of bombs propelled by rockets to assist in penetrating the armour of ships and similar targets.


Small arms

Armour-piercing rifle and pistol cartridges are usually built around a penetrator of
hardened steel The term hardened steel is often used for a plain-carbon steel, medium or high carbon steel that has been given heat treatment and then quenching followed by tempering (metallurgy), tempering. The quenching results in the formation of metastable ma ...
,
tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...
, or
tungsten carbide Tungsten carbide (chemical formula: ) is a carbide containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in in ...
, and such cartridges are often called "hard-core bullets". Rifle armour-piercing ammunition generally carries its hardened penetrator within a
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
or
cupronickel Cupronickel or copper–nickel (CuNi) is an alloy of copper with nickel, usually along with small quantities of other metals added for strength, such as iron and manganese. The copper content typically varies from 60 to 90 percent. ( Monel is a n ...
jacket, similar to the jacket which would surround
lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
in a conventional projectile. Upon impact on a hard target, the copper case is destroyed, but the penetrator continues its motion and penetrates the target. Armour-piercing ammunition for pistols has also been developed and uses a design similar to the rifle ammunition. Some small ammunition, such as the FN 5.7mm round, is inherently capable of piercing armour, being of a small calibre and very high velocity. The entire projectile is not normally made of the same material as the penetrator because the physical characteristics that make a good penetrator (i.e. extremely tough, hard metal) make the material equally harmful to the barrel of the gun firing the cartridge.


Defense

Most modern
active protection system An active protection system (APS) is a system designed to actively prevent certain anti-tank weapons from destroying a vehicle. Countermeasures that either conceal the vehicle from or disrupt the guidance of an incoming guided missile threat are ...
s (APS) are unlikely to be able to defeat full-calibre AP rounds fired from a large-calibre anti-tank gun, because of the high mass of the shot, its rigidity, short overall length, and thick body. The APS uses fragmentation warheads or projected plates, and both are designed to defeat the two most common anti-armour projectiles in use today: HEAT and
kinetic energy penetrator A kinetic energy penetrator (KEP), also known as long-rod penetrator (LRP), is a type of ammunition designed to penetrate vehicle armour using a flechette-like, high- sectional density projectile. Like a bullet or kinetic energy weapon, this ty ...
. Defeating HEAT projectiles can occur by damaging or detonating their explosive filling, or by damaging a shaped charge liner or fuzing system. Defeating kinetic energy projectiles can occur by inducing changes in yaw or pitch or by fracturing the rod.


See also

* Panzergranate 39 *
Raufoss Mk 211 The Raufoss Mk 211 is a .50 BMG (12.7×99mm NATO) multi-purpose Anti-materiel rifle, anti-material high-explosive incendiary/armor-piercing ammunition projectile produced by Nammo under the model name ''NM140 MP''. It is commonly referred to as ' ...


Notes


References


Bibliography

* *


External links

*{{YouTube, c=UCxV8JseLCWxRwLVd1ykivvg, SY Simulations
Armour piercing projectile
Naval artillery Projectiles Vehicle armour