Ammunition type designed to penetrate armourArmour-piercing ammunition* **Top left:** Solid shot armour-piercing projectiles stuck in armour plate
* **Top right:** Projectile penetration animation
* **Lower left:** Perforated 110 mm (4,3 in) armour plate, penetrated by 105 mm (4,1 in) armour-piercing solid shot projectile
* **Lower right:** Diagram of capped armour-piercing shell:  
• **1.** – Ballistic cap hoặc armour-piercing cap  
• **2.** – Steel alloy kinetic energy penetrator  
• **3.** – Desensitized high explosive bursting charge  
• **4.** – Base-fuse (set with delay to explode inside the target)  
• **5.** – Bourrelet (front) and driving band (rear)

**Armour-piercing ammunition** (**AP**) hay là **đạn xuyên giáp** là một loại đạn được thiết kế để xuyên phá vỏ giáp bảo vệ trên thiết giáp hạm, giáp cá nhân, xe thiết giáp.

Ứng dụng chủ yếu của đạn xuyên giáp là dùng để xuyên thủng lớp giáp dày của các tàu chiến thiết giáp hạm và gây ra những tổn thất bên trong cho các tàu này. Từ những năm 1920s, vũ khí xuyên giáp được cho là bắt buộc trong chống tăng. Các đạn xuyên giáp có cỡ nhỏ hơn 20 mm được sử dụng để đối phó với các mục tiêu bọc thép hạng nhẹ, giáp cá nhân.

Do giáp xe tăng ngày càng được cải tiến trong Chiến tranh thế giới lần thứ 2, các loại đạn xuyên giáp bắt đầu được thiết kế nhỏ hơn nhưng cường độ và độ cứng để xuyên thép lớn hơn, đồng thời sơ tốc đầu nòng cũng cao hơn. Các thanh xuyên hiện nay cấu tạo từ thanh dài vật liệu có tỉ trọng lớn như tungsten hay uranium nghèo (DU) giúp cải thiện hơn nữa đặc tính của đường đạn.

Lịch sử
-------

Các tấm thép bị xuyên trong các thử nghiệm đạn pháo Hải quân, 1867
Cuối những năm 1850s, Hải quân các nước bắt đầu đưa vào trang bị thiết giáp hạm, có lớp vỏ bọc thép dày. Lớp giáp này vô hiệu hóa các đạn bi sắt và cả đạn mang thuốc nổ mạnh.

Major Sir W. Palliser là người đầu tiên đưa ra giải pháp về đạn xuyên phá được lớp giáp dày, qua việc phát minh lý thuyết của tăng cứng đầu đạn bi sắt. Nhờ đúc các viên đạn theo chiều hướng xuống và tạo thành một đầu đạn, kim loại nóng chảy sẽ được tôi và trở nên cứng hơn, trong khi phần còn lại của vật đúc sẽ tạo thành trong khuôn làm bằng cát, giúp kim loại được làm nguội chậm dần và giúp thân viên đạn tạo thành *tough*.

Những viên đạn bi sắt sau khi được tôi có hiệu suất rất tốt chống lại giáp làm bằng sắt nhưng không có hiệu quả với giáp phức hợp và giáp thép, được đưa ra vào năm 1880s. Do đó các nhà thiết kế thay đổi hoàn toàn hướng thiết kế, và đạn thép với đầu đạn được dập và được làm cứng bởi nước đã được sử dụng trong súng Palliser. Ban đầu, những viên đạn được làm bằng thép các bon nhưng do giáp xe thiết giáp ngày càng tốt lên, nên đạn chống tăng cũng phải phát triển hơn.

Trong những năm 1890s và sau đó, giáp thép thấm các bon trở nên phổ biến, ban đầu chỉ để gia cố thêm cho tàu chiến. Để đối đầu với các mục tiêu như vậy, đạn pháo được làm từ thép-dập hoặc đúc-có pha thêm nickel và chromium. Một cải tiến nữa là sự ra đời của mũ kim loại mềm trên chóp đạn, còn gọi là "Makarov tips" được phát minh bởi Đô đốc người Nga Stepan Makarov. Mũ này làm tăng khả năng đâm xuyên của đạn do làm yếu đi va chạm và ngăn tổn hại đầu mũi xuyên giáp của đạn trước khi nó chạm tới bề mặt giáp. Đồng thời mũ kim loại mềm giúp tăng độ xyên ở góc nghiêng do ngăn viên đạn bị trượt đi khỏi bề mặt giáp.

### Chiến tranh thế giới I

Đạn pháo được sử dụng trước và trong World War I thường được làm từ thép đúc chromium (không gỉ). Thép được dập tạo hình và sau đó được tôi, thép sẽ được khoan lỗ ở đầu và được xử lý trên máy tiện. Đạn pháo cũng được chế tạo tương tự như vậy. Ở bước cuối cùng là xử lý nhiệt, giúp cho đạn có đủ độ cứng cần thiết, công nghệ này là một yếu tố bí mật của các nước chế tạo vũ khí.

Lỗ phía sau của đạn pháo có khả năng nạp một lượng nhỏ thuốc phóng, khoảng 2% trọng lượng của đạn. Đạn được nạp thuốc nổ mạnh, có hoặc không có ngòi nổi, và sẽ nổ khi va vào vỏ giáp xuyên thủng vỏ giáp.

### Chiến tranh thế giới II

Đạn pháo xuyên giáp 15-inch (381 mm) của Hải quân Anh với mũi đạn đạo (APCBC), 1943
Trong thời kỳ chiến tranh thế giới 2, đạn pháo sử dụng thép hợp kim có chứa nickel-chromi-molybden. Trong khi người Đức sử dụng thép hợp kim silicon-manganese-chromi do các nguồn cung kim loại bị hạn chế. Hợp kim thép của Đức, dù có khả năng đạt độ cứng tương đương nhưng giòn hơn và dễ bị gãy khi va chạm vào giáp thép nghiêng, giảm độ xuyên giáp, đối với đạn *armour-piercing high-explosive* (APHE), điều này có thể dẫn đến lượng nổ mạnh bị kích nổ sớm. Các giải pháp thay đổi độ cứng của đạn pháo nâng cao khả năng xuyên giáp của đạn pháo được các nước tiến hành trong suốt cuộc chiến tranh, đặc biệt là người Đức. Kết quả là đạ pháo thay đổi độ cứng từ độ cứng cao ở đầu đạn cho đến độ cứng thấp hơn ở đuôi đạn và đảm bảo phát đạn sao cho viên đạn pháo tiếp xúc tốt với vỏ giáp.

Đạn pháo tăng APHE, dù được sử dụng bởi phần lớn các bên tham chiến trong thời kỳ này, nhưng lại không được quân đội Anh sử dụng. Người Anh chỉ sử dụng một loại đạn APHE duy nhất trong thế chiến là đạn *AP, Mk1* cho súng chống tăng **Ordnance QF 2 pounder** và sau đó nó bị loại bỏ do người Anh nhận thấy ngòi nổ có xu hướng bị tách khỏi thân đạn khi đang xuyên qua vỏ giáp. Kể cả khi kíp nổ không bị suy chuyển và toàn bộ hệ thống hoạt động đúng, thì hiệu quả của đạn pháo đối với kíp lái đối phương là quá nhỏ, không phù hợp để tiếp tục dành thời gian để phát triển. 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 configurations| Name | Schematic | Description |
| --- | --- | --- |
| **AP** – Armour-piercing |  | No cap |
| **APC** – Armour-piercing capped |  |   Armour-piercing cap |
| **APBC** – Armour-piercing ballistic capped |  |   Ballistic cap |
| **APCBC** – Armour-piercing capped ballistic capped |  |   Armour-piercing cap  Ballistic cap |

Cap suffixes (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 get omitted (example: APHECBC > APCBC). If fitted with a tracer, a "-T" suffix is added (APC-T).

Projectile configurations (incomplete list)| Name | Schematic | Description |
| --- | --- | --- |
| **AP** – Armour-piercing
**SAP** – Semi-armour-piercing |  |   Solid or hollowed steel body |
| **APHE** – Armour-piercing high explosive
**SAPHE** – Semi-armour-piercing high explosive |  |   Hollowed steel body  Explosive charge |
| **APCR** – Armour-piercing composite rigid |  |   High-density hard material  Deformable metal |
| **APDS** – Armour-piercing discarding sabot |  |   Spin-stabilized penetrator  Sabot |
| **APFSDS** – Armour-piercing fin-stabilized discarding sabot |  |   Fin-stabilized penetrator  Sabot |

Armour-piercing shells
----------------------

An armour-piercing shell must withstand the shock of punching through armour plating. Shells designed for this purpose have a greatly strengthened body with a specially hardened and shaped nose. One common addition to later shells 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 shell from shattering, as well as aiding the contact between the target armour and the nose of the penetrator to prevent the shell 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. 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 shells containing an explosive filling 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"; *armour-piercing high explosive* (*APHE*) was common in anti-tank 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 shell types for modern anti-tank warfare are discarding-sabot kinetic energy penetrators, 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)
* SAPHE – Semi-armour-piercing high-explosive
* SAPHEI – Semi-armour-piercing high-explosive incendiary
* SAPHEI-T – Semi-armour-piercing high-explosive incendiary tracer

### HEAT

Bài chi tiết: High-explosive anti-tank
Animation of a HEAT-shell functioning against armour.
*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. 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 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. 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 Henry Mohaupt's technology to the U.S. Ordnance Department, who invited him to the US, where he worked as a consultant on the bazooka 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 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 paratroopers 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 50–150 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 2 1⁄2-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 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 projectiles (*AP*) 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 caps 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 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 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.

### APCR / HVAP

*Armour-piercing, composite rigid* (*APCR*) in British nomenclature, *high-velocity armour-piercing* (*HVAP*) in US nomenclature, alternatively called "hard core projectile" (tiếng Đức: *Hartkernprojektil*) or simply "core projectile" (tiếng Thụy Điển: *kärnprojektil*), is a projectile which has a core of high-density hard material, such as tungsten carbide, surrounded by a full-bore shell of a lighter material (e.g. an aluminium alloy). However, the low sectional density of the APCR resulted in high aerodynamic drag. 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 a stubby arrow), 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

Bài chi tiết: Squeeze boreXem thêm thông tin: Littlejohn adaptor, 2.8 cm sPzB 41, và 7.5 cm Pak 41
German Armour-Piercing, Composite Non-Rigid projectile
*Armour-piercing, composite non-rigid* (*APCNR*) in British nomenclature, alternatively called "flange projectile" (tiếng Thụy Điển: *flänsprojektil*), is a sub-calibre projectile used in squeeze bore 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 flanges 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, 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

Bài chi tiết: armour-piercing discarding sabot
Swedish armour-piercing discarding sabot projectile, here seen with and without its sabot as well as its internal tungsten core
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 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 also 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 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. Some rounds also use explosive hoặc incendiary tips to aid in the penetration of thicker armour. High explosive incendiary/armour piercing ammunition combines a tungsten carbide 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 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

Bài chi tiết: Armour-piercing fin-stabilized discarding sabot
French armour-piercing, fin-stabilized, discarding sabot projectile
*Armour-piercing fin-stabilized discarding sabot* (*APFSDS*) in English nomenclature, alternatively called "arrow projectile" or "dart projectile" (tiếng Đức: *Pfeil-Geschoss*, tiếng Thụy Điển: *pilprojektil*, tiếng Na Uy: *pilprosjektil*), is a saboted 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 lesser than 10[*cần dẫn nguồn*] (more for higher density projectiles).[*cần dẫn nguồn*] 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 (range and penetration), which in turn limits how aerodynamic the projectile can be (smaller calibre means less air-resistance), thus limiting velocity, 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, while still having a long body to retain great mass by length, meaning more kinetic energy. 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 (unrifled) barrels, as the fin-stabilization negates the need for spin-stabilization through rifling. 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 heavy alloys (WHA) or depleted uranium (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 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.[*cần dẫn nguồn*]

Aerial bombs
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Xem thêm thông tin: Bunker busterArmour-piercing bombs dropped by aircraft were used during World War II against capital and other armoured ships. Among the bombs used by the Imperial Japanese Navy in the attack on Pearl Harbor were 800 kg (1.800 lb) armour-piercing bombs, modified from 41 xentimét (16,1 in) naval shells, which succeeded in sinking the battleship USS *Arizona*. The *Luftwaffe'*s PC 1400 armour-piercing bomb and the derived Fritz X precision-guided bomb were able to penetrate 130 mm (5,1 in) 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
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Bài chi tiết: Armour-piercing bulletArmour-piercing rifle and pistol cartridges are usually built around a penetrator of hardened steel, tungsten, or tungsten carbide, and such cartridges are often called 'hard-core bullets'. Rifle armour-piercing ammunition generally carries its hardened penetrator within a copper hoặc cupronickel jacket, similar to the jacket which would surround lead 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 at 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
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Most modern active protection systems (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. 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.

Xem thêm
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* Panzergranate 39
* Raufoss Mk 211

Ghi chú
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1. ↑  High carbon steel solid shot.
2. ↑  Mild steel solid shot – low cost ammunition with worse penetration characteristics to contemporary high carbon steel projectiles.
3. ↑  Type with a small explosive charge for added post-penetration damage. Designated *APHEI* if filled with a high explosive incendiary charge.
4. ↑  Type with a large explosive charge for major post-penetration damage at the cost of penetration. Designated *SAPHEI* if filled with a high explosive incendiary charge.
5. ↑  In case of the british Littlejohn adaptor, ammunition was designated as *armour-piercing, super-velocity* (*APSV*).

Tham khảo
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1. ↑  "Armour-piercing projectile". *Encyclopedia Britannica* (bằng tiếng Anh). Truy cập ngày 19 tháng 2 năm 2021.
2. 1 2 3 4 5 6 7 8  Seton-Karr, Henry (1911). "Ammunition". Trong Chisholm, Hugh (biên tập). *Encyclopædia Britannica*. **1** (ấn bản 11). Cambridge University Press. tr. 864–875.
3. 1 2  Bonnier Corporation (tháng 2 năm 1945). "The Bazookas Grandfather". *Popular Science*. Bonnier Corporation: 66.
4. ↑  Donald R. Kennedy,'History of the Shaped Charge Effect, The First 100 Years – USA – 1983', Defense Technology Support Services Publication, 1983
5. ↑  Ian Hogg, *Grenades and Mortars' Weapons Book #37, 1974, Ballantine Books*
6. ↑  Western Hills Press, Cheviot Ohio Page 3-B May 30th 1968
7. ↑  Brooks, John (2016). *The Battle of Jutland*. Cambridge: Cambridge University Press. tr. 76–79, 90. ISBN 9781107150140.
8. 1 2  Popular Science, December 1944, pg 126 illustration at bottom of page on working principle of APCBC type shell
9. ↑  Shirokorad, A. B. (Широкорад А. Б.) (2002). *The God of War of the Third Reich (Бог войны Третьего рейха)*. M. AST (М.ООО Издательство АСТ). ISBN 978-5-17-015302-2.
10. ↑  "Shells and Grenades". Old Town, Hemel Hempstead: The Museum of Technology. Lưu trữ bản gốc ngày 16 tháng 10 năm 2010. Truy cập ngày 23 tháng 10 năm 2010.
11. ↑  Jason Rahman (tháng 2 năm 2008). "The 17-Pounder". Avalanche Press. Lưu trữ bản gốc ngày 9 tháng 11 năm 2010. Truy cập ngày 23 tháng 10 năm 2010.
12. ↑  Ogorkiewicz, Richard M (1991). *Technology of tanks*. Jane's Information Group. tr. 76.
13. ↑  Stillwell, Paul (1991). *Battleship Arizona: An Illustrated History*. Annapolis, Maryland: Naval Institute Press. tr. 274–276. ISBN 0-87021-023-8. OCLC 2365447.
14. ↑  Hone, Thomas C. (tháng 12 năm 1977), "The Destruction of the Battle Line at Pearl Harbor", *Proceedings*, United States Naval Institute, quyển 103 số 12, tr. 56–57
15. ↑  Fitzsimons, Bernard, ed. "Fritz-X", in *The Illustrated Encyclopedia of 20th Century Weapons and Warfare* (London: Phoebus, 1978), Volume 10, p. 1037.
16. ↑  "Rocket-Propelled Bomb PC 1000 Rs". *Catalog Of Enemy Ordnance Material*. Office of the Chief of Ordnance. 1 tháng 8 năm 1945. tr. 316.

Bibliography
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* Okun, Nathan F. (1989). "Face Hardened Armor". *Warship International*. **XXVI** (3): 262–284. ISSN 0043-0374.
* Hogg, Ian V. (1985). *The Illustrated Encyclopedia of Ammunition*. Apple Press.

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