With the introduction of armored cruisers, dreadnought warships and later heavily armored battleships, the need arose already in the mid 1860’s to create an ammunition capable of penetrating armor plating. During the following decades a wide variety of armor piercing shells have been created to address the tougher and tougher targets, and to achieve higher velocity (thus higher penetration) without shattering the shell on impact. Today certain AP shell types are still used in anti-tank warfare (especially with the introduction of composite armor), but they have been mostly abandoned by the naval forces due to the lightly armored nature of today’s warships.
AP – Armor Piercing
While the term AP often refers to the whole family of armor piercing rounds, it originally meant a solid metal „shot”, with a hardened case and a pointy tip to help both ballistic characteristics and penetration. They were mostly made out of stainless steel / cast iron, that has been specially tempered after the casting to improve its durability. Their damage output was achieved through fragmentation / ricochet upon penetration. Solid shot projectiles were mainly used up until the beginning of the Second World War.
APHE – Armor Piercing High Explosive
When the armor piercing projectile receives a small bursting charge (typically 2% of the total weight), it is being referred to as a „shell” instead of a „shot”. The main purpose of this charge was to further fragment the shell during an internal explosion. This shell type was developed during the Second World War, and quickly became the standard ammunition for anti-tank warfare. Today most AP shells refer to APHE. (Additional suffixes stand for I – incendiary and T – tracer, creating designations like API, AP-T or API-T.)
APC / APBC / APCBC – Armor Piercing Capped (Ballistic Capped)
The next stepping stone in armor piercing development was to apply a soft metal cap on the tip of the shell (APC), with the aim to cushion the high velocity impact and keep the shell from shattering. This allowed improving penetration by further increasing the shell velocity, which was necessary due to the more and more thick and better sloped armor used in warfare. The downside was the reduced accuracy and range due to worse aerodynamic characteristics of the shell. This was addressed by fitting a streamlined ballistic cap over the APC, to regain accuracy and range, while keeping the improved penetration. These type of shells are referred to as APBC or APCBC.
APCR / HVAP – Armor Piercing Composite Rigid / High Velocity Armor Piercing
The two terms refer to the same ammunition type, APCR being the British term and HVAP being the US term. This was the next step in AP design, as more and more penetration was required on the battlefield. The solution was to produce a lighter shell that allows for higher velocity while using the same caliber. This was achieved by using a smaller, high-density core (typically tungsten carbide) that did the actual work, surrounded by a full bore shell made out of lighter material (like aluminum alloy). To keep the hard core from shattering, a cap was still used (same as with APC ammunition) between the hard core and the outer case. The problem with APCR was though that due to the lighter weight its ballistic qualities suffered, causing it to lose velocity and accuracy over long ranges.
APCNR – Armor Piercing Composite Non Rigid
Trying to solve the long range issue of the otherwise successful APCR ammunition was the APCNR design, that’s often referred to as „squeeze bore” or „tapered bore” solution. This required a special gun barrel that deformed the softer outer shell of the APCNR shell while it left the barrel, giving it better ballistic characteristics. As expected though, having a special barrel for a special ammunition type was not optimal, and another solution was required urgently.
APDS – Armor Piercing Discarding Sabot
The solution came in the form of the APDS design, where the lighter outer case is simply stripped away as it leaves the barrel, allowing the smaller, high-density core to travel trough the air with minimal drag. This solution greatly increased the accuracy and range of the armor piercing shots over large distances. The high density core also became over time longer and thinner to concentrate the kinetic energy over a smaller surface (increasing its potential), but this had its own set of problems, as a long thin rod is aerodynamically unstable, reducing accuracy yet again.
APFSDS – Armor Piercing Fin-Stabilized Discarding Sabot
The current armor piercing evolutionary stepping stone is the APFSDS shell, that fixes the accuracy problems of the early KE (kinetic energy) penetrators by adding a stabilizing fin at the end of the long, thin, high density core, making it look like a metal arrow. This solution is wildly used in today’s modern armored warfare as the armor piercing solution of choice, with the rounds reaching speeds up to 1400 – 1900 m/s. Even the sabots travel at such high speeds that they may fly for several hundred meters at speeds lethal to infantry and capable of damaging light vehicles.
- Armor Piercing Shot and Shell: By Kk8998982, Wikimedia Commons
- APCBC shell for a 15 inch British naval gun: By War Office, UK, Wikimedia Commons
- UBR-354P APCR Round, German Tank Museum: By Banznerfahrer, Wikimedia Commons
- APDS with tungsten carbide core: By Argonaut9999, Wikimedia Commons
- APFSDS shortly after exiting the muzzle: Wikimedia Commons