AP, APCR, APCBC, PzGr39K, HEAT... you see these terms referred to during the game. But have you ever wondered what all these abbreviation means and what they refer to?
If you have not done so already, I can only recommend you watch our video explaining the “mechanics of penetration”.
It is worth mentioning that this topic is wide enough to fill a series of books, so for this article, we will mainly focus on the anti-tank rounds used during our game's period. Ballistic and propelling charges will not be covered, but if the matter interests you, you are welcome to voice it by commenting on this article on our forums and we will dedicate a full article about it.
First, a lesson on vocabulary from the US Army Field Artillery School and various sources:
An explosive is a gaseous or solid substance that, when affected by a sudden increase in pressure and/or temperature, undergoes a violent chemical reaction (decomposition). This results in the simultaneous release of great quantities of light, heat, and gas. The rate of decomposition of a mass or column of explosive under controlled conditions (in measurable feet or metres per second) determines whether the substance is classified as a high explosive or a low explosive.
Measured in feet or metres per second, velocity is the rate of decomposition of a solid substance. The rate of decomposition of a substance is controlled by the ingredients of the substance; by the design, size, and shape of the substance (powder grain); and by the chamber of the weapon for which a particular powder grain is designed. When the substance is a low explosive (i.e., propelling charges), the decomposition rate is called the deflagration velocity. When the substance is a high explosive (i.e., bursting charges), the decomposition rate is called detonating velocity.
The process by which the outer layer of a substance burns and transmits the burning effect to the inner layers of the substance is called deflagration.
Detonation is the violent, noisy decomposition of a high explosive, such as that of a high-explosive projectile.
Power is the ability of an explosive to displace or move its surrounding medium.
As opposed to power, brisance is the ability of an explosive to shatter its surrounding medium.
A shell is a payload-carrying projectile which, as opposed to shot, contains an explosive or other filling. However, modern usage of the term sometimes includes large solid projectiles which should really be called shot (AP, APCR, APCNR, APDS, APFSDS and proof shot).
Very similar to a shell (see above), a shot is a pure kinetic projectile that does not contain any filling or explosive. Solid shot may contain a pyrotechnic compound if a tracer or spotting charge is used.
The most common shell type is high explosive, commonly referred as HE. They have a strong steel case, a bursting charge, and a fuse.
Upon impact the fuse detonates the bursting charge, which shatters the case and scatters hot, sharp case pieces (fragments, splinters) at high velocity. Most of the damage to soft targets such as unprotected personnel is caused by shell pieces rather than by the blast.
In near hits, fragmentation from high explosive shells HE with point-detonating (PD) fuses penetrated this armoured vehicle, destroying critical components and injuring the crew. (source: Field Artillery November-December 2002)
Armour Piercing, or solid shot, it is usually a pure kinetic projectile that does not contain any filling or explosive. Such shots designed for armour penetration were solid metal.
They almost always had a specially hardened and blunt shaped nose to facilitate penetration. Consequently, its shape was far from perfect on the ballistic side and accuracy was lowered compared to other, more profiled shells, like HE.
The bluntness of the AP shot is designed to produce a rapid increase in shot to armour contact area as the shot slows down upon impact. If the shot was streamlined and more profiled like a HE, the impact would quickly shatter the AP and render it useless.
Theoretically, a flat-nosed shot would provide the best performances, but this shape has other drawbacks and would not be used as it is.
This was the main anti-tank ammunition of the British, and was also used on and off by many nations, with the exception of the Germans and Russians, who always used APHE respectively for shells above 20mm and 37mm.
AP of over 50mm were also often equipped with a small bursting charge and delayed action fuse instead, adding extra lethality once the shell has finished ricocheting and destroying internal modules. Only a tiny amount of explosive is necessary as the explosion occurs inside the tank, a very confined area, producing many extra ricocheting fragments, and is often enough to kill, ignite fuel vapours, or explode ammunition.
|1- Shell 2- Bursting Charge 3- Fuse and Tracer 4- propelling charge||British 6 pounder full round|
It worked well in theory, but had a few practical drawbacks; first, the explosive charge could reduce the weight of the shell to half of a conventional AP shot. Lighter shells have greater initial velocity, but less momentum, lose more speed over distance, and therefore have reduced accuracy and penetration the longer it travels.
The second issue was the fuse itself. It was a very difficult technical problem to make sure it detonates at the right time. There are many cases of fuses which never went off, or actually went off too late, after the APHE pierced through the target.
To compensate for this issue, an attempt was made to increase cannon length and to harden projectiles, improving muzzle velocity. This went well until physics started to kick in, with impact stress causing the shot to shatter upon impact. This can be observed in-game on the VK 3601 (H) with the 7.5 cm KwK 41 L/58 Konisch Cannon. Normal AP shells have reduced damage, while APCR have a normal effect. We will talk about the latter in a moment.
A new solution was therefore developed – APC
To allow an increase in impact velocity without shattering the shell, these were initially fitted with soft steel penetrating caps. The impact stress was transferred away from the tip of the round, and the cap squished upon impact added an extra effect to prevent tracking against sloped armour, reducing the chances of ricochets. However, capping reduces ballistic properties and results in a lower impact force focused on the armour.
(British Royal Ordnance 9.2 inch shell)
Another improvement to the standard AP rounds, the Ballistic Cap was designed to improve the ballistic property of the AP round by giving it a more aerodynamic shape like HE shells, without affecting its penetration ability.
This would increase the speed and accuracy of the round.
Of course, after reading about the Piercing Cap and the Ballistic Cap, we all knew this was to come. Combining the ballistic property of a profiled shot, shattering protection for high-speed impacts and greater "grip" against sloped armour, shots combining both were quickly designed.
|Tiger I full round with ballistic cap, piercing cap, shell, bursting charge, fuse, tracer, and propellant charge.||BL 15 inch Mark I shell (British Naval gun)|
Previously, we talked about capped and ballistic capped shells. The first one was to prevent the shell from shattering upon impact and helped prevent tracking (bouncing off). The second was to improve the ballistic properties of the shell, increasing muzzle speed and accuracy. It was effective against carburised steel armour, until the appearance of homogenous heat-treated armour, when impact strengths rose to a new level at which even APCBC had limited effects. No suitable solutions were found, and as the impact velocity started to rise above 900m/s, even APCBC started to shatter. The increased use of heat-treated low alloy steel marked the end of the conventional AP shell.
Eventually, a new solution was found, in the shape of a new material with extremely high hardness for penetration, enough stress resistance to withstand impact without shattering (improvable by capping), and very high weights for momentum. The material was Tungsten Carbide. Of course, this wasn't without drawbacks –its extreme hardness required specialist manufacture, and its large weight ruled out the option to make a solid shot. Solid shots of Tungsten Carbide would only reach 60 to 85% muzzle velocity of a comparable AP shot, greatly reducing speed, range and accuracy. Also, Tungsten Carbide is relatively expensive.
The solution came in the shape of a shell carrying a small Tungsten Carbide core inside, which was released upon impact. The reduced size and weight of the core while keeping the same size and propellant charge allowed for a much greater initial muzzle velocity and impact speed.
The British will call it Armour-Piercing Composite Rigid (APCR) based on the material used, the US will designate it as High Velocity Armour Piercing (HVAP) from its increased speed, and the Germans call it Hartkernmunition (Hard Core Ammunition).
This concept will lead to APDS (Armour Piercing Discarding Sabot) where the whole shell is discarded after being fired, leaving only a spin-stabilised core rushing at high speed towards an unlucky target.
This would be even further improved with smooth bore cannons and fin-stabilisation, leading to APFSDS rounds, but we won’t go into that as it goes beyond the scope of World of Tanks.
High explosive anti-tank rounds are shaped charges designed to orientate an explosion towards the armour, creating an extremely high pressure capable of stabbing through the target point.
Contrary to popular belief, HEAT rarely reaches above 600°C and is incapable of melting treated steels, which can easily withstand temperatures of 1400°C. It is the sheer pressure from the explosion that pushes through the armour, projecting inside the tank a blast of copper fragments from the liner that was holding the charge together.
It was first used for Grenades, PIAT (Projector, Infantry, Anti-Tank) and bazookas. Adapting it to tanks was somewhat more difficult as the spin stabilising the round would spread the explosion and greatly reduce efficiency.
Germans used a driving band on bearings to allow it to fly unspun from their existing tank guns, while many nations limited themselves to recycling obsolete low-velocity howitzer as the impact velocity did not influence the round's efficiency.
picture by Aleksej fon Grozni
A spall is a flake of material usually created by corrosion, weathering or projectile impact. I'll let you guess which one interests us the most...
High Explosive Squash Head (HESH) or High Explosive Plastic (HEP) were designed by the British to serve as the main HE shells for attacking concrete fortifications during the Cold War.
The thin metal head is filled with a plastic explosive, and a delayed-action fuse at the base of the shell. The fuse detonates the plastic explosive right after impact when the explosive is squashed against the armour, resulting in a massive shockwave.
It was surprisingly effective against armour, ripping off elements near the impact point and generating numerous spalls bouncing inside the tank, causing lethal damage to the target without penetrating it.
Since the appearance of layered composites armours in the 1970's, HESH has gradually fallen out of favour as the shockwave does not spread efficiently through the multiple layers of armour. However, it is still used today against fortifications, soft skinned vehicles or ground troops.