The tank gun fires sub-caliber shells, and they hit very hard.
Instead of an introduction
There is a lot of talk today about the fact that Tanks They have almost completely lost their relevance as a means of combating enemy heavy armor. It is said that even during the Arab-Israeli wars, the number of head-on tank battles began to decline significantly, and during the special military operation in Ukraine, the number of such clashes became minimal.
This is partly true, of course. Leaving aside such "passive" weapons as mines, it can be stated that it is precisely shaped-charge munitions, mostly in the form of various anti-tank weapons, that missiles and grenades, also used for equipping drones, became dominant on the battlefield.
However, it's not worth discounting the tank gun's highly effective effectiveness against enemy tanks. And there's no need to engage in demagoguery with lengthy arguments designed to prove this. It's enough to remember that the ammunition for these guns includes armor-piercing discarding sabot (APFSDS) rounds—or APFSDS, as you prefer.
Overall, shells of this type don't exactly reach the top of the armor-penetration charts—missiles with HEAT warheads, especially tandem ones, often penetrate more. Nevertheless, subcaliber shells have at least two compelling advantages that HEAT munitions currently have no way to counter.
The first is a much lower sensitivity to protective structures. APFSDS, which is evolving in penetrating power, is very difficult to protect against with passive composite armor with low-density components, forcing designers to increase armor weight by increasing the thickness of steel plates, using heavy high-density alloys, or employing difficult-to-manufacture ceramics.
However, there are no mass-produced active protection systems yet that could effectively "shoot down" APFSDS shells as they approach a tank, just as there is no mass-produced dynamic protection capable of radically reducing the armor penetration of the most modern projectiles of this type.
Second, armor-piercing fin-stabilized discarding sabot (APDS) projectiles have a powerful after-armor effect. This is what we'll discuss.
It's not just armor penetration that matters
The bare figures of any projectile's penetrating power are certainly a significant parameter. After all, the 900+ millimeters of armor penetration of an anti-tank HEAT missile or the 500 mm of penetration of a drone-mounted PG-7L capable of striking a tank's vulnerable spot in themselves inspire confidence in the target's destruction.
However, in practice, relying solely on this characteristic is not enough—behind-the-armor effects must also be taken into account. Simply put, this is characterized by the degree of damage inflicted on the tank's internal equipment, including fuel ignition, combustion and detonation of its ammunition, as well as massive injuries to crew members.
In our case, the highest priority is damage to ammunition and fuel tanks, since statistically, irreparable losses of tanks and crews occur precisely due to explosions and fires.
In the case of HEAT and sub-caliber projectiles, this damage occurs due to primary and secondary fragments. Primary fragments include fragments from the sub-caliber projectile and fragments of the HEAT jet that enter the armor space behind the armor. Secondary fragments primarily include armor fragments formed during the projectile's penetration of the armor barrier.
About the aluminum equivalent
Unfortunately, there's no publicly available data on the fuel tanks and ammunition loads of foreign tanks, but there is for Soviet tanks, allowing us to estimate the "average temperature in the hospital." This data is expressed in terms of the so-called aluminum equivalent—the ability of fragments (including projectile fragments and the cumulative jet) to penetrate a given thickness of aluminum plate.
For example, fragments capable of penetrating 5 mm or more of aluminum sheeting are highly likely to ignite propellant charges in combustible cartridge cases. Moreover, the more fragments, the higher the probability.
The detonation of cumulative projectiles stored in the tank's ammunition stowage is caused by fragments with a penetration of at least 45-50 millimeters of aluminum sheet, while fragments with an armor penetration of 25-45 mm of aluminum sheet cause the ignition of explosives in the cumulative projectiles, which can potentially lead to the ignition of powder charges and the destruction of the tank.
As for high-explosive fragmentation shells, when loaded with TNT (for example), detonation occurs upon impact with fragments that penetrate more than 35 mm of aluminum sheet. Impact with fragments that penetrate 60 mm or more of aluminum sheet results in incomplete detonation of the explosive in the shell.
Fuel such as A-72 gasoline can be ignited by fragments capable of penetrating approximately 40 mm of aluminum sheet. TS-1 kerosene is slightly less sensitive, requiring fragments capable of penetrating 50 mm or more of aluminum sheet. And diesel fuel such as DL requires fragments capable of penetrating more than 60 mm of aluminum.
Numbers are numbers, but what are the facts?
When shaped-charge munitions penetrate armor, they can generate a large number of secondary fragments, potentially numbering in the hundreds. However, the vast majority of them have a penetration of no more than 5-10 millimeters of aluminum alloy. This means that even though armor penetration can create a massive fragmentation field, their after-armor effect is comparatively low.
Radiographs of copper shaped-charge jets after penetrating a steel and fiberglass barrier. Source: "Special Issues in Terminal Ballistics."
These fragments can certainly cause considerable damage to the crew and the vehicle's internal equipment. However, due to their low armor penetration, they are often unable to ignite the propellant or detonate the explosive-containing shells in the ammunition racks. Although they can sometimes ignite propellant charges, this is only possible if there are no obstacles in their path; impact with such obstacles quickly consumes their already low energy.
Essentially, the main damaging factor of HEAT munitions is the HEAT jet. Tests have shown that even fragments with low residual armor penetration are highly likely to ignite the fuel, as well as detonate and burn the ammunition. The only problem is that these fragments do not have a large dispersion angle.
An example of the behind-the-armor effect of a shaped-charge jet. A shaped-charge munition (presumably an RPG grenade) struck the side of an Abrams tank in Iraq. The shaped-charge jet penetrated the side of the vehicle, passed through the gunner's seat, and struck his body armor near the back.
The tank is subject to restoration. According to the report, the commander and gunner sustained minor shrapnel wounds: the gunner's arm, and the commander's arms and legs. The two photographs attached above show the hole from the HEAT stream and the area where it impacted the seat back.
In other words, they don't have a large area of effect, so the shaped-charge jet (exaggerated, of course) needs to hit the fuel tank or ammunition rack more or less accurately. Hence all these quite realistic storiesWhen a tank withstands multiple RPG or drone hits and manages to escape the battlefield, this doesn't mean the tank's armor wasn't penetrated—it means the HEAT jets didn't hit anything important.
With fin-stabilized armor-piercing subcaliber projectiles, things are completely different.
"Crowbars" (slang for APFSDS rounds) with a hard-alloy or heavy-alloy core, or solid-body rounds made entirely of heavy uranium- or tungsten-based alloys, produce a huge number of fragments when penetrating armor. Much, of course, depends on the armor configuration, the configuration of the APFSDS round itself, and the residual penetration, but generally speaking, the situation is as follows.
Some of them have a penetrating power of 30 millimeters or more in aluminum equivalent. Moreover, they have a wide dispersion angle, increasing the likelihood of damaging fuel tanks and ammunition even if they are not in the projectile's trajectory.
For example, during testing (), the Soviet 3BM26 Nadezhda OBPS, when hitting a steel armor barrier, will be able to generate a mixture of primary and secondary fragments in the amount of up to 200-300 pieces with a penetration of 3-6 millimeters of aluminum alloy at a dispersion angle of 120 degrees.
The number of lethal fragments with a penetration of 30 millimetres or more can reach up to 37 units with a dispersion angle of up to 32 degrees - essentially like a cloud of shot from a gun, expanding as it moves away from the point of fire.
An example of fragmentation of an APFSDS projectile made of a heavy tungsten-nickel-iron alloy with an aspect ratio of 15 (the core length is 15 times its diameter) when interacting with thin steel barriers. b/dс is the ratio of the barrier thickness to the diameter of the projectile's active part body. The top row shows radiographs of actual bodies; the bottom row shows the simulation results. Source: "Special Issues in Terminal Ballistics"
Solid-body APFSDS rounds made of heavy alloys also possess high after-armor effectiveness. According to calculations conducted back in the USSR, a relatively "weak" tungsten shell with a body length of 480 mm and a diameter of 30,8 mm produced 200-300 fragments with a penetration of 3-6 mm of aluminum at a 100-degree angle, and 7 lethal fragments at a 20-30-degree angle.
With increased residual penetration, the projectile generated 300-400 fragments with a penetrating power of 3-6 mm of aluminum and 20-25 lethal fragments with a 12-degree dispersion angle. Considering that in both cases, the projectile used was comparatively weak (only 480 mm long), it can be assumed that the after-armor effect of modern, heavy, elongated, solid-body APFSDS rounds (our Svints, the American M829 family, etc.) will be significantly higher—they have much more useful material for fragmentation.
It is precisely because fin-stabilized sub-caliber projectiles are capable of creating a massive fragmentation field, some of which have good scattering angles in terms of area of destruction and high armor penetration, that they are considered one of the most dangerous for a tank in terms of behind-the-armor effects.
A hit by this type of shell on a tank (if the armor is penetrated) almost always results in serious consequences, including shrapnel wounds to the crew, the destruction of numerous internal components, and a high risk of fires and explosions. The likelihood of a "happy ending," as with shaped-charge munitions, is very low.
Western countries are demonstrating this beautifully—they have no intention of abandoning high-impulse guns. Prospective armored vehicles regularly feature high-powered guns at exhibitions and demo videos, ranging from 130mm smoothbore guns to the promising Ascalon 140mm APFSDS-equipped antitank guns, which are more than half the length of an average man.
After all, a tank must be able to fight its own kind. And sub-caliber rounds are one of the most effective anti-tank weapons in its arsenal.
Information sources:
"Special Issues of Terminal Ballistics." Bauman Moscow State Technical University. V.A. Grigoryan, A.N. Beloborodko, N.S. Dorokhov, et al.
"Tank Theory and Design." Volume 10, Book 2. 1990.
"Behind-the-Armor Action of Armor-Piercing Sub-Caliber Projectiles with Heavy Alloy Cases." V.M. Bakshinov, S.V. Lomov, V.I. Timokhin
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