In War Thunder, we try to add as much details as possible to various types of combat vehicles. Spall liner is a new armored vehicle protection feature that we introduced in the Air Superiority update, which we know is widely discussed on all platforms. Wed like to explain in detail how this mechanic works, and what its capabilities and limitations are. In the near future, well be making an additional post addressing your concerns with spall liners for MBTs in general. First up, lets take a look at what spall liner is in reality. Spall liner is part of the structural protection of an armored combat vehicle, designed to reduce the damaging effect in the main compartment once a tank is penetrated. To do this, liners are attached inside of the main compartment. Material such as fabrics made from aramid fiber are most often used, but other materials are also used occasionally too. These liners help to stop part of the fragmentation flow, reducing the cone of fragment dispersion and therefore reducing the damaging effect caused by armor penetration. In the game, the effect of a spall liner is implemented as follows: inside the main fighting compartment, directly after the main portion of a tanks armor, a module is present that imitates spall liner material. These modules have the same size and shape depending on the vehicle and how it is laid out in a vehicle in real life. Taking into account the thickness and resistance coefficient, the current spall liner has a protective equivalent of 2 mm of rolled armor alongside the normal armor amount.
This module also has a structural strength parameter, which is noticeably less strength than the energy caused by a HEAT or APFSDS projectile fired from a tank. Therefore, once penetrated and hit by a powerful projectile, the spall liner is then destroyed. Secondary fragments from penetration of armor by a HEAT or APFSDS projectile have armor penetration in the range equivalent to 3 to 30 mm of rolled homogeneous armor. This wide spread in variation is due to the simulation of fragments of different sizes and energies formed when armor is penetrated. In the game, a fragmentation stream consists of several groups of fragments with different angles of expansion, having different armor penetration and damage. The more powerful the fragments, the narrower the cone of their dispersion and the smaller their number is. It may seem that theres an inconsistency here, where the 2 mm of spall liner should not have any effect on the fragmentation flow at all. But if we take into account the fact that when breaking through armor, each fragment also takes into account the angle of contact with the armor, then everything is consistent.
Fragments following a small angle of deviation from a projectiles trajectory enter the spall liner with a small angle of impact, and the equivalent protection is not enough to stop them. These fragments travel further into the fighting compartment and can damage tank modules and crew. Fragments flying with a large deviation hit the lining at a large angle, so that even a 2 mm equivalent is enough to stop them. Of course, the greater the penetration of a fragment, the fewer such fragments can be stopped by the spall liner, and the amount of fragment spread will be minimally reduced and vice versa. The weaker the fragment, the greater the effect the spall liner has. The parameters that we set up are made in such a way to slightly reduce the armor effect of powerful APFSDS projectiles and more noticeably affect the damaging effect of HEAT ammo, which coincides with information about real tests of this protection.
Wed like to also clarify that other than adding spall liners, we did not change the damage model settings. The parameters of the fragmentation field (number, range and penetration of fragments) has remained the same as before the update. However, weve noticed your feedback about the reduction of fragments after penetration. After checking, we found an error that was discovered in the game code that appeared during the process of refactoring game logic, leading to a decrease in the number of secondary fragments for some weapons. This issue has been found and fixed, and at the moment, the algorithms for fragments after penetration are working as intended. Wed like to thank you for your feedback surrounding the spall liner and issues with fragment penetration.