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25 December 2013

Developers' Diaries: Ground Forces Damage Model [Part 2]

In the previous issue of the Tank Diaries we explained the basics of Damage Model for Ground Forces. Today we will tell you about the ammunition in War Thunder Ground Forces.




To make things more clear we will show how tank is damaged. We use special damage adjustment system.


Let us hit T-34 with a 75 mm KwK40 using cavity AP shell with PzGr39 balistic and protective cap from a short distance.


White line is shell’s motion vector (bottom left corner), yellow dot - a place where shell hit the armor, light blue lines - cone of armour shards. Tail fuse of the shell went off and the shel detonated  approximately in the center of  the fighting compartment. Yellow circle is HE damage radius, green sphere is fragmentation damage radius. Red traces from the center of the explosion - fragments that hit vital modules.


 

Also screenshot shows silhouettes  of the significantly damaged modules - breech part of the gun and crew members(red boxes), turret ring engine and ammo rack - green boxes . Crew members were critically hit and are knocked out. Tank combat efficiency is significantly reduced but it is not yet destroyed since one of the crew members is still alive. Now let’s make a second shot.


 

Second shell also hit the front armour, penetrated it and exploded inside - tank is destroyed.


 



Ammunition


All existing ammunition is divided into following groups::

  • Armour-piercing kinetic-energy  (including subcaliber) 

  • High-explosive anti-tank

  • High-explosive fragmentation

 

Detachable equipment of  PzKpfw IV Ausf.F2

Armour-piercing shells


 All kinetic-energy armour piercing shells work on the same principle and the only difference is whether they have explosive or not (cavity shells - APHE/APHEBC/APCBC )  and their penetration value.  All shells have similar pointed AP projectile construction.  

In game it works the following way - each shell has charateristics that affect its trajectory (mass, initial speed,  ballistic coefficient)  and its killability (armour penetration scheme depending on distance, kinetic damage scheme depending on distance, separate characteristcs of exposive’s killability ). When the target is hit several calculations are made :

 
  • breach check - if caliber is everal times higher (10) than plate thickness it breaches the plate automatically. 

  • if there is nobreach - bound check. Bound shot is possible if the angle is 30 degrees or less. The less the angle the higher is the chance of the bound. 0 degrees angle means 100% bound shot. 

  • If there is no bound shot - then goes penetration check, following characteristics are taken into account - current penetration value, armour slope angle, and slope angle of the machine itself, angle of impact. Armour thickness is calculated and there goes a check whether a shell can or can not penetrate the armour.If not and the shell has explosives - it detonates and  attachments can be damaged. 

  • If there is penetration the shell deals the damage to the armor, loses penetration value and kinetic damage proportionally to armor thickness and goes further. Also each kinetic shell creates a shard cone that can damage modules and crew in the sector. 

(for 76mm shell height of the cone is 2.5 m angle is 15 degrees, shard damage is enough to knock out a crew member on a single hit or partially damage internal modules).
 
The shell itself goes further and when hitting any internal module all above mentioned checks are made.  Checks are made until penetration value of a shell is enough to penetrate a module or until the  fuse goes off (if shell has explosives and armor was not thick enough to make it go off) A distance needed for the fuse is 0.5-1.5 m from the penetration point depending on caliber and type.
 
When fuse goes off the explosion follows which creates HE and fragmentary spheres of damage.  Crew members and modules within the spheres may be damaged by shards and impact wave. 

 

 Stug III Ausf.F shooting PzGr 39  shell

An important thing for players to know is that even a shell without explosives damage modules not like “laser beam” on its trajectory but also in some radius. Thus if AP shell hits a spot between a driver and radio operator secondary shards will most likely damage both crew members while the shell itself if it has enough penetration value may even reach the engine..


 

High-explosive anti-tank shells 

 

These are fundamentally different from the armor-piercing shells. You can find out how the real ones work here. In game this kind of shells is simulated quite accurately: their armour penetration ability does not decrease with distance. Once the missile hits an obstacle an explosion is generated; its parameters are comparable to a fragmentation explosive shell of the same caliber allowing it to penetrate thin armour and damage the crew.

 
There is also a coherent jet formed at the point where the shell hit the target. Its effects are similar to those of a solid armor-piercing shell, striking all the modules on its trajectory and gradually losing some of its penetration ability with every module hit. The jet length is limited to a certain distance (usually 2 to 4 meters). Beyond this limit it is unable to deal any damage and dissipates quickly. Also the coherent jet generates a splinter cone with every impact, but it is much smaller compared to the conventional armor-piercing shells.
 

Fragmentation shells

 

This kind of ammunition is very similar to the aircraft carried bombs and rockets as well as automatic cannons’ HEF (high-explosive fragmentation) shells that are already present in the game. They generate spheres of explosive and splinter damage; if the numerical values of the blast wave strength are high enough, it penetrates the armour and deals damage. Medium and low caliber shells of this kind may destroy light vehicles with bullet-proof armour (like the Flakpanzer I anti-aircraft SPG). Higher caliber HEF shells (122mm upwards) are needed to destroy heavy and medium tanks.




Thus it is dramatically important to choose ammunition type according to its armour penetrating and explosive properties. Knowing  and using advantages of different shell types against different opponents may turn the tide of battle.Thus it is dramatically important to choose ammunition type according to its armour penetrating and explosive properties. Knowing  and using advantages of different shell types against different opponents may turn the tide of battle.

 

We gave you a basic description of  one of the most important game systems - the damage model.  Join discussions on the Official Forum and feel free to ask your qustions and share your ideas.

War Thunder developers team

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