The game uses the same form of ballistics calculations for large projectiles as for small arms. This means the game is tracking the actual flight-path downrange.
T-34 consists of 21 plates, plus the driver hatch and gun mantlet. The mantlet and turret are cast steel, while the rest is RHA (rolled homogenous armor). The Soviets tended to use very high hardness steel, which is a good thing against lighter rounds, but lacks ductility and actually makes it more vulnerable against heavier rounds (such as the Panzer IV's 75mm). In addition, there are the turret vision slits as potential targets.
Panzer IV is a more complex shape, totaling 45 plates. The Germans used mostly RHA, with some of the key plates in the 30-50mm range being faced hardened (FHA) to a depth of about 5mm. The intention with FHA was to provide a harder outer face, to defeat smaller projectiles, while the remainder of the plate provided more ductility to defeat larger rounds. Also modeled are areas like the vision slits, with the armored glass behind them.
In game, each plate is modeled in its correct place and angle. Using the ballistics calcs, we can work out the actual velocity and angle the projectile hits the plate at.
Key hit locations
- Crew - Gunner/Commander, Loader, Driver, Hull gunner
- Ammo - MG ammo in the back of the turret and beside the hull gunner, while the main gun rounds are stored in the hull floor, with a small number of rounds in clamps on the hull side
- Fuel - tanks are in the hull sides; diesel fuel, so less prone to fires
- Engine & transmission - the T-34 has the transmission/gearbox at the rear, as the drive sprocket is at the back of the tank
- Gunnery & optics
- Crew - Commander, Gunner, Loader, Driver, Hull gunner
- Ammo - MG ammo beside the hull gunner and in the hull behind the loader, main gun rounds stored in multiple bins around the hull, with the largest right behind the driver
- Fuel - tank is in the hull floor; gasoline
- Engine & transmission - rear engine, drive shaft down the center of the hull floor, with the transmission front and center, gearing front sides
- Gunnery & optics
A thing that most people don't realize about armor penetration is that it is all probabilistic at the core. People rush off and hunt down "penetration tables", but they need to go back to the actual data measurements to understand what is going on. For instance, the Germans look for the "limit velocity" at which 3 out of 5 (or 5 out of 7, depending on caliber) rounds penetrate a test plate. They then took that number and created all those nice penetration tables from them, not the other way around! They do that to give their gunners a ready-reference guide, but it is NOT absolute.
For simplicity, Tripwire generates a Penetration:Resistance ratio and plot the results as a bell curve. Anything below a certain point as an "undermatch", which will never penetrate and any result above a certain point as an "overmatch" which will always penetrate. Anything in between will generate a PROBABILTY that the round will penetrate - and compare to a random number for those cases. Probability theory at work. It is NOT absolute - even in German testing, they were looking for the point where the "majority" of rounds penetrate.
For the round/projectile:
- Muzzle velocity
- Hardness (BHN)
- Caliber (actually "d", the size of the projectile - SUB-caliber projectile for APCR/HVAP)
- Max RHA (take from the ever-friendly bollox tables on the internet)
- Actual RHA (This one is tricky: it is basically the theoretical 50% probability thickness penetrated at point-blank)
- Test plate hardness (BHN) (i.e. what was this round normally tested against?)
- Slope effect modifier - largely dependent on the ogive shape/effect
- Shatter number & Shatter T/d - dictates when a round is likely to shatter
- Shatter penetration effectiveness - the effect that shattering has on penetration capability [a round that shatters is perfectly capable of penetrating - and the effects are messy]
For the armor plate:
- Angle to vertical
- Type (FHA, RHA, Cast)
- Face hardness
- Depth hardness
- Calculate overall hardness on 5mm of Face hardness, remainder at Depth hardness
- Flaw multiplier (100% for "perfect", 90% for badly flawed armor)
- High hardness plate (Y/N) (Usually "Y" for thin plate)
- Plate strength (starts at 100% - may degrade with repeated hits)
And the calculations:
- Calc T/d (Thickness of plate/diameter of projectile)
- Resistance calculation for the plate: allows for high hardness plate effects, the difference between the target plate and the normal test plate and the angle of incidence with the armor (including the slope coefficient)
- Possible projectile shatter - if T/d > the round's Shatter T/d, the round may shatter
- Penetration calculation for the round: modify the Actual RHA figure for the impact velocity of the round
- Pen:Res is Penetration:Resistance ratio
- Final projectile shatter is dependent on Pen:Res, accounting for the impact velocity; if the round shatters, the Penetration is adjusted, also Pen:Res
- If the final Pen:Res < 0.89, then the round is under-matched and will FAIL to penetrate
- If the final Pen:Res > 1.12, then the round over-matches the plate and penetrates intact
- For anything in between, we generate a random number for comparison. If Pen:Res = 1.0, for example, there is a 50% chance the round will penetrate (see where "Actual RHA" comes from now?)
- If the round remains intact, but fails to penetrate, it has a chance of generating spalling
- Deflection: if the round stays intact, but fails to penetrate, we degrade the velocity and track its progress, just in case it manages to hit a weak spot!
A couple of worked examples:
T-34 round impacting Panzer IV upper front hull plate (beside the driver's front view slit) at 300 meters: The round is a 76mm round, impacting at 603m/s, actual angle of impact 33 degrees (plate is at 5 degrees off the vertical, flat ground, tank angled at about 30 degrees). The plate is 50mm FHA, overall hardness BHN 357.
- T/d = 0.66
- Final resistance of the plate is 63.6mm - slight increase for the plate being harder than Russian test plate (BHN 300), plus the effects of the angle, against the Soviet BR-253A projectile
- Penetration for the round is now 78.9mm, but the impact means that the round DOES shatter
- Final penetration capability of the projectile, allowing for the shatter is 63.1mm, giving a final Pen:Res ratio of 0.9919
- No overmatch or undermatch - and the bell curve gives us a 46.9% chance of penetration
- On this occasion, random number generator says it fails to penetrate: the round deflects at 97 m/s - which doesn't matter anyway, as the round has shattered
Panzer IV impacting T-34, left side, between road-wheels 2 and 3, actual angle of impact 43 degrees (plate is vertical, tank moving at an angle across the Panzer's front). The plate is 45mm RHA, hardness BHN 400 - high hardness plate.
- T/d = 0.60
- Final plate resistance is 60.7mm - it would be higher if it wasn't high hardness plate
- Penetration for the round is 104mm in this case and it doesn't shatter, leaving the penetration unchanged, giving a Pen:Res ratio of 1.7187
- This is an immediate Overmatch - that side plate is no match for the incoming 75mm round, even when angled and at 500m range
- The round penetrates - clipping through the forward left fuel tank and into the main ammo storage in the hull. Scratch one T-34.
Behind armor effects
Any projectile that penetrates intact is tracked to see what it hits inside the tank, through the key hit locations. If a round shatters as it penetrates, then it will enter the tank as shrapnel. A round that almost penetrates may also spall pieces of steel off the inside face of the armor, which is also treated as shrapnel. Interior components can all be damaged or destroyed (depending on server settings). A level of "general damage" is also applied, which goes towards a general starting of fires - and usually guarantees that a tank can't take more than 3 or 4 penetrating hits without blowing up. Assuming that an earlier penetrating hit hasn't lit up the fuel or engine, or set off an explosion in the ammo stores