For the tread-heads: tanks explained?

[[TW]Wilsonam]

1. Ballistics

Basically, the game uses the same form of ballistics calculations for large projectiles as for small arms. This means that we are tracking the actual flight-path downrange.

2. Armor locations

[Layouts now in the media section of the website]
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.

3. Key hit locations

T-34:

http://www.heroesofstalingrad.com/wp...t34_page_2.jpg

• 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

Panzer IV:

http://www.heroesofstalingrad.com/wp...z24_page_2.jpg

• 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

4. Penetration calculation

This gets complicated!

KEY POINT: here is a thing that most people don't realize about armor penetration... it is all probabilistic at core. People rush off and hunt down "penetration tables", but you 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, we generate a Penetration:Resistance ratio and plot the results as a bell curve. We take 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 we 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.

So, about how it works... we hold/calculate a whole bunch of data on the incoming round and the plate that is hit:

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:

• Thickness
• 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
• Results:
• - 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.

5. 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...

6. Sources & References

Before all the "debates" start about what is "right" and "wrong", we'll just explain a little about some of the rationale and the sources.

First question: "Why not just use the equations given by DeMarre/Krupp/Nathan Okun/Someone else?" Because most of those people created equations (some around 140 years ago) to handle specific naval gunnery problems. There is actually only a relatively brief period of about 8-10 years when people were researching the effects of AP projectiles against RHA targets. There wasn't much research being done prior to about the mid-1930s - and after 1945 almost everything changes gear and starts to deal with APCR/HVAP projectiles, that become "long rod penetrators", and HEAT/SCW rounds impacting modern steel armors, then composites and reactives. Willi Odermatt largely owns that - and should we do a modern version, his equations will be at the top of my list!

So, given that we also need math that will cope with every single impact, varying angles, plate and round types, ogive shape and all the rest of it, we had to derive our own.

A lot of thanks go to people on our own forums, as well as on Tanknet, who's brains we have picked over the years. These include people like Paul Lakowski, Jeff Duquette and many others. It is a tortuous process, as we have to deal with all possible impacts, but keep the calcs to something manageable within a game. We think we have a decent compromise this time!

One of the key works is "World War II Ballistics: Armor and Gunnery", by Lorin Rexford Bird and Robert Livingston (private publication, long since out of print). But there are plenty of debates about flaws in that work - and pretty much any other, so you have to try and work it out for yourself a good chunk! Add in sometimes-defunct websites like Guns vs Armor and other sources of data - Jentz oft-quoted. The full list of sources used we can show separately - it is long! But some key pieces:

• AT 285/4: 6 pdr, 17 pdr APCBC and APDS Shot Versus Stored Ammunition and Fuel Tanks, Fighting Vehicles Proving Establishment, ~1944, Classified “Secret”
• Auler, H, Shape of Armor Piercing Projectiles [tr. From German], Rheinmetall-Borsig AG, Berlin, tr. March 1948 [Originally Classified “Restricted”, DoD and Contractors only]
• Bethe, H A, Attempt of a Theory of Armor Penetration, Cornell University, May 1941 [Originally Classified “Confidential”, DoD and Contractors only]
• Bird, Lorrin, ASL Armor Studies: Exceptions to the Rule, The General
• Bird, Lorrin Rexford & Livingston, Robert D, World War II Ballistics: Armor and Gunnery [Second Edition, with Errata], Overmatch Press, 2001
• German Steel Armour Piercing Projectiles and Theory of Penetration, British Intelligence Objectives Sub-Committee (BIOS), Final Report No. 1343, September 1945, Classified “Secret”
• German Tank Armour, British Intelligence Objectives Sub-Committee (BIOS), Final Report No. 653, Undated – probably late 1945, Classified “Secret”
• German Tank Armour, Final Report No. 653, Item No. 18, British Intelligence Objectives Sub-committee (BIOS), ~1946, Classified “Secret”
• Lakowski, Paul, Notes on APFSDS, Private release, ~2007
• Lakowski, Paul, Notes on effects of Hardness on penetration, Private release, ~2003
• Penetration Figures for Ammunition at Various Angles of Armour, Unknown original source, RAC Tank Museum, 1947, Classified “Secret”
• Rolled Armor, Ballistic Properties of Rolled Face Hardened Armor and Rolle Homogenous Armor of Various Hardnesses at Normal Incidence and at Various Obliquities, Watertown Arsenal Labs, Sep 1942, Classified “Restricted”
• Stockdale, Maj D, The Perforation of Armour by AP Projectiles, Armour Section, School of Tank Technology, January 1944, Classified “Secret”
• Unkovskiy, V A, Теория Стрельбы И Ее Приложение К Стрельбе Корабельной Артиллерии [The Theory of Ballistics and Appendix on Artillery Calculations], Voenizdat, 1939

7. My favorite target spots

Just for fun - where do I aim for?

If it is a front-on shot at either tank, I'll look for the ground angle to help me out. Catch either coming down a slope at you and the Pz IV's front hull roof armor is exposed, while the T-34's glacis is suddenly at a less acute angle. Alternative is lower hull plates if I can get at them. After that, the gunner's side of the mantlet on either tank, if the range is relatively close. Failing any of those, I'll be backing off!

If you get a shot at the T-34 from the side, I go low, between the second and third road-wheels, for the ammo storage in the hull floor. Pretty much the same for the Pz IV, aiming for the main fuel tank (gasoline, more likely to brew it).

[=GG= Mr Moe]

Thanks for the info Alan!

[[TW]Wilsonam]

Originally Posted by =GG= Mr Moe

Thanks for the info Alan!

Thought it might be a good time

[Mike_Nomad]

Nice effort Alan..... Thank you.

[Admiral Piett]

That was a pretty interesting read. I'm horrible at using tanks in this game so I tend to avoid them, but one day I might try to figure them out.

[Clowndoe]

Wow, fun to read despite having no practical use for me, especially since I have my own sweet spots.

[Proud_God]

Interesting read. You should patent this, TWI

Regarding this:

Originally Posted by [TW]Wilsonam

1. Ballistics[*]Plate strength (starts at 100% - may degrade with repeated hits)

I would imagine plate strength decreases alot after penetration as well, correct?

Also, just to get an idea, how much of these calculations were not present in RO1?

[Coolicus]

Does any of this go towards explaining the extreme effectiveness of the AT rifle against the T-34 turret particularly? It simply shouldn't penetrate .

[SagaciousZZzz]

Thanks for the examples, would love to see one with the AT rifles too!

[hekuball]

Originally Posted by Coolicus

Does any of this go towards explaining the extreme effectiveness of the AT rifle against the T-34 turret particularly? It simply shouldn't penetrate .

sorry, i don't know much about tanks here so humour me a little, but what would be the purpose of having an AT rifle that can't penetrate tank armour?

[Avtomat]

Originally Posted by hekuball

sorry, i don't know much about tanks here so humour me a little, but what would be the purpose of having an AT rifle that can't penetrate tank armour?

Oh it can penetrate armor allright. But not T34's armor
Unless you hit the top armor of the T34, it should be impervious in reality.

PzIV tough. Side armor at 100 meter-ish, rear at 200-ish. Top armor is like butter.

Also, APCs will be included in the game in time, thats where AT rifles will really shine.

[[TW]Wilsonam]

Originally Posted by Proud_God

I would imagine plate strength decreases alot after penetration as well, correct?

Also, just to get an idea, how much of these calculations were not present in RO1?

Yes and lots of it was not present in RO1. In RO1, we just had a "facing", not individual plates, for example. Much more simplistic.

Originally Posted by Coolicus

Does any of this go towards explaining the extreme effectiveness of the AT rifle against the T-34 turret particularly? It simply shouldn't penetrate .

Yep. And the AT Rifle should now fail against the T-34 front mantlet. You really will have to go for weak points.

Originally Posted by hekuball

sorry, i don't know much about tanks here so humour me a little, but what would be the purpose of having an AT rifle that can't penetrate tank armour?

AT rifles were designed after the first world war, in the 1920s, to combat the armor around at the time (15-30mm). They were really obsolete by 1942, but remained in service, mostly just because they existed. But they are useful against weak spots...

[Extension7]

Nice write up, so much info ._. too much to handle :P

And sweet! Glad to see you fixed the AT Rifle OP-ness :3

[Nikita]

Originally Posted by hekuball

sorry, i don't know much about tanks here so humour me a little, but what would be the purpose of having an AT rifle that can't penetrate tank armour?

Well, you might as well ask the Russians why they bothered with the charming little Model 1937 45mm AT gun they carted about from the first days of the war right up through Kursk despite its inability to knock out German medium tanks from anything but point-blank range. They used what they had, and for the most part, the Russians lacked a good infantry AT weapon right up until the end of the war. The PTRS would still do a number on a halftrack or armored car, though.

Excellent read! Diagrams confirm what I've already been aiming at, which is good, I suppose. Thanks for taking the time to put this together!

I'm afraid I'm a little unclear about how fires are modeled. As far as I know, it doesn't seem like there's any way to tell if your tank or an enemy tank is brewing up. Fantastic post, though!

Also, do tanks still spontaneously blow up every so often if you machine gun an unhatched crewman?

[The Beast (nl)]

I want to thank you for writing this for us. I hope that more players comes to the gumrak map.

[Roland Kaul]

Nice write up and thanks for the explanation. Makes sense to me, and props because you guys definitely did your homework.

[Vyllis]

Yep. And the AT Rifle should now fail against the T-34 front mantlet. You really will have to go for weak points.

Good, good !

[clambo]

This is exactly the data I was looking for - thanks

[Yoshiro]

This has now been added to the Tripwire Wiki: http://wiki.tripwireinteractive.com/index.php/RO2_Tanks

Now as a reminder, we have a wiki! Help us populate it with good material!

[Massimo92]

Damn thank for the detailed info!