IS-2 in Soviet Campaign *** Spoiler ***

[JasonC]

As for the IS-2, multiple points. First, the basic hull armor and confusion over 100 vs 120 thickness is all due to the switch in the "not early" model, which dispensed with the 120mm thick but low slope top of the front hull, superstructure section, in favor of a uniform 100mm glacis fully sloped at 60 degrees. This is covered by Wikipedia with full diagrams and really shouldn't be any mystery. That also shows that the front turret not covered by the mantlet, but around it, is 100mm thick as well as round for angle.

Any pretence that they were aiming at 100mm protection for the whole front is thus toast at the outset. They accepted 100mm plus 30 degrees only for the lower hull, they accepted 100mm plus round for angle only for the turret edges. For the glacis they wanted 100mm thick *plus* full 60 degree slope, which more than doubles the effective thickness. They had found 120mm plus 20-30 degree slope inadequate on the early models. So clearly they were accepting 100mm only with slope and only on smaller parts of the front.

As for the sources for the 160mm figure for the max of the mantlet over turret front, it is given in (1) Zaloga, (2) by Denizen on the CMBB forums back when we had this conversation for CMBB, and (3) the tank diagram textbooks the latter cited then (you can track them down, this was ten years ago but they were definitive IMO).

How does it come about, physically? You have a 75mm mantlet plate lying on top of a 90mm turret face, but with some taper of the mantlet plate itself. The max physical thickness is 160mm. I have seen sources that rate the joint resistance as low as 130mm single plate. But it is certainly well above 100m flat. The turret front is *not* the weakest part of the tank.

I note also that in early CMBB modeling, German layered plates were consistently modeled as resisting more than single piece, which I among others argued was completely wrong, but helped give us the uber StuG. The same folks tried to give us JS-2s with flat 100mm front armor resistance, to the point where Panzer IVs were outscoring them in straight up fights at 800 to 1200 meters. This was too laughable a piece of German physics to survive the next few patches. The early IS-2s were left nerfed but the later ones became real heavy tanks, with little fanfare or admission that the German physics lobby had screwed the pooch.

But Denizen had it right from the get go, because he had excellent sources and no axes to grind. Unlike some others that BTS relied on at the time, rather too heavily.

[Vanir Ausf B]

This is an early (narrow mantlet) IS-2 captured by the Germans with the measured armor thicknesses conveniently stenciled on the tank.

[Amizaur]

Amizaur re 1000 meters, um, I don't think that is so easy, unless the tank is moving fast throwing up dust, or firing with a nice big muzzle blast while you were watching, or similar.

http://www.chuckhawks.com/f-class_1000_yards.jpg

Yes you're right, I had a moving target in mind, sorry I didn't mention that.

[Amizaur]

Any pretence that they were aiming at 100mm protection for the whole front is thus toast at the outset. T

I said that the TURRET armor seems to be designed with 100-120mm protection level in mind (so definitely NOT 160mm). It's hard for me to guess if they wanted 100 or 120mm but the front turret/mantlet armor is about that thick in near-vertical areas. Max 120mm (mantlet in vertical part), min 100mm (front turret and slighly-sloped parts of mantlet).

I'm not discussing hull armor here.

I don't trust written sources if they contradict each other. I take a ruler and go to measure myself, if I can. I did and I'm sure there is no 160mm parts of mantlet armor other than sum of mantlet + front turret in places where they overlapp.

The physical thickness may reach 160mm in some places. If those sources say simply than "the front turret thickness is 160mm" then it's a poor source, whatever the author is. If they say "up to 160mm" then it could be true.

The idea of 160mm max thickness could also come from some cross-section that can be found at IS-1 manual (and possibly IS-2 manual). The solid area around the barrel opening is drawn in a way that it can be interpreted as if the mantlet was so thick, but it's just reinforced part that the cross-section was cut trough...

The most vunerable parts of front turret would be front turret armor on the left and right of the narrow mantl, or right of the wide one - vertical parts of 90-100mm thickness. And of course any hit on sight/MG opening or hit at the gap between mantlet and turret armor. The mantlet/turret armor castings seem to be very crude and hard. It's probably not very resistant if overmatched, so 70mm + 80mm of this armor would not resist well (the overlaping part).

One more thing - the casting is SO crude, that I absolutely believe in +/- few centimeters difference in armor thickness between two turrets, and the armor quality just can't be good looking at it's surface.

Link to more pictures full resolution (RAR archive, about 120MB): https://dl.dropboxusercontent.com/u/72669076/IS-2%20photos%20by%20Amizaur.rar