2 hours ago, AraMacao said:
IS-7 is praised for it's armor and big gun with seemingly no downsides. Maus is infamous for the obvious downsides that came with it's thick armor and big gun. Huge size. Very slow. So heavy it would break bridges and even crush roads. IS-7 had better armor than maus, a bigger gun with autoloader, much smaller size and way faster movement. Everything better. How could this be? What secrets did the russian engineers have?
Better design.
The IS-7 used primarily a cast turret, which can be cast into complex shapes, reducing the wasted volume of a tank:
Here you have 3 armor shapes around a turret ring. Shape number one resembles the Maus turret, and as you can see, it is terribly inefficient. Shape two is akin to mid to late war tanks, like the T-34 or Panther. This shape cuts away the corners, being more volume efficient. However, compared to the cast circle around design 3, it is still very inefficient. The round shape of the cast design also gives more sloping, increasing the frontal armor noticeably. This, and cast armors ability to freely chose thickness, allows the armor to become thinner and thinner towards the rear, effectively allowing it to provide the same protection arch, at a lower weight.
Here you can see it quite pronounced, albeit in a more modern design. Compare this to the Maus, which has 220mm all the way to the back, and you can see some mayor weight savings. This can also be done in a different axis:
Here you can see the armor getting gradually thinner and thinner as the sloping increases, eventually taking a sharp drop in thickness when the angles passes the ricochetangle of common shells.
All of this is very hard to accomplish with welded armor.
The hull on the IS-7 is also noticeably different. It features a pike in the front, effectively angling it it two axis, increasing the effective armor without increasing the weight. It is also more heavily sloped overall, compared to the Maus. The Pike greatly increases frontal armor, at the cost of being unable to angle the tank for better protection, but at a engineering standpoint, the pike provides more efficient use of space, cutting away the useless space at the sides of the driver, further reducing the internal volume of the tank. Here, both tanks use welded hulls, since the angles do not require complex shapes, and RHA is generally more weight efficient compared plate to plate. Notice the heavily sloped sides compared to the Maus.
The IS-7 came in different hull designs, but both feature a V shape, which angles the side armor downwards, increasing the effective armor and further reducing internal volume and allowinga bigger turret ring that the width of the hull. Two side effects of this shape gives the IS-7 even more effective armor. First, since shells drop downwards, the effective sloping of the plate increases with range. Second, the V shape provides protection against blast mines, reducing the required belly thickness to protect against mines. This can be seen in modern vehicles like the Merkava 4, MRAP and Stryker.
When looking at the rear of both vehicles you will notice that the IS-7 is sloped backwards, and inwards. This allows for thinner plates and reduces the roof area needed to be armored. The sides sloping inwards also reduces the needed thickness, since they are no longer inside the frontal arch.
With a much more efficient armor layout, the IS-7 can afford a much lighter drivetrain and suspension. Though, instead of saving weight on the engine, they kept it at the same level as the Maus, giving it much better mobility and hp/ton. Just comparing the estimated weight of the suspension and tracks should give you a idea of how much weight more efficient armor layout saves:
In general, the suspension makes up 10% of a tanks total weight, same for the tracks. The suspension can be heavier/lighter based on the type, but still lies within 5%+-. So the Maus's suspension and tracks would weigh 18,8 ton each, in a total of 37,6 ton, already heavier than a T-34! For the IS-7 the weight would be 6,8 ton each, in total 13,6 ton. This means the IS-7 saved 24 ton on just the suspension and tracks. Other major weight savings would be in the transmission, since the Maus uses a gas-electric system, which at the time was considerably heavier than conventional transmissions. Add this on top of the Soviet's tendency to sacrifice drivetrain reliability and quality for power density and weight savings, we can see a big weight saving here.
Then of course the Soviet's in general made lighter and simpler guns than the Germans, at the cost of in general weaker guns. And with lower ammunition capacity makes for a much lighter tank. Also the fact that the Maus has a secondary 75mm cannon does not help. Also, sacrificing gun depression saves a ton of weight.
Combined with Soviet's tendency to make smaller cramped tanks, with a crew on average lower than other Europeans, and keeping the dimensions to a minimum, makes for a much lighter tank.
It's very obvious when you think about it. The reason the IS-7 did not actually get into service is because it was too heavy, as stated above. A special rail cart had to be used just for it, and it was too heavy for most Soviet infrastructure. Combined with the fact that the war ended, with no real competition in the area of heavy tanks from the allies, and the much cheaper T-54, which already was resistant over the front to almost anything the German and allies had, it was again, obvious why the IS-7 was not adopted. The T-10M is a product of this, weight savings to stay inside the restrictions, but still eventually faced out in favor or medium tanks.
Edited by xoonZG
