"Front of the hull
The design of the front of the IS-3 hull provides superior shell resistance compared to the mass produced IS-2 hull, excluding the front sloped roof of the hull. The upper front plate protects the crew from German 88 mm shells at a distance of 100 meters or more from any angle. The upper front plate of the IS-2 (Uralmash) cannot be penetrated from a distance of only 600 meters.
Photo #4. Upper front plate hit by an 88 mm armour piercing shell.
The upper front plate of the IS-3 hull can be penetrated by 122 mm sharp-tipped shells from 900 meters or more at 40 degree and 320 degree angles. At 0 degree angles, the 122 mm blunt-tipped armour piercing shell does not penetrate the front plate from more than 200 meters.
The upper front plate of the 701 tank is impenetrable by 122 mm sharp-tipped armour piercing shells from any angle.
Photo#5. Front portion of the roof hit by 122 mm armour piercing shells at an angle of 320 degrees.
Photo #6. Upper front plate hit by 122 mm armour piercing shells at an angle of 0 degrees.
The lower front plate of the IS-3 can be penetrated by the German 88 mm gun at 300 meters at 0 degrees, and cannot be penetrated at a distance of 1700 meters. The analogous hull section on the IS-2 hull (Uralmash) protects from penetration at a distance of 5100 meters. The lower front plate of the Object 701 cannot be penetrated by shells of this caliber at 100 meters.
Photo #7. Lower front plate hit by German 88 mm armour piercing shells at 0 degrees.
The sloped overtrack hull cannot be penetrated by German 88 mm armour piercing shells at a distance of 200 meters. The sloped overtrack hull cannot be penetrated by 122 mm sharp-tipped armour piercing shells from 900 meters.
The sides and rear of the IS-3 are identical in thickness and design to the IS-2, and exhibit the same properties as the IS-2.
Data on the resistance of hulls to shells is provided in tables ## 8, 9, and 10."
The tables provide some more data on two IS-3 hulls. The Uralmash hull cannot be reliably penetrated in the side from any distance by the German 88L/71. The Soviet 122 mm gun achieves reliable penetration at 700 meters. The lower side hull can be reliably penetrated at 1300 meters. The upper front plate cannot be penetrated by the 88L/71 at any distance, at any angle. The D-25 can achieve this at 900 meters, as shown above. The lower front plate can be reliably penetrated by the German 88L/71 at 300 meters, and unreliably at 1700 meters. A German 75 mm gun is also tested against this hull, but can only unreliably penetrate the lower side hull at 500 meters, at a 45 degree angle.
The factory #200 hull exhibits similar properties. It cannot be reliably penetrated by any German guns in the upper side, but the D-25 can penetrate it at 600 meters. The lower side hull does not do as well, the aforementioned 75 mm gun penetrates it at 960 meters at the same conditions, and the 88 mm gun can penetrate it from 1900 meters. No guns can penetrate the upper front plate, at any distance or tested angle.
A hull from the Kirov factory was also tested, albeit briefly. It can be penetrated in the rear from 4000 meters by the 88 mm gun and the side by the 122 mm gun.
And there you have it, the IS-3, although late to the war, would have been a dangerous opponent indeed. While the Tiger II would only be able to penetrate it from the front at 300 meters, and only aiming for the lower front plate, the IS-3 would be able to take out a Tiger II from as much as 2500 meters.