Photo #36. Turret of the assault gun "Ferdinand" hit by 122 mm shells.
1. Dent 100 mm deep, a bump formed on the other side. Armour thickness here is 200 mm.
2. Penetration, the shell is stuck. Armour thickness here is 150-180 mm. Distance: 1400 meters."
The Ferdinand is a formidable opponent, even for the powerful D-25 gun. However, we see the flaw in Soviet penetration metrics. The shell that penetrated the Ferdinand penetrated the armour, and produced spalling that would have killed the crew. And yet, the shell itself is stuck in the armour. This does not count as a penetration by Soviet standards. If you look at the table of penetrations, the IS-2, theoretically, cannot penetrate this much armour.
Let's see how these test results apply to real life. An IS-2 from the 71st Guards Heavy Tank Regiment of the 3rd Guards Tank Army encountered a Ferdinand belonging to the s.Pz.Jg.Abt 653 on July 22nd, 1944, near the city of Magerov. From the report:
"At 13:30, the regiment received a new objective: the 53rd Guards Tank Brigade was to move toward Nogortse, Veryny, Turnnko, Dobrosin, Magerov, Shezehts, Yavorov, and must be ready to deflect a counter-attack from the Zhulkev and Nemirov direction.
In the region of Nogortse and Turnnko, about 15-20 km in the march, the terrain became extraordinarily difficult for heavy tanks, due to a large amount of swamps, lowlands, and completely destroyed roads. Due to this, the regiment crossed this section all night, and only made it to the highway at Dobrosin in the morning.
Moving forward, elements of the brigade were ambushed next to Magerov. Without engaging, the attacking forces were ordered to go around Magerov from the North-East, and regroup at their original destination 3 km away from Magerov. At the same time, a platoon from Ryzhinkiy's tank company, acting with the 53rd Tank Brigade, was ordered to destroy the ambush, and clear the road to Nemirov.
Lieutenant Slunayev's tank, under the cover of another tank, moved to the crossroads north of Shestaki, and observed the enemy ambush for 10-15 minutes. It was thoroughly camouflaged on the clearing in the forest south of Borki. After detecting all threats, Slunayev's tank opened fire from 1000 meters, and destroyed it in several shots. As a result, a Ferdinand SPG and an APC were burned, along with 2 guns. The path to Magerov was open."