One of the first uses of the IS-85 tank was in the Korsun Pocket. The 13th Guards Heavy Tank Regiment, equipped with brand new IS-85s, was sent to block Kampfgruppe Bake (an unusual formation equipped with both Tiger and Panther tanks) from breaking through to the pocket. Forczyk describes this engagement as not particularly favourable to the IS tanks.
"These heavy tanks were committed into action on 15 February and unwisely attacked Kampfgruppe Bake instead of sitting on the defense; the Panthers and Tigers knocked virtually all of them out. Following this incident, the GABTU resolved to upgrade the new IS-series heavy tanks to the 122 mm gun."
Oof, that's quite a mistake for a book published in 2015. The decree titled "On IS tanks" authorized the production of an IS tank armed with a 122 mm gun in September of 1943. By February 15th, these tanks were not only in production, but had already reached the front lines.
However, there's something else fishy in play here. This unit that was destroyed by Tigers and Panthers mysteriously pops up on the very next page to wreak havoc on Kampfgruppe Bake and Frank's attempts to break through to the encircled men. Let's take a look at what actually happened.
The 13th Guards Heavy Tank Regiment was formed only on February 13th, 1944, from the 13th Guards Heavy Tank Breakthrough Regiment. Like Forczyk says, it was armed with 21 brand new IS tanks. The regiment was attached to the 2nd Tank Army. However, there is a big problem here. There is no mention of a 13th regiment in the journal entry for February 15th. The entry for February 16th reveals why:
"31 SU-76 SPGs will arrive near Medvin (25 of them are meant for the 2nd TA). There will also be the 13th Heavy Tank Regiment there (IS-85) which will be subordinated to the 2nd TA. Put the 13th HTR near Dzhurzhantsy, with the goal of preventing the enemy from reaching Pochepyntsy. When using the 13th HTR, take measures to retain complete secrecy and do not, in any circumstance, leave a knocked out tank for the enemy. For this reason, cover the flanks of the regiment by any means and prepare evacuation and demolition equipment."
On February 15th the tanks simply had not yet arrived on the battlefield, making them quite difficult to destroy. However, maybe the Germans wrote the date down wrong, or these were IS tanks from another unit, or the IS tanks were attacked on the march, anything can happen in war. Let's take a closer look at the next few days.
"The 2nd Tank Army received the 13th Heavy Tank Regiment with IS tanks on February 17th, 1944, and the 8th Heavy Tank Regiment on February 19th.
During its time in the 2nd Tank Army, the 8th HTR did not participate in combat.
On 17-18th of February, 1944, the 13th HTR received the objective of destroying an enemy column that has broken through. Losses were dealt to the enemy: up to 650 soldiers and officers. The regiment did not suffer any losses in materiel or personnel.
19 tanks were in service, 2 tanks were in repairs for technical reasons. One tank had a welding seam on a gearbox connecting link rupture when the tank struck a mine. The the other one had its rotor break."
That's it. Not only did the Panthers and Tigers not knock out "virtually all" of the IS tanks that were sent to defeat them, they did not destroy any.