For the 88mm Flak gun, it was about the only thing germans had to stop the russians heavy tanks. It was later on litterally used on the Tiger II mounted in the turret. So yea, it was an awesome gun.
Slighty out of topic, i came on this article on the KV heavy tank which gives an idea of what a russian heavy tank could do:
"On August 14, the German 8th Panzer Division’s vanguard ventured directly into the well-prepared Soviet ambush, with Kolobanov’s tank knocking out the lead German tank with its first shot. The Germans falsely assumed that their lead tank had hit an anti-tank mine, and failed to realize that they were ambushed. The German column stopped, giving Kolobanov the opportunity to destroy the second tank. Only now did the Germans realize they were under attack, but failed to find the source of the shots. While the German tanks were firing blindly, Kolobanov knocked out the trailing German tank, thus boxing in the entire column.
Although the Germans correctly guessed the direction of fire, they could only spot Lieutenant Kolobanov’s tank, and now attempted to engage an unseen enemy. German tanks moving off the road bogged down in the surrounding soft ground, becoming easy targets. 22 German tanks and 2 towed artillery pieces fell victim to Kolobanov’s No. 864 before it ran out of ammunition. Kolobanov ordered in another KV-1, and 21 more German tanks were destroyed before the half-hour battle ended. Total number of destroyed German tanks reached 43, and this was done by five Soviet KV-1 (two more remained in reserve).
After the battle, the crew of No. 864 counted a total of 135 hits on their tank, none of which had penetrated the KV-1’s armour. Lieutenant Kolobanov was awarded the Order of Lenin, while his driver Usov was awarded the Order of the Red Banner. "
