[Little Ray]

It wasn’t that version of the Mk4 in use at the time of Barbarossa. It was the short barreled infantry gun version.
At the time of Barbarossa the German main battle tank was the Mk3 with a 37mm or 50mm main gun. That was inadequate for KVs and T-34s.
If the Germans had the long barrel PAK version of the Mk4 things would had gone much better!

[BroJoeK]

Thanks for the history lesson!