It’s a 69% attack against starting units in Leningrad. 49% if they put 1 extra inf in. So they can withdraw 5 troops on the peninsula back to Leningrad and 4 troops from Leningrad - perhaps more if they fly some planes in. In balanced mod, this theory has more merit if marines are bought G1.
The point here is that it slows the Soviet withdrawal to Bryansk. Particularly good if the southern force is sitting in Western Ukraine at the end of USSR1 - they can’t counter attack a force smashing the withdrawing Leningrad forces although may be able to hit a weak German force in Eastern Poland.