Ouch
The link I put in is to an iffy site, so feel free to Google other sources.
But, in fact, the submarine fleet didn’t have that much success apart from the attacks on ships evacuating civilians and wounded right at the end of the war. The Soviets also had a policy of targeting hospital ships (although the 3 that I mentioned don’t fall in that category).
The evil of the Soviets cannot be overstated.