The Black Sea is another area where I don’t remember reading or hearing a lot about battles during WW2.
There were several, but the Soviets basicly controlled the Black Sea throughout the war, despite sometimes heavy losses from Axis aircraft.
The Germans would eventually move several older submarines OVER LAND, to Romania, in to the Black Sea, but the results would never justify the cost of getting them there.
Italian E-Boats would have more success.