Submarine operators in the World War II Black Sea

Who besides Germany and the Soviet Union operated submarines in the Black Sea during World War II?

Turkey operated two British-derived boats; Hungary and Bulgaria did not maintain comparable World War II submarine forces.

The answer checks possible regional operators and distinguishes First World War memories from actual Second World War service. Hungary and Bulgaria had earlier submarine associations but no comparable operational force in the Black Sea during this war. Turkey received two S-class-derived boats that Britain had initially requisitioned and later delivered in 1942. Their transfer strengthened Turkish defenses against Germany and shows how alliance diplomacy could reverse an emergency wartime requisition.