The submarines of the Bulgarian navy according to a CIA report dated 13 November 1952

An item reported that in the Soviet Union handed in 1947 three submarines each above the 500 tons over to Bulgaria and which were stationed in the Soviet harbours of Odessa [Ukraine] or Ochakov [Ukraine]. The command and headquarters of this flotilla was situated at Ochakov although the submarines were Bulgaria-flagged and with Bulgarian crews.

Source
The report was published on www.archive.org, document number by CIA-RDP83-00415R012700120006-1