Small navy vessels arrived at Russe, Blugaria according to a Cia report dated 29 May 1951

An item reported that at Russe or Ruse , Bulgaria in mid October 1950 between 10-15 small boat arrived with an armament varying between one small gun or 2 medium calibre machineguns.

Source
The report was published on www.archive.org, document number CIA-RDP82-00457R007600470023-6