Bulgarian and Soviet navies visiting each other naval bases according to a CIA report dated 4 September 1953

An item reported that small vessels of the Soviet Navy regularly visited the naval base at Varna and Burgas in Bulgaria while Bulgarian warships visited at their turn Soviet naval bases especially the one at Sevastopol [nowadays Ukraine]. Bulgarian naval personnel was trained the Soviet Union in naval warfare.

Source
The report was published on www.archive.org, document number CIA-RDP80-00810A002200170042-3