The Bulgarian naval headquarters at Sofia and Ruse according to an American CIA report dated 7 April 1954

An item reported that the headquarters of the Bulgarian navy [the so-called Voenno Morski Flot] was located in a 3-story villa on the corner Moskovska Street-Paris Street, Sofia. The headquarters of the Danube Fleet [the so-called Voenno Dunavski Flot] was located in a 4-story building with the dimensions 100x60 metres in what was in the past the Tsar Osoboditel Square, Ruse. In northern outskirts of the same town, just south of the river Danube,  was also a Danube naval detachment numbering between 800-1.000 men accommodated in barracks in an area with the dimensions 1.500x600 metres.

Source
The report was published on www.archive.org, document number CIA-RPD80-00810A000500340010-8.