Soviet submarines for the Bulgarian navy according to a CIA report dated 1 December 1953

An item reported that two Soviet Shcha design under construction at the Progresul shipyard, Braila, Bulgaria were on 11 August 1953handed over to a Bulgarian delegation consisting of 17 officers. Since end June 1953 were the Bulgarian technical crewmembers present on the shipyard and participated in the trials. Furthermore were two Soviet M type submarines for the Bulgarian navy to be built at Braila and to be launched in April 1954.

Source
The report was published on www.archive.org, document number CIA-RDP81-01036R000100040053-9