source: CIA report dated 14 November 1957 80T00246A038500490001-1
An item reported that the Bulgarian navy possessed 18 submarine chasers divided over 4 squadrons.
There were 2 Rilla-class vessels with a displacement of 200 tons.
Further more were the Belomorets and Chernomorets purchased in 1922 still in service with a displacement of 77 tons, dimensions 32 x 4,3 x 1,8 metres, diesel engine supplying 660hp allowing a speed of 17 knots, arrange of 700 miles with a speed of 10 knots, a crew numbering 26 men and an armament consisting of 1-4,7cm gun, 2-3,4cm guns, 1-2cm gun and 2 depth charge launchers.
There were also the as gunboats classified Maritsa and Vardar.
Of the BO (Bolshoy Okhotnik) large patrol vessels-class were in 1947 by the USSR handed over the BO-1 and the Bo-2 in service. With a displacement of 95 tons, dimensions 83 x 5 x 2 metres, the diesel engines and 2 screws allowed a speed of 15 knots, a crew numbering 28 men and an armament consisting of 1-4cm gun and 2-2cm guns. A remark suggested that it were possible 280 ton patrol boats which were acquired by the USSR between 1941-1945.
An there were 5 small patrol vessels of the MO (Malenkil Okhotnik) class in 1947 handed over by the USSR with a displacement of around 50 tons, as dimensions 27 x 4,5 x 1,5 metres, a diesel engine allowing a speed of 20 knots, a crew numbering 8 men and armed with 2-2cm guns.
Source
The report was published on www.archive.org, document number by CIA-RDP83-00415R012700120006-
