The Koni class is the NATO reporting name for an anti-submarine warfare frigate built by the Soviet Union. They were known in the Soviet Union as Project 1159. The type was built during the period spanning 1975 to 1988 (14 warships) and went on to see service as largely an export product with the navies of Algeria, Bulgaria, Cuba, East Germany, Egypt, Libya, and Yugoslavia.

The profile was highly conventional with a up-swept bow and low stern section. The bridge and its corresponding superstructure were well-forward of midships. The main mast (enclosed) sat at the rear of this structure and various other protrusions were identified down the line from the bridge to the stern. The smoke funnel was well-buried within the design, attached as an aft section of the bridge superstructure. The armament consisted of two twin 76 mm AK-726 gun mountings and two twin 30mm AK-230 AA guns, twenty Osa-M SAM missiles, two RBU-6000 depth charge launchers and mine racks were fitted at the stern. The ships had 3 shaft CODAG machinery suite. The middle shaft had an 20000 hp gas turbine while the outer two shafts had diesel engines with 16000 hp in total for economical cruising. The vessel could make headway at up to 29 knots with ranges out to 2000 nmi.

Frigate Delfin laid down 21 April 1973 at the Shipyard named after A.M.Gorky, Zelenodolsk (yard No.201), launched 19 July 1975, commissioned 31 December 1975 and was assigned to the Black Sea Fleet.

Delfin Delfin was originally used for training foreign crews in the Black Sea.

Frigate Delfin was excluded from the lists of the Black Sea Fleet on 22 February 1989 and transferred to Bulgaria.