Special trials ship for the Navy, built on the basis of Project 264 seagoing minesweeper. The vessel is designed for serial and control tests of various torpedo weapons. There are some torpedo tubes aboard the ship. The series of these vessels consisted of 4 hulls.

The ship has 71,7 m length overall, beam of 9,4 m, and displacement 943 tons at full load. The ship has diesel propulsion system with a two 2600 hp 40D diesel and two shafts. The vessel has a speed of 16 knots, a range of 2500 nmi at 12 knots and an endurance of 10 days. The vessels are also equipped with Don navigation radar.

Trials ship OS-138 laid down at the Shipyard named after A.M.Gorky, Zelenodolsk, commissioned in 1974 and was assigned to the Black Sea Fleet.

Now in service.