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Career
Ordered:
Laid down:
Launched:
Commissioned:
Decommissioned:
Fate:	wrecked by fire and sunk
Homeport:
Stricken:
General Characteristics
Displacement:	460 tons surfaced, 540 tons submerged
Length:	56.0 metres (183 feet 9 inches)
Beam:	5.1 metres (16 feet 5 inches)
Draught:	3.8 metres (12 feet 6 inches)
Propulsion:	Kreislauf system: two 700 hp conventional diesel engines, one 900 hp AIP (LOX) diesel engine, one electric creep motor; three shafts
Speed:	18 knots surfaced, 16 knots submerged
Range:	2750 nautical miles at cruising speed on surface
Complement:	30 officers and men
Armament:	four 533mm (21-inch) torpedo tubes in bow, eight anti-submarine/anti-ship torpedoes

M-256 as a Project 615 (also known by the NATO reporting name of "Quebec"-class) short-range attack diesel submarine of the Soviet Navy. She was commissioned into the Baltic Fleet.

Quebec-class submarines were fitted with two regular diesel engines and a third, closed-cycle diesel engine, which used liquid oxygen (LOX) to provide air-independent propulsion while the submarine was submerged. This system produced remarkable submerged speed and range, and greatly increased the hazard of a fire. Quebecs were referred to by their crews as "cigarette lighters."

On 26 September 1957, while operating in gale conditions in the Tallinn Gulf of the Baltic Sea, one of M-256’s diesel engines exploded. Fire immediately engulfed the diesel compartment, and soon spread to the next next compartment. The boat surfaced and because of the likelihood of further explosions her crew evacuated onto her weather deck. None of the four ships keeping station nearby were able to take her under tow or evacuate her crew because of the gale conditions. About four hours after the beginning of the fire the boat suddenly lost longitudinal stability, took on a steep down-bubble, and sank. Of the 35 men on the boat's deck, only seven were rescued.

References

• Книга памяти - M-256