Project 615 Quebec class
In the early 1950s, Central Design Bureau #18 developed the Project 615 small submarine (NATO designation Quebec) with a normal displacement of 406 t. It was provided with a closed cycle diesel, which allowed it to significantly increase the submerged endurance and speed. Following the type submarine, 29 subs were series-built according to corrected Project A615. Till the mid-1990s, Project 615 subs were the world's sole series-produced submarines with air independent propulsion (AIP) plants and remain, as before, the sole series-produced nonnuclear submarines provided with unified engines that are equally suitable for surface and submerged running.
The first Soviet-designed air-independent propulsion (AIP) system used liquid oxygen and diesel fuel to operate a closed-cycle diesel (CCD) engine. This was based on prewar Soviet work on closed-cycle diesels undertaken by S.A. Basilevskiy of CKB-18. The powerplant developed in this effort was designated REDO. The exhaust from the diesel was compressed and the carbon dioxide extracted for dumping overboard. The purified exhaust gases were then refreshed with oxygen from a liquid oxygen tank and recycled through the engine.
A prototype was installed in the submarine M-401 for an experiment that lasted from 1940 to 1945. Soviets continued development for 15 years after World War II. Using data generated from the work during WWII, they built 30 Quebec-class submarines from 1953 to 1957.
Quebec submarines were fitted with two diesel engines for running on the surface. A third, closed-cycle diesel engine, using liquid oxygen and recycled exhaust gases, ran the submarine while submerged. This gave the Quebec-class submarines very good submerged speed and range. The liquid oxygen system was the source of frequent fires, and the Quebec-class boats came to be known as "cigarette lighters" by their crews.
The submarines were modernized in the late 1950s as Project M615 but they remained susceptible to fires and were generally distrusted throughout the fleet. Ironically, by this time, the Project M616 boats were exhibiting some quite remarkable performance capabilities. In 1961, M-321 completed a fully submerged voyage around the Baltic, a feat repeated by M-356 in 1962. Such journeys were far beyond the abilities of conventional diesel electric submarines of that time.
The Quebec-class submarine M-256 sank on 26 September 1957, after an explosion and fire in the liquid oxygen system. Following the initial explosion, the submarine surfaced and the crew evacuated to the deck. Despite firefighting efforts, the fire spread to an adjacent compartment. Very poor weather conditions prevented nearby vessels from rendering aid. After four hours, the submarine suddenly lost stability and sank, with only seven of the 35 men on deck surviving.
The Project 615 boats were roughly comparable with the German Type 205 class submarines but they have no real Western counterpart in technology. Their AIP diesels were about a quarter century ahead of any comparable Western design and, had the Soviet navy continued with the program, they would have been the foundation of a diesel electric fleet of menacing capabilities. Eventually, this system was removed from the submarines and replaced with a third, conventional diesel engine.
Development efforts were terminated in the mid-1970s, and the remaining Quebecs were scrapped. They had achieved much greater submerged endurance and range, but those gains were cancelled out by the unsafe nature of their AIP systems. The concept was abandoned and, with it, one of the very few areas where Soviet submarine technology was far ahead of the west.
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