The S-99 () experimental submarine was the only ship of the Project 617 class (codenamed Whale) that the Soviet Union built during the early Cold War. She was the only Soviet submarine which used a German Walter turbine fueled by high-test peroxide (HTP). Entering service in 1956, the boat was assigned to a training unit of the Baltic Fleet. S-99 was badly damaged by a HTP explosion in 1959 and was not repaired. The submarine was decommissioned in 1964 and subsequently scrapped. Background At the end of the Second World War, the Soviets captured components for the HTP-fuelled Type XXVI submarine as well as engineers and technicians who had worked on the Walter turbine that used HTP. To make use of this new technology, they established a new submarine design bureau in Germany headed by Engineer-Captain Aleksei A. Antipin, formerly head of Central Design Bureau No. 18 (TsKB-18), which was tasked with the collection of plans and documents relating to the Type XXVI and its components. TsKB-18 began designing a copy of the German submarine as Project 616 in 1946, intending to order components from East Germany, but this was rejected by the Soviet Navy as it did not meet Soviet standards for reserve buoyancy and other issues. Together with the Central Research Shipbuilding Institute No. 45, the bureau immediately then began an original design utilizing the Walter HTP turbine. Preliminary design work on Project 617 was finished at the end of 1947. A new design bureau for high-speed submarines (SKB-143) was established on 30 March 1948 and the Antipin Bureau was folded into the new organization with Antipin in charge. Knowing that the Walter HTP turbine technology was unproven, he decided to construct the submarine's propulsion plant and its hull compartment in a building at the Sudomekh Shipyard in Leningrad. The turbine used original German-built components as much as possible and was tested through the beginning of 1951. It was carefully disassembled in May and repaired as necessary in preparation for installation in S-99 which had begun construction a few months prior. Description S-99 was a double-hulled submarine that displaced on the surface and submerged. The boat had an overall length of , a beam of and a draft of . S-99s crew numbered 51 officers and men. Her hull was divided into six compartments; the sail was very small and did not have a compartment. The hull was