Soviet submarine S-99

The S-99 (С-99) experimental submarine was the only ship of Whale class (known locally in the Soviet Union as Project 617) that the Soviet Union built during the early cold war period and the only soviet submarine which had a Walter engine fuelled by high test peroxide (HTP).

Design
Initial design of submarine was based on project XXVI documentation taken from Germany as a trophy in 1945 and used in the 1945–1946 development of Project 616. The resultant speed of 19 knots submerged and a 10% buoyancy reserve were assessed as a good but insufficient result, leading to a new project from 1949–1951 based in Leningrad.

Construction
The hull of the submarine was divided on six sections
 * 1) torpedo room
 * 2) battery and living quarters
 * 3) command room
 * 4) diesel room, maintenance base of the turbine engine
 * 5) turbine room, unoccupied and sealed
 * 6) electric engine room

Soviet Navy service
The boat was built in 1951-52 and commissioned in 1956 after sea trials. S-99 became the fastest Soviet submarine of the time, reaching 20 to 22 kn submerged. Between 1956-59 she served in the Baltic fleet. In 1959, prior to planned repairs, S-99 was used for turbine tests. Experiments at depths of 40 to 60 m were successful, but there was an explosion at 80 m. The submarine surfaced and reached base on battery power. After the incident, S-99 was decommissioned and scrapped.