In Russia there has been no lack of technical competence regarding the design and building of underwater vehicles—witness the Soviet production of more than 400 nuclear submarines during the Cold War.
Yet during most of the 1945–91 period, the Soviet Union never had more than three or four fully operational manned submersibles. Beginning with tethered vehicles in the mid-1950s, Russian “home-built” submersibles were very basic and not very successful in use. Open literature states that most of the early vehicles were used for fisheries research; in reality, they were probably used for military purposes. (Fisheries researchers in the West did not use manned submersibles.)
Operational success came from buying manned vehicles from outside the Soviet Union. In the mid-1970s, HYCO International in Canada built two Pisces-class submersibles for the Soviet Academy of Sciences. Operated by the P. P. Shirshov Institute of Oceanology, they were capable of diving to 6,500 feet. One of their best-known expeditions was to Lake Baikal in Siberia, the world’s deepest lake. There the Pisces dove to the deepest spot, 5,387 feet.