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.)