Submersible craft are useful in situations where unprotected divers would be at risk from such dangers as predators (like sharks), the pressures of very deep water, or strong currents. Submersibles are routinely put to work on industrial, scientific, and military tasks. They aid industry in conducting undersea surveys, searching for new mineral deposits, performing salvage, and monitoring installations such as oil rigs and dams. Scientists use submersibles to explore geologic sites and areas of activity between tectonic plates (areas where the large plates that make up the earth’s surface are moving). Scientists also use submersibles to explore marine biology and perform undersea archaeology. Some small submersibles have been built for tourism. These range greatly in size, but most hold from 15 to 50 passengers.
The United States military remains the most active sponsor and operator of advanced submersible craft. United States Navy submersibles are used for salvage operations, submarine rescues, delivering navy commandos underwater, and minesweeping (detecting explosive underwater mines). Since the 1950s there has been a close relationship between U.S. Navy organizations responsible for developing deep-ocean submersible craft and civilian scientists who have used the same craft for scientific and historical research. New technology has also allowed a number of new civilian firms to develop and market ready-to-use submersible technology for commercial purposes.