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Civilian submarines are usually much smaller than military submarines. Tourist submarines work mainly in tropical resort areas or other areas with clear water and good visibility. By 1996 there were over fifty private submarines operating around the world, serving approximately two million passengers a year. Most of them carried between twenty-five and fifty passengers at a time and sometimes made ten or more dives per day. In design, these submarines borrow mainly from research subs, having large portholes for passengers' viewing and often placing significant mechanical systems outside the hull to conserve interior space. Nonetheless, even aboard tourist submarines the seating can be rather cramped. They are mainly battery-powered and very slow.

As of January 2005, the largest tourist submarine in use was the Atlantis XIV based out of Waikiki beach. The largest Atlantis-class submarine of its fleet, launched in 1994, can carry 64 passengers and 3 crew (two guides and a pilot) to 150 feet (50 m) deep off the shores of the island of O'ahu in Hawai'i. There, tourists can view a great number of ocean specimens living around artificial reefs.

In common usage, "submarine" means a ship that operates above and below the surface, untethered. Underwater vessels with limited mobility, intended to remain in one place during most of their use, such as those used for rescue, research or salvage purposes are usually called "submersibles". Submersibles are typically transported to their area of operation by surface ships or large submarines and have a very short range. Many submersibles operate on a "tether" or "umbilical", remaining connected to a tender (a submarine, surface vessel or platform).

Bathyspheres are submersibles that lack self-propulsion and used for very deep diving. A predecessor of the bathysphere, the diving bell, consisted of a chamber with an open bottom, lowered into the water. Bathyscaphes are self-propelled deep-diving submersibles reliant on a mother ship on the surface.

A fairly recent development, very small, unmanned submersibles called "marine remotely operated vehicles" (MROVs) are widely used today to work in water too deep or too dangerous for divers. For example, remotely operated vehicles (ROVs) repair offshore petroleum platforms and attach cables to sunken ships to hoist them. A thick cable providing power and communications tethers these remotely operated vehicles to a control center on a ship. Operators on the ship see video images sent back from the robot and may control its propellers and manipulator arm. The wreck of the Titanic was explored by such a vehicle, as well as by a manned vessel.