ROVs
Small unmanned submersibles called "marine remotely operated vehicles" or MROVs are widely used today to work in water too deep or too dangerous for divers.
Remotely operated vehicles (ROVs) repair offshore oil platforms and attach cables to sunken ships to hoist them. Such remotely operated vehicles are attached by a tether (a thick cable providing power and communications) 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.
Read more about this topic: Submersible