A "remotely operated vehicle" (ROV) usually is defined as a tethered, unmanned submersible. That is not entirely correct. Man is still in the loop, but on board a surface support vessel rather than in the vehicle. Here the "pilot" flies the vehicle using sensor inputs and TV imagery from the submersible.
U.S. Navy research and development produced the first practical ROVs in the early 1960s. By the middle of that decade the first Navy operational ROV was put into service. This was CURV, "Cable-controlled Underwater Recovery Vehicle," developed to help recover experimental underwater ordnance from offshore test ranges. CURV became famous when it helped recover a lost hydrogen bomb off Palomares, Spain, in 1966 and saved three men trapped in a submersible off Ireland seven years later.