In 1966, 10 days after a U.S. plane carrying four nuclear bombs had run into another and crashed into Spain, the Department of Defense was not yet ready to admit that they were missing a bomb. There was clearly a search on, out off the southern coast of Spain, but "the department, which officially has declined to confirm that any hydrogen bombs were missing, also declined to specify the purpose of 'the search,'" the New York Times reported.
The department would confirm that it was preparing to send over the Aluminaut—a submersible vehicle built by Reynold Metal Company and on contract with the Navy—and possibly the Alvin, a deep submergence vehicle that could take a small crew down to the depths of the ocean.
In the 1960s these were new creations. The Aluminaut was built in 1964, the same year Alvin arrived at Woods Hole.
Just a couple years before, it had only been an idea:
Vehicles like these were enabling people to see more of the ocean than they ever had before. Just six years earlier, in January 1960, the Trieste took a crew of two deeper than ever before—more than 35,000 feet down, into the Mariana Trench.
To find the missing hydrogen bomb—there was, indeed, one missing—the Navy brought not just the Aluminaut and the Alvin, but also a version of the CURV, a cable-controlled underwater recovery vehicle to actually grab the bomb and bring it back up. Eventually Alvin found the bomb, but the Navy dropped it while trying to bring it back up to the surface. Alvin found it again, but when the CURV went to retrieve it, the recovery vehicle got tangled in the weapon's parachute. The Navy hauled the whole mess up, until divers could reach it and transfer it to a bridle attached to the ship. "The long lost nuclear weapon was swung aboard, and gentle lowered to a wooden cradle," the DoD would later report.
Today, there are remotely operated underwater vehicles working all over the world. Like the CURV, these devices are connected to their operators by a tether, probing the depths of the ocean sometimes for science, and many times in service of deep-sea oil drilling. There's even an OpenROV project that created a kit that lets anyone with a few hundred dollars to spare build their very own underwater robot to explore the ocean. It can't quite get all the way down to the depths of the Mariana Trench, but, hey, we can't all be James Cameron.