A bathyscaph preparing for launch

In the summer of 1964, the first tentative dives into the shallow waters of Cape Cod, Massachusetts were made by the new deep diving submarine, Alvin. The sub, built for the US Navy and operated by the Woods Hole Oceanographic Institution (WHOI), was to become arguably the most successful research submarine ever.

The dream of exploring the forbidding environment of the deep ocean goes back at least a hundred years before Alvin's launch, to Jules Verne's fabulous submarine, Nautilus. But the first people to solve the problem of protecting themselves from the crushing pressures of deep diving were Otis Barton and William Beebe. In 1932, their small, massive steel "bathysphere" was lowered to a record depth of 2,200 feet, off Bermuda.

The segment moves from Nautilus, to bathyspheres, to U-boats, to the huge bathyscaphs that reached the deepest part of the world's oceans. The ungainly bathyscaphs were not safe and practical exploration vehicles, however, as ocean explorer Bob Ballard tells Alan Alda, speaking from personal experience.

Alvin at first worked for the Navy, among other things helping recover the H-bomb lost in the Mediterranean in the 1960s. Then after a near-catastrophic sinking, the sub went on to three decades of scientific ocean exploration and discovery.