Beebe tests the 4500-pound bathysphere for leaks.

The submersible Alvin has made more breakthrough deep-sea discoveries than any other sub. Vessels like Alvin are the culmination of a long evolutionary period, during which many brave scientist/inventors joined the quest to explore the deep ocean.

In the 1930s, a pioneering engineer named Otis Barton became the first to find real deep-diving success with his creation of the four-foot-in-diameter steel "bathysphere." Barton and his partner, William Beebe, used the craft to perform a series of dives off the coast of Bermuda, eventually reaching a record-breaking 3028 feet. Theirs was mankind's first glimpse at life far below the ocean surface. Beebe's astonishing descriptions read like science fiction to the experts of the day.

The bathyscaph reached the 35,000-foot Challenger deep off Guam.

Also in the 1930s, a Swiss balloonist named August Piccarde built a vessel that could voyage even deeper. Unlike the bathysphere, which had to be tethered to the surface, this larger submarine called the bathyscaph relied on its own gasoline floatation tank, allowing greater flexibility as well as greater depths. But explorer Bob Ballard found out first hand that this unwieldy vessel could also be dangerous. During one dive, he tells Alan, he and a crew ran into trouble near the bottom. They managed to bring the crippled sub up in a tense, six-hour ascent.

Thanks to further technological innovations in the 1960s, smaller, more maneuverable submersibles were created, leading to the Alvin. Aboard this vessel, Ballard turned the world of deep-ocean exploration on its head with the discovery of the Galapagos vents.

Into the Deep...Part Two - Remote Control Exploration