"Basically, it's an underwater balloon. You've got two parts to it: You've got the balloon here — which is this long cylindrical object — and that's filled with a lighter-than-water substance, which is aviation gasoline," Walsh explains. "Oil floats on water, and so you get the buoyancy or lift. Then, beneath the balloon you have a cabin for the fragile humans."

History-making dive

That cabin is a 14-ton spherical steel capsule only two meters in diameter, with a single, half-meter-wide circular plastic window for viewing. There is just enough room for two people. Walsh was joined on Trieste's historic dive by co-pilot Swiss scientist Jacques Piccard — whose father, Auguste Piccard, had designed the craft.

NOAALt. Don Walsh (left) and Jacques Piccard (center) in cramped quarters inside Trieste's chamber on January 23, 1960.

On Jan. 23, 1960, the two men took the Trieste to the deepest point in the Pacific Ocean's Mariana Trench, a ravine called Challenger Deep.

The success of that mission opened the door for deep sea exploration.

Walsh grabbed an opportunity that others would later follow. "We do see bits of our DNA all over in today's underwater vehicles, both manned and unmanned, because [of] the things that we developed. Remember, everything we did was a first, not because we were pioneers or inventors, but it is literally, necessity is the mother of invention. We needed something, we had to invent it."