The audio recording is funny: In trying to connect, via telephone, President Lyndon Johnson to Scott Carpenter (the Mercury astronaut of Right Stuff fame who joined the SEALAB program), the U.S. Navy tries to explain the effects of breathing helium on the voice of Carpenter to a reluctant White House secretary.

At the end of 1965, an underwater version of a space station called SEALAB II was set up on the Pacific Ocean seabed about a mile offshore from La Jolla, near San Diego, California. According to author Ben Hellwarth, divers lived for days at a time in SEALAB II, "a 200-ton prototype that was about the size of a city bus and looked something like a customized railway tank car."

His story is on The Huffington Post's Science section.

"The divers who (bravely!) volunteered to become 'aquanauts' — a descriptor for sea-dwelling humans that never really caught on — faced dangers that rivaled those of their space-bound counterparts, in part because they were trying out a novel method called 'saturation diving,'" says Hellwarth.

Hellwarth describes the work of these largely forgotten aquanauts in his book, Sealab: America's Forgotten Quest to Live and Work on the Ocean Floor, available on Amazon.

For more science-related stories, visit The Huffington Post.