REMEMBER SEALAB? I do, but just barely, from reading about it when I was a kid. It was the US Navy's 1960's deep-sea equivalent to NASA's manned space program. (Scott Carpenter played a role in both programs). Apparently, the program also had some Cold War applications:

Although a military oath prevents SeaLab participants from describing much of their work, some details have been unclassified. Some emerged in "Blind Man's Bluff," a 1998 bestselling account of Cold War submarine espionage.

In 1971, a specially-designed submarine, the USS Halibut, reached the floor of the Soviet Sea of Okhotsk. Divers, using work pioneered at SeaLab, ventured into the depths and retrieved Soviet test missiles. They also installed a tap on a phone cable that gave U.S. intelligence officials an inside look at the Soviet Navy.

"We proved it could be done," Tomsky said.

Details of the Navy's Okhotsk cable-tapping operations emerged after the arrest of a former employee of the National Security Agency who sold the secret to the Soviets. But SeaLab's role in the affair has remained classified until recently and the full story has never been told.