Swiss diver, Hannes Keller, prepares to enter the diving tank at the US Naval Weapons Plant, Washington, DC in which he later submerged to a simulated depth of 700 feet. Using formulas and techniques he developed, Keller surfaced in about two and a half hours. The test was sponsored by the Office of Naval Research as part of a contract with the University of Pennsylvania. May 12, 1961.
National Archives & Records Administration