The buoyant ascent technique has been developed as a means of escape from a disabled submarine. The earliest escape devices were re-breathers of various kinds -- the famed US Momsen Lung, the German Draeger, the British BSEA. The United States, in particular, also set great store by the rescue bell, a pressure chamber traveling on a cable that would lock onto a disabled sub, receive its crew, and transport them to the rescue vessel.
Development of submarine escape devices was spurred on by controversy surrounding the sinking of the submarine S-4 in December 1927. One such device is the Submarine Escape Lung, known as the Momsen Lung, which was developed by then Lieutenant Momsen, Chief Gunner Tibbals and civilian Frank Hobson.
Charles Bowers Momsen was born in Flushing, Long Island, New York, on 21 June 1896. He attended the U.S. Naval Academy, graduating with the Class of 1920 in June 1919. Following initial service in battleships, he was trained as a submarine officer and commanded three submarines in 1923-27. Following those commands, Momsen was assigned to the Bureau of Construction and Repair. In 1929-32 he was actively engaged in the development of a submarine escape breathing apparatus that came to be known as the "Momsen Lung". The "Momsen Lung," was demonstrated successfully in a series of unauthorized experiments in the Anacostia and Potomac Rivers, and finally attracted enough favorable attention to see the lung adopted by the Navy in 1929.
For this development, he was awarded the Distinguished Service Medal, with citation which states in part: "During the early stages of its (the Lung's) design and development (he)...courageously, repeatedly and voluntarily risked his life in conducting experiments of a nature such that there was little or no information available as to their probable results. In the later tests of the device, when escapes were made from USS S-4 submerged to depths as much as 206 feet, he was not only the first person to venture the escape but also the leading and guiding spirit in all subsequent ones..."
The Momsen Lung was an oblong rubber bag that recycled exhaled air. The lung contained a canister of soda lime, which removed poisonous carbon dioxide from exhaled air and then replenished the air with oxygen. Two tubes led from the bag to a mouthpiece: one to inhale oxygen and the other to exhale carbon dioxide. The lung hung around the neck and strapped around the waist. Besides providing oxygen for the ascent, the lung also allowed a Submariner to rise slowly to the surface, thus avoid "the bends."
The device proved successful when eight Submariners used their Momsen Lungs to reach the surface from the USS Tang (SS-306), which sunk in 180 feet of water in the East China Sea in October 1944. Of the eight, five survived a night at sea, only to be taken prisoner.
The pattern of World War II's successful submarine escapes, few as they were, favored free ascent, a procedure like buoyant ascent but without a life jacket to speed the surfacing. Its chief disadvantage was the difficulty of correlating the rate of ascent with the rate of exhalation. Too much exhalation could result in drowning, too little in aeroembolism. The correlating maxim "No faster than your smallest bubble" could not always be followed under stress or in murky water. A free swimmer at depth might also not head straight for the surface.
In 1956, therefore, buoyant ascent became the standard submarine escape method of the United States Navy. Recruits were trained (at New London) and personnel requalified (at New London or Pearl Harbor) by practical exercises in a 118-foot escape tower. Before being put through these runs in the tank, they were tested in a pressure chamber to make sure that they could adjust to the equivalent of 118 feet of depth (50 pounds per square inch, as opposed to 14.7 at sea level). Then there were several hours of class-room and mock-up work before the trainees are taken to the top of the tank, where they begin with shallow ascents to practice the technique.
Finally they were tested in ascents from the 50-foot depth. With an instructor, about ten of them would enter an "escape" chamber at that depth. The instructor equalized the pressure with that in the tank by flooding and admitting air, and the occupants "equalize" as the pressure builds up. Then the hatch swings open, and each trainee in turn filled his life jacket, breathed deeply, and steped out into the tank. Scuba divers watched his bubble stream to determine -- as a safety measure and for purposes of evaluation--whether he is exhaling properly. Two successful runs were required for qualification. The psychological assurance and real value gained from mastery of the buoyant ascent technique were out of all proportion to the one and a half days spent in training for submarine escape.
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