Momsen lung

The Momsen lung was a primitive underwater rebreather used before and during World War II by American submariners as emergency escape gear. The Momsen lung was invented by Charles B. Momsen (nicknamed "Swede"). Submariners would train in a 100 ft deep escape training tower using this apparatus. It was first introduced as standard equipment on P- (Porpoise-) and Salmon-class boats.

The device recycled the breathing gas by using a counterlung containing soda lime to scrub carbon dioxide. The lung was initially filled with oxygen and connected to a mouthpiece via twin hoses containing one-way valves: one for breathing in and the other for breathing out.

The only known emergency use of the Momsen lung is during the escape from USS Tang (SS-306) on 25 October 1944. Thirteen men (of thirty survivors) left the forward escape trunk: five were picked up by the Japanese; three more reached the surface "but were unable to hang on or breathe and floated off and drowned"; the fate of the other five is unknown. Not all the escapees from the trunk used the Momsen lung. An officer had his mouthpiece knocked out shortly after leaving the submarine. One of the trunk ascents was made without a Momsen lung. Many were unable to leave the trunk or discouraged from attempting an escape. Most of the crew perished.

The Royal Navy used a similar device, the Davis Submerged Escape Apparatus, but it was clumsy to use. The Royal Navy later adopted the practice of blow and go, in which the sailor would exhale continuously during ascent to avoid air expanding in the lungs, which could cause them to rupture. Postwar, submariner Walter F. Schlech, Jr., among others, examined submerged escape without breathing devices and discovered ascent was possible from as deep as 300 ft: "in one sense, the Momsen Lung concept may have killed far more submariners than it rescued".