[1] It was aboard S-1 Momsen's attention became drawn to the urgent need for a way to rescue trapped submariners.

[1] On September 25, 1925, S-1's sister ship, S-51 (SS-162), collided with freighter City of Rome in the vicinity of Block Island and sank in 130 feet (40 m) of water.

After the 1927 S-4 incident, Momsen began working on a device to help trapped submariners escape safely to the surface.

[1] Officially called the Submarine Escape Lung, it consisted of an oblong rubber bag that recycled exhaled air.

[2] The local press enthusiastically received the "new" device and they dubbed it the "Momsen lung", a name that stuck in the US.

In 1929, Momsen received the Navy Distinguished Service Medal for personally testing the device at a depth of 200 feet (61 m).

The Momsen lung saved its first lives in October 1944, when eight submariners used it to reach the surface after Tang (SS-306) sank in 180 feet (55 m) of water in the East China Sea.

He built a prototype, constructed from a water-tight aircraft hangar pirated from S-1 and tested it off Key West, Florida.

From 1937 to 1939, Momsen led an experimental deep-sea diving unit at the Washington Navy Yard which achieved a major breakthrough in the physiology of the human lung's gas mixtures under high pressure.

Also, divers who ascend too rapidly can get decompression sickness, commonly known as "the bends," which happens when nitrogen in the blood forms bubbles.

In experiments often performed by Momsen himself, the team replaced the nitrogen with nontoxic helium and mixed it with varying levels of oxygen depending on the depth.

He also supervised rescue chamber operators[4] as it made four dives to bring the submariners to the surface and a fifth to check the flooded aft section for survivors.

Along with Commander McCann, Momsen received a letter of commendation from President Franklin D. Roosevelt for the successful rescue of the crewmen from the Squalus and the subsequent salvage of the submarine.

[1] While Momsen was ComSubRon 2 in the U.S. Pacific Fleet, captains under his command reported their Mark 14 torpedoes were not functioning properly.

He took torpedoes to the shallow waters and sheer cliffs of the Hawaiian Island of Kahoolawe and fired until he got a dud.

[6] He also developed a simple code for communications on the short range VHF radio system used for Talk Between Ships (TBS).

[6] The pack consisted of Edgar McGregor's Shad, experienced skipper Dave White's new Cero, and Grayback, fresh from refit in Mare Island (and with one of the Submarine Force's first 5 in (127 mm) deck guns), under newcomer John Moore.

He served as Assistant Chief of Naval Operations for Undersea Warfare from 1948 to 1951, then became Commander of the Submarine Force's Pacific Fleet.

Momsen Hall, the 75-man Bachelor Officer Quarters at the Atlantic Undersea Test and Evaluation Center (AUTEC), Andros Island, Bahamas, was named in his honor in 1969.