Momsen served on the Navy General Board from June 1947 until May 1948. 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 also took part in developing the streamlined Albacore submarine. To avoid Navy interference, Admiral Momsen directed Bureau of Ships to design an unarmed submarine for speed, and told the Navy that the submarine would be a practice target for anti-submarine aircraft from aircraft carriers.