Diodon (SS-349) was launched 10 September 1945 by Electric Boat Company, Groton, Connecticut; sponsored by Mrs. D. Cullinane; and commissioned 18 March 1946.

It received an extensive GUPPY II modernization at Mare Island Naval Shipyard between August 1947 and March 1948.

It trained frigates of the Republic of Korea in antisubmarine warfare in Sagami Wan, Japan, and from 30 October to 28 November made a simulated war patrol.

Resuming its west coast operations, Diodon aided in the training of Canadian naval air and surface forces out of Esquimalt, British Columbia, from October to December 1952.

During its 1956–1957 tour of duty in the Far East, Diodon visited Brisbane, Australia, for the celebration commemorating the World War II Allied victory in the Battle of the Coral Sea in May 1942.