final war patrol, Threadfin rescued three survivors from a downed American flying boat and took them to Guam where she arrived on 27 July. Post-war activities From 27 July to 12 August, the submarine refitted at Guam in preparation for her fourth war patrol, but that patrol never occurred. While she conducted post-refit training, the Japanese capitulation ended hostilities. On 18 August, she got underway from Guam to return to the United States. She transited the Panama Canal on 16 September and reported for duty with the Atlantic Fleet. Six days later, she tied up at the naval base at Staten Island, New York. The balance of Threadfin’s 28-year career proved to be routine in nature. Initially, she operated out of New London, Connecticut, serving as a training platform for the officers and men learning the ropes at the Submarine School. That duty apparently lasted until December 1952, at which time the submarine was decommissioned to enter the Portsmouth Naval Shipyard for an extended conversion overhaul. Over the next eight months, Threadfin received extensive modifications in an effort to make her more effective in underwater operations—more truly a submarine than simply a submersible. When she emerged from the shipyard the following summer, her hull had been streamlined and her sail modified. In addition, she lost one of her four diesel engines to make room for auxiliary equipment displaced by an expanded sonar facility. Finally, her underwater performance was boosted by the installation of two "greater capacity" batteries—they actually produced the same power as the old style batteries but in a smaller, lighter physical plant—and a snorkel for extended submerged cruising. At the completion of her Greater Underwater Propulsion Power Program (GUPPY) conversion, Threadfin was recommissioned at Portsmouth on 7 August 1953. In October, she conducted her post-conversion shakedown cruise and, early the following month, reported for duty as a unit of Submarine Squadron 4 at Key West, Florida. Over the remaining 19 years of her career, Threadfin operated off the East Coast. She participated in several exercises each year and frequently conducted summer training cruises for United States Naval Academy and NROTC midshipmen. Though based in Key West, she made visits to ports on the Gulf of Mexico such as New Orleans, Louisiana, and often ventured north to New London, Connecticut. In October 1962, she participated in President of the United States John F. Kennedy's quarantine of Cuba during the