USS Segundo (SS-398) was a , of the United States Navy named for the segundo, a cavalla fish of Caribbean waters. Construction and commissioning Segundo was laid down on 14 October 1943 by the Portsmouth Navy Yard in [Kittery, Maine, launched on 5 February 1944, sponsored by Mrs. John L. Sullivan, and commissioned on 9 May 1944. May–August 1944 Segundo completed fitting out and contract trials then moved to New London, Connecticut, on 15 June and began training. The submarine stood out of New London on 26 June for the Panama Canal Zone en route to the Pacific war zone. She departed Balboa on 9 July and arrived at Pearl Harbor on 25 July. The next several weeks were spent in training exercises and weapons firing. The ship was combat loaded on 19 August and 20 August and, the next day, sailed on her first war patrol. First and second patrols, August 1944 – January 1945 Segundo, together with submarines , and formed a wolf pack. They refueled at Saipan on 3 September and departed the next day for their patrol area in the Philippines near Surigao Strait. She was in the Philippine Sea east of Catanduanes Island at on 13 September 1944 when two U.S. Navy planes mistook her for a Japanese submarine and strafed her as she crash-dived. No rounds struck her. Segundo found no worthwhile targets were found during the patrol, and she ended it at Majuro Atoll in the Marshall Islands on 21 October 1944 without having fired a shot. The second patrol, from 16 November 1944 to 5 January 1945, was more profitable. Segundo, and sister boats , and were cruising between Luzon Strait and the South China Sea. On the evening of 6 December, a convoy of seven escorted merchant ships was sighted. The three submarines made night attacks which sank all of the merchantmen. Third patrol, February–March 1945 Segundo refitted at Guam from the submarine tender and was in the East China Sea with Razorback and on 1 February. Three torpedo attacks were made on unescorted ships near the Korean coast in shallow water. The first attack was on 6 March against a small ship but all torpedoes missed. The next was made four days later against a medium-sized ship. Four torpedoes were fired at but they also missed. The third attack was a night surface action against a cargo ship on 11