After shakedown off Portsmouth, N.H., and New London, Conn., "Sea Owl" transited the Panama Canal and arrived at Pearl Harbor on 23 October 1944. Her first war patrol commenced on 19 November and was conducted in the East China Sea as part of a coordinated attack group with and . She carried trial versions of Mark 18 electric and Mark 27 ("Cutie") homing torpedoes. After three weeks of searching for worthwhile targets, "Sea Owl" sank her initial victim, a Japanese destroyer escort, with one Mark 27. She followed with a second escort, stopped by a Mark 27 and finished off with one Mark 18, from about 1000 yd (910 m). This was the first combat success for both weapons. The remainder of the patrol was uneventful, and the submarine put into Guam on 15 January 1945.