Accompanying the U.S. invasion of the Marianas in mid-June 1944, Lockwood sent more than a dozen submarines westward to interdict possible Japanese reinforcements. "Seahorse" departed Brisbane on 3 June for her fifth war patrol and took station with in the Surigao Strait between Mindanao and Leyte 13 June. "Seahorse" greatest contribution to the Battle of the Philippine Sea was locating a Japanese battle group centered around the Japanese battleships "Yamato" and ""Musashi". In 1997, Cutter told a reporter the task force was too distant to catch, but he sent a routine contact report.