the results of her latest attack as the cargo ship, Toei Maru, slipped beneath the waves. Seahorse terminated her third patrol at Pearl Harbor on 16 February. Fourth war patrol, March – May 1944 Seahorses fourth war patrol was conducted in the Mariana Islands. She departed Pearl Harbor on 16 March 1944 and intercepted a large Japanese convoy on 8 April. After nightfall, the submarine launched four torpedoes at overlapping targets, sinking the converted seaplane tender . Shortly thereafter, her second spread of torpedoes damaged the cargo ship , which subsequently was towed to Apra Harbor on Guam for repairs. Although a counterattack by escorting destroyers drove Seahorse from the vicinity, she quickly regained contact and continued the chase into the following day, sinking the cargo ship Bisaku Maru. Seahorse took up a lifeguard station for the carrier airstrikes on Saipan that commenced on 12 April 1944. Some sources credit her with sinking the Japanese submarine west of Saipan on 20 April 1944, but Ro-45 was active after that date and apparently instead was sunk south of Truk Atoll on 30 April 1944 by the destroyers and . However, in the same vicinity as her supposed sinking of Ro-45, Seahorse sank the 5,244-ton cargo ship Akigawa Maru on 27 April 1944. On 29 April 1944, a U.S. Navy PB4Y-1 Liberator patrol bomber of Bombing Squadron 109 (VB-109) mistook Seahorse for a Japanese submarine and attacked her off Satawan southeast of Truk Atoll while she was on lifeguard duty, dropping two bombs as Seahorse crash-dived. Seahorse suffered a damaged antenna, but no other damage and no casualties. Seahorse departed her lifeguard station on 3 May to refuel at Milne Bay, New Guinea, and arrived at Brisbane, Australia, on 11 May. Fifth and sixth war patrols, June – October 1944 Seahorse put to sea for her fifth war patrol on 11 June 1944, patrolling between Formosa and Luzon. On the morning of 27 June, she sank the tanker, Medan Maru, and damaged two other enemy vessels. On 3 July, close to midnight, she spotted convoy No. 91 en route from Takao to Hong Kong consisting of four transport/cargo ships and two escorts (the Kuri and the Hatsukari). She torpedoed and sank the transport Nitto Maru and the cargo ship Gyoyu Maru (the ex-British Joan Moller) and then soon after midnight on the 4th, she expended the last of her torpedoes and sank