to 24 March, she was on lifeguard duty to the southeast of the Nanpō Islands. On 25 March, she moved into that chain and, on 28 March she closed the Kyūshū coast off Cape Toi. The next day, lifeguard duty took her on a high speed run south to the Osumi Islands, where sea planes picked up the downed pilots as she arrived. A short while later, however, a third plane circled, then ditched eight miles off. Sea Dog picked up the pilot, submerged, and headed back to the Kyūshū coast. At 1903, as she was making preparations to surface, she sighted an enemy I-boat which had just surfaced. Sea Dog took the offensive and fired on the submarine but not fast enough. The torpedoes missed, and the I-boat escaped.Sea Dog remained off the Kyūshū coast for another day; then moved north to lifeguard duty south of Sagami Wan. Although assigned to cover both sides of the Izu Shoto, resulting in much of her time being spent on high speed runs south around Mikura-jima with no rescues being made at the end of the runs, potential target opportunities increased. On 2 April, she sighted and fired on a small minelayer. All torpedoes missed. On 16 April, she sank a medium-sized cargo ship, Toko Maru, between Hachijo Jima and Mikura-jima. A typhoon then interrupted both hunting and rescue operations; and, on 23 April, she headed for Guam. Fourth War Patrol Refit took Sea Dog into May, when preparations were made for her last foray into Japanese home waters. Additional duties during the patrol included those of flagship for the nine-submarine Japan Sea Patrol Pack (TC 17.21). On 27 May, she departed Guam with the other two submarines of her immediate pack, and . Later that day, the ships separated to proceed independently, planning to rendezvous on 4 June. On 28 May, one of Sea Dog's crew became seriously ill and was diagnosed as a possible pneumonia case. On 29 May, the submarine rendezvoused with and, after transferring the patient to that destroyer, continued on to the Sea of Japan. On arrival, Sea Dog reconnoitered the approaches to western Honshū ports to locate minefields; then took up station off the east coast of Sado Island. At 2000 on 9 June, she sank her first target of the patrol, the small cargo ship, Sagawa Maru. Twenty-three minutes later, she made her second contact;