On 1 December 1943, "Tsugaru" was reassigned to the Third Southern Expeditionary Fleet. On 24 March 1944, she deployed from Palau to mine the Balabac Strait in the Philippines, after which she was stationed at Balikpapan in Borneo. One of the mines from this mission is credited with sinking the , in July 1944. On 31 May, "Tsugaru" was assigned to “Operation KON” (the Relief of Biak), transporting reinforcements from Zamboanga on Mindanao in an effort to counter the American landings. On 21 June, after departing Sorong, New Guinea for Halmahera Island, "Tsugaru" was torpedoed by the Royal Dutch Navy submarine "K-XIV", which caused severe damage. After temporary repairs, she attempted to reach Manila, but was sighted on 29 June near Biak by , which fired a full spread of six torpedoes. Two hit "Tsugaru", which sank at position less than 25 minutes later with loss of most of her crew, including her CO, Captain Nakatsu.