Hake's fourth war patrol was spent in the South China Sea near Singapore, following departure from Fremantle 18 March 1944. She encountered her first target 27 March off southwest Borneo, and it was a submariner's dream: an unescorted tanker. Two torpedoes sent the ship, Yamamizu Maru, to the bottom. After an attack on convoy Hi-55 during the night of 1 April in which Hake damaged several ships, she battled escorts and searched for more transports until 30 April, when she arrived at Fremantle.
