Heading the same attack group, "Flasher" now commanded by Lieutenant Commander G. W. Grider, sailed on her fifth war patrol 15 November 1944, bound for Cam Ranh Bay. On 4 December one of her companions reported a tanker convoy, and "Flasher" set a converging course. As she made her approach in a heavy downpour, a destroyer suddenly loomed up before her, and "Flasher" launched her first spread of torpedoes at this escort. The destroyer (Kishinami) was stopped by two hits, and began listing and smoking heavily. "Flasher" got a spread of torpedoes away at a tanker before she was forced deep by a second destroyer, which dropped 16 depth charges. Rising to periscope depth, "Flasher" located the tanker burning and covered by yet a third destroyer. Speedily reloading, she prepared to sink the destroyer and finish off the tanker, and though almost blinded by rainsqualls, she did so with a salvo of four torpedoes, two of which hit the destroyer (Iwanami), and two of which passed beneath her, as planned, to hit the tanker (Hakko Maru 10,022 tons). Once more, counter-attack forced "Flasher" down, and when she surfaced she found no trace of the two damaged destroyers. The tanker, blazing away, was still guarded by three escorts until abandoned at sunset, when "Flasher" sank her with one torpedo. The two destroyers, both found after the war to have been sunk, were "Kishinami" and "Iwanami".