On 6 June "Harder" entered the heavily patrolled Sibutu Passage between Tawi-Tawi and North Borneo and encountered a convoy of three tankers and two destroyers. She gave chase on the surface but was illuminated by the moon. As one of the destroyers turned to attack, "Harder" submerged, turned her stern to the charging destroyer, and fired three torpedoes at range of . Two struck "Minazuki" and exploded; the destroyer sank within five minutes. After attacking the second escort without success, "Harder" was held down by a depth charge attack while the convoy escaped.