While passing northwest of the Bonin Islands to take up her station, Bang encountered an enemy convoy on 9 September. Diving to make a periscope attack, she fired a salvo at two loaded freighters, both of which – Tokiwasan Maru and Shoryu Maru – disintegrated due to internal explosions triggered by the hits. The escorts evidently sighted Bang's periscope and torpedo wakes, because as she dove deep, the depth charges accurately drove her down beyond her test depth to 580 ft (180 m), where depth control almost disappeared.