On 17 October, she arrived off Paramushiro and, that evening, she took up station off the southeast coast of the island to patrol the entrances to Musashi Wan and Onekotan Strait. On the morning of 18 October, she sighted two ships at anchor in Musashi Wan, and, after a periscope check disclosed no other ships in the area, she began working her way to an attack position west or southwest of the targets. Moving slowly, with short and infrequent periscope exposures, through the calm and poorly charted bay, she went up for a final check at 10:23. While looking, she struck an uncharted sand bar. The S-boat, her tubes ready for firing, angled up 10 degrees. Her depth gauge showed . During the next few seconds she slid over the bar, apparently showing periscope shears, bow, and, possibly, the whole bridge structure; then, over the bar, she took a down angle at high speed. At 10:25, she fired. Two torpedoes set at six feet, were sent against each of the targets. On firing the fourth and final "fish", she changed course and maneuvered at high speed toward the open sea. Two explosions were heard as she cleared the immediate area. At 10:45, she came to periscope depth to observe the damage.