was to embark four kaitens and their pilots. While conducting a trim test en route, however, she grazed a magnetic mine laid by a United States Army Air Forces B-29 Superfortress off Iwai Island on the northern side of the eastern entrance to Suō-nada in the Seto Inland Sea. The mine exploded, knocking out her diesel engines, destroying a number of her batteries, and causing a leak in a fuel tank on her starboard side. The damage forced her to return to Kure on one shaft, using her auxiliary engine. April–July 1945 After arriving at Kure on 1 April 1945, I-53 entered drydock for repairs. In addition, her forward deck gun was removed to make room for fittings on her forward deck allowing her to carry two more kaitens, giving her a maximum kaiten-carrying capability of six. Shipyard workers also equipped her with a snorkel and fitted underwater access tubes for all six of her kaitens so that their pilots could man them while she was submerged. With the work complete, she departed Kure on 9 July 1945 bound for Otsujima and carried out combat exercises during her voyage. She arrived at Otsujima on 13 July 1945. Third kaiten mission On 14 July 1945, I-53 was assigned to the Tamon Kaiten Group along with the submarines I-47, I-58, , , and . She embarked six kaitens and their pilots that morning and in the afternoon got underway for her operating area in waters about southeast of the southern tip of Formosa, which she reached on 22 July 1945. I-53 was operating submerged in the Philippine Sea northeast of Cape Engaño Lighthouse on 24 July 1945 when she sighted a U.S. Navy convoy consisting of the stores ship and six tank landing ships, carrying the United States Army′s 96th Infantry Division, which was being withdrawn from the Battle of Okinawa. Making , the convoy was proceeding toward the Philippines escorted by the destroyer escort , the patrol craft escort , and the submarine chasers , , , , , and . At about 12:00, Underhill picked up a sonar contact on I-53 and ordered PC-804 to conduct a depth-charge attack. Underhill then maneuvered to ram I-53, but I-53 dived and launched a kaiten at 14:25. Underhill dropped a pattern of 13 depth charges at 14:53. Meanwhile, the kaiten passed beneath PC-804. After it surfaced alongside Underhill, Underhill rammed the port side