"Shōkaku" reached Kure, Japan, on 17 May, almost capsizing en route during a storm due to her battle damage. "Zuikaku" arrived at Kure on 21 May, having made a brief stop at Truk on 15 May. Acting on signals intelligence, the U.S. placed eight submarines along the projected route of the carriers' return paths to Japan, but the submarines were not able to make any attacks. Japan's Naval General Staff estimated that it would take two to three months to repair "Shōkaku" and replenish the carriers' air groups. Thus, both carriers would be unable to participate in Yamamoto's upcoming Midway operation. The two carriers rejoined the Combined Fleet on 14 July and were key participants in subsequent carrier battles against U.S. forces. The five "I"-class submarines supporting the "MO" operation were retasked to support an attack on Sydney Harbour three weeks later as part of a campaign to disrupt Allied supply lines. En route to Truk the submarine "I-28" was torpedoed on 17 May by the U.S. submarine and sank with all hands.