 In May , Shōkaku and Zuikaku were assigned to a mission to counterattack the American offensive in the Aleutian Islands , but this operation was cancelled after the Allied victory on Attu on 29 May 1943 . The sister ships were transferred to Truk in July . In response to the carrier raid on Tarawa on 18 September , the carriers and much of the fleet sortied for Eniwetok to search for the American forces before they returned to Truk on 23 September , having failed to locate them . The Japanese had intercepted some American radio traffic that suggested another attack on Wake Island , and on 17 October , Shōkaku and Zuikaku and the bulk of the 1st Fleet sailed for Eniwetok to be in a position to intercept any such attack , but no attack occurred and the fleet returned to Truk . At the beginning of November , the bulk of their air groups were transferred to Rabaul to bolster the defenses there , just in time to help defend the port against the Allied attack a few days later . They accomplished little there , for the loss of over half their number , before returning to Truk on the 13th . The sisters returned to Japan in December . 
