Japanese forces had occupied Attu and Kiska in the Aleutian Islands in June 1942, beginning the Aleutian Islands campaign, and by the spring of 1943 the Japanese garrisons in the two islands were becoming increasingly isolated. On 11 May 1943 U.S. forces landed on Attu, beginning the Battle of Attu. I-24 arrived at Kure on 20 May, and on 21 May, as the situation on Attu deteriorated, the Japanese Imperial General Headquarters decided to abandon the garrison on Attu and evacuate the isolated garrison on Kiska by submarine, with the evacuation to begin on 26 May 1943.