During World War II, in June, 1942, the Japanese seized the Aleutian Islands of Attu and Kiska. These islands are part of the chain of Aleutian Islands, located off the tip of Alaska, and provided the Japanese with a base from which to limit Allied air and sea operations in the North Pacific. In an effort to recapture the islands, the United States established airfields on Adak and Amchitka Islands in August, 1942. Plans were made in the spring of 1943 to recapture Kiska and Attu. It was eventually decided to bypass Kiska, and American and Canadian forces landed on Attu on May 11, 1943. Air and naval units supported the operation. The Japanese on Attu defended their position intensely, and the fighting continued until May 30, when Japan announced the loss of the island.

On August 15, 1943, a powerful Allied amphibious force, including a U.S. infantry division and elements of the Royal Canadian Army, assaulted the island of Kiska, where the Japanese had developed their largest base. To the surprise of the Allies, they found that the Japanese, under cover of heavy summer fog, had secretly evacuated the island. In August, 1943, the island was declared secure, thus ending the Aleutian Islands Campaign. During 1944 the Canadians left and U.S. Army presence in Alaska dropped from a high of 144,000 to 63,000 personnel. Although interest in the Alaskan theater waned, it was in the Aleutians that the Allies won their first theater-wide victory in World War II, ending Japan's only campaign in the Western Hemisphere.