During the first week of June, 1942, Japanese aircraft bombed Dutch Harbor and Japanese troops occupied the islands of Attu and Kiska in Alaska's westernmost Aleutian Islands. This invasion marked the first time since the War of 1812 that an invading army had occupied American soil. A small naval party on Kiska and Aleut villagers on Attu were taken prisoner and transported to Japan. Concern that the war would come to other far western islands prompted the American government to evacuate residents from the Aleutian and Pribilof Islands and to destroy many of the islanders' homes, rather than let the invaders use them.

American aircraft and ships struggled with the Japanese forces and the treacherous Aleutian weather, first to isolate the invaders and then to destroy them. The Battle of the Commander Islands in March 1943, in which navy ships intercepted and turned back a Japanese flotilla seeking to bring more reinforcements, signified achievement of the first goal. For two and half weeks in May, 15,000 American troops clambered ashore at Attu and overcame stiff resistance from 2,400 Japanese defenders.

Kiska held 6,000 Japanese, so the American command assembled a force of nearly 100 ships and an invasion force of over 34,000 American and Canadian troops. But in late July the Japanese had managed a brilliant escape; while U.S. ships chased mysterious radar contacts 200 miles south of the island, eight enemy naval ships dashed to Kiska and carried away the emperor's soldiers. Not realizing this, however, the American and Canadian force attacked what proved to be a deserted island on August 15. Thus, the Japanese deserted their Alaskan gains two years before the end of the war.