Japanese officers in Aleutians; Wikimedia Commons
In 1942, U.S. Army units in Alaska totalled < 2300 men. Remote, sparsely-populated and infamous for harsh weather, the 1200 mile Aleutian Island chain appeared to have little military or strategic value.
However, perhaps to divert attention from imminent operations at Midway Island or to prevent invasion of homeland Japan via the Aleutians, Japanese airplanes attacked Dutch Harbor (site of two American military bases) on June 3-4.
On June 6-7, Japanese infantry invaded Kiska and Attu Islands and established garrisons. Kiska and Attu were the only actual U.S. soil Japan would occupy during the Pacific War.
Americans were shocked that Japanese troops had actually seized U.S. soil, and many feared it was the first step toward an attack against mainland Alaska or the Pacific Northwest.
Initially, their hands full with attacks on Pearl Harbor and the Philippines, American military planners considered action against the Japanese garrisons at Attu and Kiska a low priority.
In May 1943, U.S. troops retook Attu and three months later reclaimed Kiska. Aleutian military operations provided valuable experience that would prove useful in the subsequent “island-hopping” battles across the Pacific Ocean.
via Aleutian Islands Campaign – Wikipedia, the free encyclopedia.