In World War II, the only U.S. soil to be captured by the Japanese Imperial Army was the so-called Outer Aleutians. Located approximately equidistant between Los Angeles and Tokyo, the unopposed seizure in June, 1942, of the barren and virtually unpopulated islands of Kiska and Attu in the Bering Sea was the only Japanese success resulting from the otherwise disastrous Battle of Midway.
The Japanese forces committed to this diversionary operation were barely adequate -- the Imperial Navy's Fifth Fleet, including two light carriers and a seaplane carrier along with the Imperial Army's Northern Sea Detachment (Hokkai) of little more than a single infantry regiment, augmented with a separate force of about 550 special naval landing troops.
This force managed to capture two U.S. missionaries and 10 unarmed weather personnel, and due to the bad weather it took the Americans a week to discover that Japanese forces were on Kiska and Attu, causing American military planners to rush troop reinforcements to Alaska to counter whatever the Japanese may have had in mind.