In early 1942, intelligence officers of the U.S. Navy predicted that there would be a Japanese attack in the North Pacific area, and naval codebreakers warned Dutch Harbor of the impending attack. On June 3, 1942, at 5:45 a.m., 20 Japanese planes from two aircraft carriers of the Imperial Japanese navy bombed Dutch Harbor in the "Battle of Dutch Harbor," targeting the radio station and the petroleum storage tanks, and continuing the fight a day later. It was the first aerial attack on the continental United States during World War II.