When Japan launched its treacherous surprise attack on the United States Pacific Fleet at Pearl Harbor in Hawaii on 7 December 1941, and seized American island bases between Hawaii and the Philippines (Guam and Wake), one major aim was to facilitate capture of the Philippines without interference from the United States Navy. As starving American and Philippine troops fought a hopeless battle against invading Japanese troops between December 1941 and May 1942, any hope of reinforcement by the greatly weakened United States Pacific Fleet was negated by the Japanese Navy's control of the vast stretch of water between Hawaii and the Philippines. To appreciate the major contribution by General Douglas MacArthur to the American military disaster in the Philippines, see Battle of the Philippines.
Admiral King refused to accept the largely defensive role assigned to the US Navy in the Pacific War theatre by Winston Churchill and President Roosevelt. With the warships that were left to him after the treacherous Japanese attack on Pearl Harbor, he went on the offensive against Japan and almost certainly saved Australia and Hawaii from Japanese occupation in 1942.
At the time of Pearl Harbor, the warships of the United States Navy were mostly elderly relics dating back to the World War I era and earlier. This situation had been brought about by two decades of isolationism and neglect of the Navy by the US Congress and Administrations before that of President Franklin D. Roosevelt. An exception to this neglect of America's defences was the Pacific Fleet's force of four large fleet carriers. Each of these carriers was equal to any of Japan's six largest fleet carriers. The major difference between the American and Japanese carriers lay in the quality of the aircraft and the experience of the aircrews. The aircraft on the American carriers were either obsolete or nearing obsolescence. Most of the American aircrews lacked any combat experience, and many were under-trained. The Japanese naval airmen had been honing their combat skills in Japan's brutal war against China since 1937.