The South Pacific air ferry route was initially established in the 1920s to ferry United States Army Air Service aircraft to the Philippines. As the Japanese threat in the Far East increased in 1940, General Douglas MacArthur planned that in the event of war, the United States Army Air Corps would play a major role in defending the Philippines. The reinforcement by the Air Corps of forces in the Philippines, and later Allied forces in Australia, became the basis for developing the South Pacific air ferry route used during World War II.