The Department of Defence was looking for military airfield sites in northern Australia at the time, and almost immediately Townsville Airport was planned for expansion as a Royal Australian Air Force (RAAF) base for three fighter squadrons. The plans were scaled back to one squadron, and RAAF Base Townsville was built alongside the civil airport in early 1940. In October 1940, Number 24 Squadron, flying CAC Wirraways, became the first operational unit to occupy the base. A year later the airfield was greatly expanded to take United States Army Air Corps bombers and transport aircraft reinforcing the Philippines. All three runways were sealed, and the south-east runway was extended to to take the heavier aircraft. The work was nearly finished in early December 1941 when the Pacific War began.