With the bombing of Pearl Harbor on 7 December 1941 the Americans had been brought into the war. The Japanese advance south was swift and successful, taking the Philippines, Hong Kong, Malaya and Rabaul in January and Singapore in February 1942. In the same month Darwin was bombed. Faced with the threat of invasion, (Townsville was put on invasion alert on 1 May 1942), the Australian and American Governments began to develop a major military base in the Townsville region. As a result, the air base at Townsville was further expanded as thousands of troops descended upon the city. Further air fields were developed west of Garbutt, and further west again at Charters Towers and Macrossan. The sphere of influence of the Townsville base was much wider than before. Townsville became the base for North East Area Command, with its major responsibility the protecting of sea lanes to the north to Port Moresby.