Despite Australian fears, the Japanese never intended to invade the Australian mainland. While an invasion was considered by the Japanese Imperial General Headquarters in February 1942, it was judged to be beyond the Japanese military's capabilities and no planning or other preparations were undertaken. Instead, in March 1942 the Japanese military adopted a strategy of isolating Australia from the United States by capturing Port Moresby in New Guinea and the Solomon Islands, Fiji, Samoa and New Caledonia. Yet this plan was frustrated by the Japanese defeat in the Battle of the Coral Sea and was postponed indefinitely after the Battle of Midway. While these battles ended the threat to Australia, the Australian government continued to warn that an invasion was possible until mid-1943. A series of Japanese air raids against northern Australia occurred during 1942 and 1943, and while the main defence was provided by RAAF and Allied fighters, a number of Australian Army anti-aircraft batteries were also involved in dealing with this threat.