Proposed Japanese invasion of Australia during World War II

In early 1942 elements of the Imperial Japanese Navy (IJN) proposed an invasion of Australia.

In Australia, the government, the military and the people were deeply alarmed after the fall of Singapore in February 1942 about the possibility of a Japanese invasion of Australia. Japan had the military capability, and Australia lacked defenses. Japan never actually planned an invasion, but the fear of one led Australia to form a close reliance on the United States to protect itself.

Meanwhile, in Tokyo the secret Navy proposal was opposed by the Japanese Army and Prime Minister Hideki Tojo, who regarded it as being unfeasible given Australia's geography and the strength of the Allied defences. Instead, the Japanese military adopted a strategy of isolating Australia from the United States by advancing through the South Pacific. This offensive was abandoned following the Battle of the Coral Sea and Battle of Midway in May and June 1942, and all subsequent Japanese operations in the vicinity of Australia were undertaken to slow the advance of Allied forces.

Japan's success in the early months of the Pacific War led elements of the Imperial Japanese Navy to propose invading Australia. In December 1941 the Navy proposed including an invasion of Northern Australia as one of Japan's 'stage two' war objectives after South-East Asia was conquered. This proposal was most strongly pushed by Captain Sadatoshi Tomioka, the head of the Navy General Staff's Planning section, on the grounds that the United States was likely to use Australia as a base to launch a counter-offensive in the South-West Pacific. The Navy headquarters argued that this invasion could be carried out by a small landing force as this area of Australia was lightly defended and isolated from Australia's main population centres. There was not universal support for this proposal within the Navy, however, and Isoroku Yamamoto, the commander of the Combined Fleet, consistently opposed it.

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