The Japanese were planning to invade Australia or compel its surrender in 1942

Japan's top admirals and generals appreciated at the beginning of 1942 that Australia represented a serious threat to Japan as an ally of the United States. They also appreciated the need to isolate Australia from the United States, and compel its submission to Japan. It was only in the means deemed necessary to secure Australia's submission to Japan that there was a difference of approach.

The admirals of Japan's Navy General Staff and Navy Ministry wanted to invade key areas of northern Australia in early 1942 to isolate Australia and neutralise it, but they were denied troops at that stage by Japan's generals who considered that their army resources had already been overextended.

The generals of the Army General Staff, and the Prime Minister of Japan, General Hideki Tojo, did not see a need to commit massive troop resources to the conquest of Australia in the early months of 1942. The easy capture of Rabaul and the initial bombing of Darwin had shown the Japanese that Australia had little with which to defend itself from invasion in early 1942. The generals were confident that Australia could be bullied into submission to Japan by isolating it completely from the United States and by applying intense psychological pressure. In January, February, and May 1942, General Tojo had publicly demanded Australia's surrender. It is difficult to see how an Australian surrender to Japan, of the kind contemplated by the generals, could be meaningful without some form of Japanese occupation that would exclude access to Australia by the United States. The Japanese generals did not rule out their support for an invasion by force if Australia did not surrender as they expected.

It follows, in my view, that the statement on the Veterans' Affairs web-site "The Japanese had no plans to invade Australia during the Second World War.." is incorrect and misleading. It also follows, in my view, that the Australian War Memorial's Dr Peter Stanley was incorrect and less than fair to Prime Minister John Curtin when he told The Weekend Australian newspaper that the threat of Japanese invasion in 1942 was "a furphy", and that it was exploited by Prime Minister John Curtin to "garner votes for the Labor Party" even though Curtin knew there was no threat.

The Battle of Midway saves Australia from Japanese invasion

If Japan had won the Battle of Midway in June 1942, and achieved its aim of destroying the United States Pacific Fleet, the history of Imperial Japan's defensive planning suggests that a high priority would then have been given to blockading Hawaii, and capturing the Australian mainland and the string of islands between Australia and Hawaii before the United States could rebuild its Pacific Fleet. This could not happen before 1943. With no powerful American ally to defend it, Australia would have been unable to resist a Japanese invasion in the second half of 1942. Australia, Hawaii, and the islands between them, would then become part of Japan's eastern and southern defensive perimeters. This approach would place the unbroken vastness of the eastern Pacific Ocean between Japan's extended defensive perimeters and the west coast of the United States. The task of recovering its lost Pacific territories, including Hawaii, would be an intimidating prospect in 1943 even for a country with the industrial strength of the United States. Japan's Admiral Yamamoto hoped that the United States might baulk at the likely high cost in lives and national treasure of such an enterprise, especially if the lives of half a million inhabitants of Hawaii were also at stake, and might be persuaded to accept a peace settlement that accepted Japanese domination of the western Pacific Ocean, including Australia.

Fortunately for Australia's survival, developments in the Pacific arena between March and June 1942 caused the destruction of the United States Pacific Fleet to become one of Japan's highest strategic priorities, and Admiral Yamamoto's status ensured that he would decide where that destruction would take place.

Japan's Navy General Staff were confident that the US Pacific Fleet would come to the defence of Australia if the continent was threatened by invasion or by complete isolation from the United States. The Navy General Staff wanted the decisive battle between the Japanese and American navies to take place close to Australia and within flying range of a major Japanese base, such as Rabaul. This scenario would have given the Japanese Navy an enormous advantage, and placed Australia in great peril. It is difficult to understand why Admiral Yamamoto obstinately insisted on fighting the most important battle of the Pacific War at the remote Midway Atoll in the central Pacific where his warships would be far beyond the protective cover of Japanese land-based aircraft. However, Yamamoto's foolishness and the crushing defeat inflicted on his Combined Fleet at the Battle of Midway would deny Japan the naval capability to invade the Australian mainland or isolate Australia from its American ally.