threat of Invading Australia to be found in Japanese documents, memoirs and minutes

The Japanese threat of invading Australia was genuine and imminent in early 1942 and is supported by a variety of documentation.

Photo: The bombing of Darwin.


An essay by Bob Wurth.



For the first few months of 1942 influential officers of the Imperial Japanese Navy were convinced that invading Australia was essential primarily to prevent the United States from using Australia as a base for future offensives, as in fact occurred.  

They pushed their plans to the limit of their considerable power and authority but we blocked by the Imperial Army during bitter debates, as found in Japanese documents.

Naval General Staff officers operating from the Navy ministry building in Tokyo (above) and staff officers from Combined Fleet, aboard Japan's flagships, both put forward senarios which included the invasion of part or all of Australia.

According to prominent Japanese war historian Hiromi Tanaka, an expert on Australian fighting in New Guinea, who teaches today at Japan’s National Defense Academy:  

“…there were so many high ranking officers, including those in the Navy General Staff, who were arguing about attacking Australia. Also in the Combined Fleet. Arguing about attacking and invading Australia. It wasn’t just the initiative of junior officers involved in this talk.”

Interviewed for the book in Tokyo, Tanaka’s words, and the accumulated Japanese evidence, dismisses claims by some historians in Australia that the proposed invasion of Australia was nothing but a ‘myth’.

Although the invasion of Australia was in the most part an Imperial Navy proposition, and was generally opposed as being too risky by the Imperial Army, there was at least one prominent general of the Imperial Army who was in favour of capturing parts of Australia in early 1942, when Japanese forces were rapidly expanding their empire.

The weight of evidence showing that invasion of Australia was seriously contemplated is there for the finding, especially in Japan. It is in official war histories, minutes of meetings between the Navy and the Army, in memoirs of Japanese officers, in official interviews conducted with participants, and in the writings of historians, both Japanese and Western.

[Below: Sydney Morning Herald February 16, 1942, abstract.]


There is not a shadow of doubt that Prime Minister John Curtin. the Press (see SMH left) and many of the Australian people genuinely believed in early 1942 that Australia was ripe for invasion. But how real were their fears?

Initially I broached the subject in research trips to Japan with considerable scepticism.  How could the Imperial Navy seriously contemplate an invasion of the Australian massive continent, so far from Japan at a time when Japanese forces were stretched with occupations over many parts of Asia and the Pacific?

It seemed a concept staggering in its complexity and a totally illogical one, given the size of Australia, the shortage of Japanese ships and fuel Australia’s its distance from the Japanese homeland. Hiromi Tanaka, a professor of history, has studied in depth the disaster of Imperial Army soldiers defeated and left for dead in New Guinea.

Tanaka insists that invasion of Australia was a deadly serious option in early 1942. “It is all there”, he says, “in Senshi sosho”, the 102-volume official war history series compiled over the years by the National Institute for Defense Studies (below).

The Institute is funded by the Government of Japan. The National Institute for Defense Studies (NIDS) has collected historical documents related to the Imperial Army and Navy, use in compiling the Japan's military history. Most of the documents were destroyed by the military at the surrender of Japan in World War II, and the rest were scattered. The papers that had survived were seized by the Allied Occupation Forces. They were returned to Japan in April 1958. Most of them are kept at the Military Archival Library of NIDS (below).

The many references to an invasion of Australia include this entry:

“Underlying this basic policy was support for the invasion of Australia, the main area from which to United States would launch counter-offensives against the Japanese.”

Professor Tanaka’s study of the Imperial Army in New Guinea has left him embittered about the Imperial Navy:

“You must understand that the Imperial Japanese Navy was such an irresponsible organisation; they never wanted to take responsibility.”

In reportage on the events of that fateful year, 1942, Australia’s greatest peril tells the story in detail of the bombing of Darwin and the midget submarine raid on Sydney Harbour. It should be noted that at no stage does 1942 attempt to portray these two events as being precursors to invasion, although invasion was being actively debated in Japan.

Those who would invade Australia

Officers on warship, including Yamamoto

There were many senior Imperial Navy officers in favour of an invasion of Australia at some stage during 1942. They included:

The commander in chief of the Combined Fleet, Admiral Isoroku Yamamoto; his chief of staff Admiral Matome Ugaki; the commander-in-chief of Japan’s second fleet, who led the southern invasion operations including the invasion of Malaya, Admiral Nobutake Kondo; the commander of the Japanese fourth fleet Admiral Shigeyoshi Inoue; the commander of the second carrier division, Admiral Tamon Yamaguchi;  the head of the bureau of naval affairs within Naval General Staff Admiral Takasumi Oka; and many powerful naval war planners, including the chief of the operations section of Naval General Staff, Baron captain (later rear admiral) Sadatoshi Tomioka.

General Tomoyuki Yamashita, who had captured Malaya including Singapore, wanted to capture Australia. There are indications in the early stages of the war that even the prime minister and war minister, General Hideki Tojo, could see benefits in invading Australia, a belief that runs counter to Tojo’s end of war denials about invading Australia.


Soon after the Japanese attack on Pearl Harbor and the initial invasions across the Pacific, the commander in chief, Admiral Isoroku Yamamoto, had chief of staff Admiral Matome Ugaki examine Japan’s ‘second stage’ offensives.  Initially Yamamoto insisted that Japan must follow through by aggressive action in all directions to keep the Americans off balance and allow Japan to expand the new perimeter until Washington sued for peace. But speed was of the essence.

Yamamoto told Ugaki, according to the war history series Senshi sosho, that he had three targets in mind: India, Australia and Hawaii. Of the three Yamamoto counted Hawaii as the most important, because of the strategic threat the Pacific base and its as yet untouched carrier fleet. The capture of Hawaii would allow Japan to take Midway in the mid-Pacific and Yamamoto knew that such an operation would draw out the US Pacific fleet for the Imperial fleet’s much anticipated “decisive battle”.

Australia was included in Yamamoto’s initial invasion plans because the commander-in-chief wanted a bold strategy which he called happo yabure, or “strike on all sides.” Among other considerations, Australia was seen as the obvious place where the United States would build up its forces to begin an eventual offensive against Japan.

But there were hurdles ahead if Yamamoto’s operation was to proceed. First the plan, at least technically, had to be signed off by the Naval General Staff, who were traditionally conservative about the use of Japan’s precious capital ships. More importantly, any such proposals needed to be accepted by the Army, and that was a tougher nut to crack, before the emperor could consider approval of a final plan.

According to his diary, Ugaki mused aboard Yamamoto’s flagship:

Admiral Ugaki


“Should we capture India after Burma, Hawaii, or perhaps Australia?”

After much personal study, Ugaki, an experienced strategist, in late January and early February came down favour capturing Australia’s north, among other landings. Ugaki’s operational planners in Combined Fleet embraced invading northern Australia, along with other strategic points. They submitted a plan to Navy General Staff listing the following priorities:

“One, invade Ceylon at the end of May/June; establish contact with the German forces; mission accomplished, Combined Fleet will turn toward the east.

“Two, Port Darwin must be taken.

“Three, Fiji and Samoa need not be taken, only destroyed.

“Four, we should like to take Hawaii, if possible.”

The proposals would provoke more debate. Naval General Staff soon agreed with the aims of the seaborne planners in Yamamoto’s Combined Fleet. They had gained considerable influence and flaunted it after the success of the Pearl Harbor attack.

On 6 February, Naval General Staff in a meeting with their Army counterparts in Tokyo put up a plan for invading eastern Australia at the same time as invasions of Fiji, Samoa and New Caledonia. The Australia proposal was pushed by one of the firebrands of Naval General Staff, Captain Shingo Ishikawa, who had long argued that Japan had a god-given right to conquest in the South Seas:

“There will be no security for the Greater East Asia Co-Prosperity Sphere unless we make Australia the main target in stage two of our basic war plan and annihilate it as a base for the American counter offensive.”

Some radical middle-ranking Imperial Navy officers had extraordinary power and influence, and war planning was more often occurred ‘from the bottom up’ where the most senior officers were presented with plans from their subordinates for major offensives.

Sadatoshi Tomioka and his Naval  General Staff planners. Tomioka, seated left


The Imperial Army could only disagree with invasion plans for Australia, vigorously pointing out the need to plan for war against Russia. “Blinded by victory our onslaught in the Pacific is getting dangerous. We must realise our limits in the Pacific offensive”, the Army operations section chief, Major-General Shinichi Tanaka wrote of the Australia debate in his diary.

After the war Tanaka would tell US interrogators:

“The Navy wanted to take Port Darwin in northern Australia. They insisted that we take it because the American Navy would use it as a base from which to attack Moresby and the Bismarcks … I absolutely refused to agree to the operation.”

‘We can take Australia’

The head of the operations bureau at Naval General Staff Baron Sadatoshi Tomioka, who had links to the Imperial family and whose father had been an admiral, insisted that after Hawaii had been occupied, the invasion of Australia should quickly occur:

“No matter what happens, in order to win we simply cannot allow the enemy to use Australia. If the enemy is not able to prepare themselves yet, then we can take Australia.”

The conclusion was that the Imperial Navy would first take tiny Midway, and once that had been done, it would turn attention back to isolating Australia from America.

Sadatoshi Tomioka with sword


Research reveals that the worldly, courteous and reportedly intelligent war planner, Sadatoshi Tomioka, (pictured) a captain in 1942 but soon to be promoted to rear admiral, had become one of the leading proponents of invading Australia.

Tomioka was responsible for the assessment and development of naval war plans. He was considered a highly gifted officer. Initially he strongly opposed rash naval action, including the attack on Pearl Harbor. But with Japan’s seemingly endless victories in early 1942, he became a convert. He thought invading Australia was essential and conducted a strong campaign to that end:

“The enemy had to be beaten and victory won. In order to win, the enemy had to be denied the use of Australia as a base, no matter what. As long as the enemy had no foothold there, Australia could be taken.”

On 14 February - one day before the fall of Singapore - army and navy chiefs confronted each other again in Tokyo. A Navy ministry official suggested that because the war situation was no more than expected, was it not a good chance to make a clean sweep of Australia’s forward bases?

Colonel Etsuo Kotani: “It cannot be said that the situation has improved …. It is too difficult. We have no reserves.” Baron Tomioka was adamant and desperate:

“But if we take Australia now, we can bring about the defeat of Great Britain. With only a token force we can reach our aim!”

Colonel Takushiro Hattori

In another heated debate over the issue, the Army’s chief of operations at General Staff HQ, Colonel Takushiro Hattori told Tomioka he would never condone the Navy’s plans:

“From early in 1942, the plans for the invasion of Australia were under consideration by a faction in the Navy. However, this was clearly a reckless operation which would exceed the war strength of Japan….”

Off Hashirajima on the Inland Sea, Combined Fleet chief of staff Admiral Ugaki was prepared to accept the destruction of Australia’s northern port by a massive aerial bombardment of Darwin but did he abandon the idea of an invasion of Australia. Simply, the priorities would be rearranged, which was something to be expected in war, and the invasion of Australia could be delayed a little.

Darwin was devastated by carrier-based aircraft on 19 February 1942. The raids killed 243 people and wounded more than 400, although these casualty figures at the time were significantly downplayed.

Prime Minister John Curtin announced that 93 Japanese bombers had taken part in two raids and four enemy planes had been brought down.

The Kondo plan

Admiral Kondo

A series of senior naval officers wanted to invade Australia. Admiral Nobutake Kondo had been chief of staff of the Combined Fleet, chief of the Naval General Staff operations division and deputy chief of the General Staff. Kondo was no radical. But the Japanese were touched by ‘victory fever’. Kondo and his staff officers aboard the flagship Atago prepared a proposal for consideration by Yamamoto.

Kondo believed the fatal blow to the enemy would be the fall of the British Empire, which he judged to be the weakest point of the Allied powers. Thus he saw Japan as having two planning options; one was an operation to take India and the other, an operation to capture Australia.

Kondo preferred the operation against Australia because the India operation required Germany to penetrate Iraq and Iran, cutting oil resources to the British Empire:  

“The Australia operation, on the contrary, could be regarded as part of our main operation against America and also would have a rich chance of taking hold of American task forces.”

Another Imperial Navy senior officer considered by his peers and historians as a moderate and certainly not a radical was an advocate for invading Australia.

Vice admiral Shigeyoshi Inoue was the commander of the Japanese Fourth Fleet, based at Truk island headquarters in the Caroline Islands. Inoue’s staff officers aboard the cruiser Kashima at Truk, including his chief of staff Captain, later Rear Admiral, Shikazo Yano, worked on operation offensives that dove-tailed with the plans of Sadatoshi Tomioka in Naval General Staff.

These called for the Japanese expansion in the Solomons-New Guinea area, as the necessary first steps required for landings on the Australian mainland. Inoue and his planners also recognised the danger that the Allies would pour unlimited amounts of men and material into Australia to turn it into an offensive base against Japan’s southern perimeter.

The Yamaguchi plan



The ‘The Yamaguchi plan’ came to light during table manoeuvres aboard Yamamoto’s flagship, the super battleship Yamato, anchored off Hashirajima on the Inland Sea. The plan came from a close confidant of the commander-in-chief Isoroku Yamamoto, Rear Admiral Tamon Yamaguchi, the commander of the Second Carrier Division including the carriers Hiryu and Soryu.

Between 20 and 23 February Yamaguchi was aboard the Yamato at Hashirajima taking part in mock exercises for an invasion of Ceylon. He distributed to naval officers copies of a blueprint invasion plan that he had drawn up. It included a proposal for a crash naval and air construction program to allow Japan to participate in widespread invasions across the Indian and Pacific oceans starting from May 1942.

He proposed an invasion of Ceylon in May. During June and July 1942 landings would be made on Fiji, Samoa, New Caledonia, New Zealand and northern Australia.

Midway, Johnston and Palmyra islands would be occupied in November and December while Hawaii would be invaded and occupied from December 1942 or January 1943. The ‘Yamaguchi plan’ caused much discussion but when the army got wind of some of it, there was immediate opposition to the more significant undertakings, including the invasion of Hawaii.

More to the point, Yamamoto was becoming interested in a new plan -taking the two small islands that made up what we call Midway in the mid-Pacific, first as a precursor to an invasion of Hawaii, a plan, if successful, would have meant follow-up invasions of Australia, New Zealand and adjacent islands.

Yamashita: 'simply to subdue Australia


General Tomoyuki Yamashita, the ‘Tiger of Malaya’ who had so quickly captured Singapore, was imprisoned near Manila, awaiting trial as a war criminal in 1945, when he spoke of his wartime plans for invading Australia, to quote author John Deane Potter: 

General Yamashita


“He said that after he had taken Singapore, he wanted to discuss with Tojo a plan for the invasion of Australia …Tojo turned down the plan, making the excuse of lengthened supply lines, which would be precarious and open to enemy attack…

“Yamashita’s plan to conquer Australia was practically identical with his successful campaign in Malaya. He intended to land on each side of the major Australian cities and cut them off, first making a series of dummy landings to draw off the pitifully few Australian troops.

“‘With even Sydney and Brisbane in my hands, it would have been comparatively simply to subdue Australia. I would never visualise occupying it entirely. It was too large. With its coastline, anyone can always land there exactly as he wants’...”   Pictured: General Tomoyuki Yamashita.


Oka: ‘actively move our forces to Australia’


The influential hard-liner, Admiral Takasumi Oka, head of the bureau of naval affairs within Naval General Staff in Tokyo, vehemently disagreed with Army plans to maintain a strictly defensive stance:

“[We] need to actively move our forces to Australia and Hawaii, annihilate our enemies’ marine military force, and decimate our enemies’ bases for counterattack … it is vital that we procure resources within the co-prosperity sphere and ensure that they are not taken by our enemies…”

Bitter debate continued about Australia between the Army and the Navy. The Navy eventually appeared to accept the Army’s reasoning, but it merely deferred its desire to invade Australia. However, as Hattori noted in one of his memoirs, “…the Navy did not abandon its stand in subsequent war guidance, and attempted to maintain the offensives in its war operations.”

The Army’s chief of staff General Hajime Sugiyama, who took minutes of vital planning meetings in March 1942, summarised the conflicting arguments:

“Put simply, the Navy argued for an aggressive offensive that included attacking Australia, whereas the Army outright opposed attacking Australia, stating that the focus ought to be on firmly establishing the situation so that Japan will be unbeatable in the long-term.”

General Sugiyama when referring to ‘attacking Australia’ was in fact speaking about invasion because at the time of writing, Darwin was already being bombed from the air.


Tojo: ‘…but also Australia’

General Hideki Tojo

Prince Naruhiko Higashikuni

Pic tures: Tojo (top), Higashikuni (bottom.)

After the war, awaiting trial for war crimes for which he would be hanged, ex-Prime Minister Hideki Tojo said Japan never had plans to invade Australia. This quote has been used repeatedly in Australia in efforts to prove that Australia was never under the threat of invasion.

However, Prince Naruhiko Higashikuni, an uncle to the Empress Nagako, tells a much different story in his memoirs. In December 1941 Higashikuni was commander of Defense Command and a member of the Supreme War Council.

In his diary, Higashikuni said he wanted Japan to quit while still ahead and occupying a vast new empire. He told Tojo after the initial successes:

“I think Singapore will fall soon … Japan should … start peace overtures with Britain and the United States. We must end this war without further delay.”

According to Higashikuni, Tojo was defiant, replying:

“I think we will have few problems occupying not only Java and Sumatra but also Australia if things go on like this. We shouldn’t think about peace at this time.”

Temporary invasion of Darwin

The critical debate about the invasion of Australia took place between late January and mid March 1942. During this period the Imperial army and navy were in constant disagreement. In time, with General Tojo’s support, the Japanese Imperial Army gained the upper hand in the invasion debate about Australia in Tokyo, although the Navy refused to abandon the idea, considering it for some time merely to be shelved.

But as a compromise in the debate, the Imperial Army agreed to more easily achievable and realistic goals, including the invasion of the Australian base of Port Moresby.  Prime Minister Tojo, General Sugiyama and Admiral Nagano put a compromise solution to Emperor Hirohito on 13 March.

The Army allowed inclusion in the text of a ‘temporary invasion of Darwin’ as a future option to demonstrate ‘positive warfare’. But the ‘temporary invasion of Darwin’ proposal had so many tough Army conditions attached, including the need for major victories elsewhere, that of itself it would not lead to invasion of Australia’s north.

Japan’s devastating losses in the Battle of Midway significantly helped to secure Australia’s safety, but the threat had been very real.

-Bob Wurth, detail edited from 1942, Australia’s greatest peril.





Admiral Yamamoto.

Sunday Telegraph, December 7, 1941, one of


Sunday Telegraph, December 7, 1941, one of the few newspapers published in Australia that day.


New York Times February 17, 1942.

Picture: Dept. of Navy, Tokyo, c. late 1930s.