Navy General Staff develops a plan to isolate Australia from its American ally

With invasion of the Australian mainland blocked at this stage by the Japanese Army, planners in the First Section (Operations) at Navy General Staff set to work on a less ambitious plan that would effectively isolate Australia from its American ally. This plan had received the code reference "Operation FS", and it envisaged blocking American communication with Australia by extending Japan's southern defensive perimeter to Port Moresby in the Australian Territory of Papua, and then across the Pacific Ocean to the Fiji Islands. New Guinea, Fiji, and the islands between them, would be heavily fortified by Japan and equipped with forward air and naval bases. The waters between each island fortress in this chain would be guarded by the Japanese Navy.

Once completely isolated from the United States, Navy General Staff believed that Australia would be effectively defenceless and forced to submit to Japan. Admiral Nagano referred this plan to Imperial General Headquarters for consideration.

Admiral Isoroku Yamamoto, Commander in Chief of Japan's Combined Fleet. Yamamoto's stubborn insistence that the decisive battle between the Japanese Navy and the United States Navy had to take place at the remote Midway Atoll deprived his warships of protective cover from land-based aircraft and almost certainly cost him victory. It is very likely that Japan's defeat at the Battle of Midway saved Australia from invasion.

Imperial General headquarters approves the plan to isolate Australia

Imperial General Headquarters was very conscious of the urgent need to deny the United States access to Australia as a base for a counter-offensive. On 15 March 1942, Imperial General Headquarters approved Operation FS. The plan to isolate Australia was to be carried out under the overall direction of Vice Admiral Shigeyoshi Inouye at Rabaul.

The first Japanese targets would be Port Moresby on the southern coast of Australia's Territory of Papua and the island of Tulagi in the British Solomon Islands. Both targets were defended at this time by Australian military forces. The invasions of Port Moresby and Tulagi were fixed for April 1942, and the Japanese Army had agreed to the use of its elite South Seas Detachment which was then based in Rabaul. The large fleet aircraft carriers Shokaku and Zuikaku, formerly part of Vice Admiral Chuichi Nagumo's Pearl Harbor strike force, would steam from their base at Truk in the Caroline Islands to support these amphibious invasions and attack airfields in northern Queensland.

Following the rejection on 7 March of their plan for an invasion of Ceylon, staff officers of Japan's Combined Fleet turned their attention back to the central Pacific as a focus for a major offensive. They were alarmed at the ease with which American aircraft carriers were penetrating Japan's eastern and southern defensive perimeters and staging hit-and-run attacks on Japanese-occupied islands. The extensive damage inflicted by American carrier-launched aircraft on Japanese invasion forces at Lae and Salamaua on 10 March 1942 had already caused the invasions of Port Moresby and Tulagi to be postponed to May 1942.

To curb these hit-and-run attacks originating from Hawaii, Rear Admiral Ugaki proposed an "Eastern Operation" that would destroy the United States Pacific Fleet at Midway Atoll in the central Pacific and culminate in a Japanese invasion of Hawaii. Ugaki believed that a Japanese attack on America's Midway Atoll base in the central Pacific would be likely to draw the US Pacific Fleet to a decisive battle where it could be completely destroyed. At this stage, it was necessary for the plan to be submitted for approval to the Commander in Chief of the Combined Fleet, Admiral Isoroku Yamamoto.

Admiral Yamamoto, architect of Japan's infamous surprise attack on Pearl Harbor on 7 December 1941, was deeply concerned that the four aircraft carriers of the United States Pacific Fleet had escaped destruction by the Japanese Navy at Pearl Harbor. He pointed to the bold hit-and-run attacks by American aircraft carriers since 1 February 1942 on the Japanese-occupied Marshall and Gilbert Islands, Rabaul, Wake Island, Marcus Island, and mainland New Guinea, as proof of the American will to fight. Yamamoto's greatest fear was that the American aircraft carriers might be capable of breaching Japan's newly established defensive perimeter in the central Pacific Ocean and launching a retaliatory strike at Tokyo itself. If that occurred, the life of the emperor might be endangered.

Admiral Yamamoto demands that top priority be given to an Eastern Offensive

With this fear uppermost in his mind, Admiral Yamamoto approved Rear Admiral Ugaki's plan for an Eastern Offensive that would begin with total annihilation of the US Pacific Fleet at Midway Atoll in early June 1942 and culminate in an invasion of Hawaii in October 1942. Yamamoto directed that the plan for an Eastern Offensive be formally placed before Navy General Staff at a senior staff officer meeting on 2 April 1942.

Admiral Yamamoto had another compelling reason for supporting the Eastern Operation. He knew that Japan had to try to end the Pacific War before the United States could gather its formidable military strength. He hoped that total annihilation of the US Pacific Fleet at Midway Atoll would enable Japan to tighten a noose around Hawaii, and permit the fate of the five hundred thousand inhabitants of Hawaii to be used as a powerful bargaining chip to draw the United States into peace talks that would recognise Japan's claim to domination of the western Pacific including Australia.

We are indebted to the research of Dr J. J. Stephan, Professor of Japanese History at the University of Hawaii for disclosing the full scope of Admiral Yamamoto's Eastern Operation in his book "Hawaii under the Rising Sun" (1984) University of Hawaii Press. A detailed treatment of Eastern Operation can be found on this web-site at the Battle of Midway.

When presented to Navy General Staff on 2 April 1942, the Combined Fleet Eastern Operation plan received a cold reception. The senior staff officers of Navy General Staff had grave reservations about the Midway offensive which they viewed as a high risk gamble. Midway Atoll was an American airbase; it was a long way from any Japanese base; and it was relatively close to Pearl Harbor. Navy General Staff officers pointed out that their Operation FS plan to isolate Australia from the United States would be likely to draw the American Pacific Fleet to the defence of Australia in the South-West Pacific. If the decisive conflict between the Japanese Navy and the United States Navy took place near a major Japanese base, such as Rabaul in New Guinea, they argued that this would permit Japanese land-based aircraft to support the Japanese warships.

The Navy General Staff plan was tactically sound and clearly posed much less risk for a Japanese fleet in a major naval action. However, Yamamoto was stubborn and a gambler by nature. He threatened to resign if the decisive confrontation with the United States Navy did not take place at Midway. Faced with this threat, Navy General Staff reluctantly agreed to Yamamoto's plan. However, in return for that agreement, Navy General Staff insisted that an operation to capture and occupy islands in the Aleutian chain off Alaska must be undertaken at the same time as the Midway offensive. Yamamoto agreed, although he must have known that the Aleutian operation would produce a dangerous division of his available naval forces.

While agreeing that Yamamoto's Eastern Operation would have high priority, Navy General Staff was unwilling to permit resources already allocated to the plan to isolate Australia (Operation FS) to be reallocated to the Midway offensive.

Haggling over respective priorities of the Navy General Staff and Combined Fleet offensive plans continued until 18 April 1942, when American carrier-launched bombers struck Tokyo and other Japanese cities. See the Doolittle Raid. The bold American hit-and-run raid caused consternation in Japan and threw Japan's strategic planning and priorities off balance. After the Doolittle Raid, defence of Japan's home islands from attack by the United States Navy and isolation of Australia from the United States were both given the highest priority by Imperial General Headquarters. In the expectation that it would lead to total destruction of the United States Pacific Fleet, Imperial General Headquarters gave its approval for the Midway and Aleutian operations to be launched on 3 June 1942.

Japan had now committed itself to complex naval operations in the southern, central and northern Pacific in May and June 1942. Carried away by the euphoria produced by easy initial victories resulting from surprise attacks on British and American Pacific outposts, the Japanese military leadership had now made the fatal error of underrating American military capabilities and response. This arrogant belief in Japan's invincibility would save Australia, and ultimately lead to Japan's defeat.