Operation FS - The Japanese plan to isolate Australia from the United States and force its surrender to Japan

The Imperial Japanese Navy had operational responsibility for the Pacific Ocean during World War II, including Australia and its two territories on the island of New Guinea. Japan's naval planners appreciated that the vastness of the Pacific would hamper an effective American counter-offensive in response to Pearl Harbor unless the Americans could use Australia as a base and springboard for an assault on the islands of Japan's southern defensive perimeter. The Japanese admirals appreciated that, with Australia providing a friendly and supportive base, the Americans would be able to use the islands of the South-West Pacific as stepping stones to recover the Philippines and threaten Japan's home islands.

The doomed USS Lexington at the Battle of the Coral Sea. As fires rage out of control, the crew
of the American aircraft carrier have been ordered to abandon their well loved "Lady Lex".

To counter the perceived threat from Australia as an American ally, the admirals of Japan's Navy General Staff and Navy Ministry wanted to invade key areas of the northern Australian mainland in early 1942 to isolate Australia from American and British aid. To invade Australia, the Japanese Navy would require troops from the Japanese Army.

The generals of the Japanese Army General Staff, and the Prime Minister of Japan, General Hideki Tojo, appreciated that Australia posed a serious threat to Japan while it remained an ally of the United States. However, when the Japanese Navy requested troops for an invasion of Australia at a meeting of the Army and Navy Sections of Japan's Imperial General Headquarters on 4 March 1942, the generals refused. The Japanese generals did not see a need to commit massive troop and logistical resources to the conquest of the Australian mainland in the early months of 1942. The easy capture of Rabaul on 23 January 1942 and the first bombings of Darwin on 19 February 1942 had convinced the Japanese Army that Australia had little with which to defend itself from invasion. It was the sheer size of Australia that the generals saw as an immediate problem. The generals felt that their army resources had already been heavily overextended by Japan's rapid and massive territorial conquests, and that the Imperial Army needed time to consolidate its territorial gains.The Japanese Army was confident that Australia could be bullied into submission to Japan by isolating it completely from the United States and by applying intense psychological pressure.

By early March 1942, the Japanese Navy and Army had agreed that severing Australia's lifeline to the United States and bullying Australia into surrender to Japan were more important objectives than the limited invasion of Australia's northern coast that the Navy had earlier proposed. At the Imperial General Headquarters Liaison Conference on 7 March 1942, the Navy General Staff and Navy Ministry agreed to their limited invasion proposal being deferred in favour of the Army plan to sever Australia's lifeline to the United States and then press for Australia's total surrender to Japan. It is important to note that the Japanese generals did not rule out their support for an invasion by force if Australia did not surrender as they expected when the Japanese noose was tightened.

In public addresses to the Diet (Japanese parliament) on 21 January 1942, and on the occasion of the fall of Singapore (15 February 1942), Japan's Prime Minister, General Hideki Tojo, called on Australia to surrender to Japan. General Tojo suggested that Japan would be merciful to Australia if this happened. Tojo would repeat this demand for Australia's surrender in the Japanese parliament on 28 May 1942. To demonstrate Australia's vulnerability, Japanese midget submarines penetrated Sydney Harbour on 31 May 1942 and torpedoed the Royal Australian Navy depot ship Kuttabul, killing twenty-one sailors. Although Tojo suggested that Australia would be treated with leniency if it surrendered to Japan, I find it difficult to see how an Australian surrender to Japan could serve Japan's purposes without some form of Japanese occupation that would exclude access to Australia by the United States.

Although Tojo suggested that Australia would be treated with leniency if it surrendered to Japan, I find it difficult to see how an Australian surrender to Japan could serve Japan's purposes without some form of Japanese occupation that would exclude access to Australia by the United States.

On 15 March 1942, with Emperor Hirohito's approval, Japan's military high command formally resolved to extend Japan's southern defensive perimeter from Port Moresby in the Australian Territory of Papua to Fiji and Samoa for the purpose of isolating Australia from the United States. This plan was given the Japanese code reference "Operation FS", and was to be carried out as a matter of high strategic priority under the overall direction of Vice Admiral Shigeyoshi Inouye at Rabaul. Once completely isolated from the United States, the Japanese military leaders believed that Australia could be "neutralised" and bullied into surrender to Japan by threat of a military onslaught against major cities on the Australian mainland.

In Australia, Tojo's demands for surrender fell on deaf ears.

Operation MO - The Japanese plan to capture Port Moresby and Tulagi

The initial phase of Operation FS would involve the capture of Port Moresby and the island of Tulagi in the southern Solomon Islands. Both were garrisoned by Australian troops. The Japanese gave this initial phase the code reference "Operation MO".

The capture of Port Moresby was of vital importance to Japan's military leaders in 1942. Port Moresby was situated on the southern coast of the Australian Territory of Papua and separated from the Australian mainland by a 500 kilometre (310 mile) stretch of the Coral Sea. Its capture would enable the Japanese to block the eastern sea approaches to Darwin and deny the Allies a forward base from which to launch air attacks on Japan's newly acquired military bases in the Australian Territory of New Guinea. These bases included Rabaul, Lae, Salamaua and Kavieng. With the whole of the island of New Guinea and the Solomon Islands under Japanese control, Japan could establish forward air and naval bases on these territories from which it could strike deeply into the Australian mainland and sever the vital lines of communication between the United States and Australia. Port Moresby would also provide Japan with a springboard for an invasion of the Australian mainland when that became feasible.

Although Operation MO was intended to take place in April 1942, carrier-launched aircraft from USS Yorktown and USS Lexington had crossed the Owen Stanley Range on 10 March 1942 and destroyed and damaged Japanese warships and troop transports at Lae and Salamaua on the north coast of New Guinea. The troop transports were to have been used in Operation MO, and the successful American air strike forced a one month postponement of Operation MO to enable the lost and damaged transports to be replaced and deployment of Japanese aircraft carriers to protect the Port Moresby and Tulagi landings.

Admiral Yamamoto puts forward an alternative plan and calls for deferral of aspects of Operation FS

As noted earlier, on 15 March 1942 Imperial General Headquarters had accorded Operation FS top strategic priority. Preparations for implementation of Operation FS were put in train immediately. However, on 2 April, the Commander in Chief of Japan's Combined Fleet, Admiral Isoroku Yamamoto, presented to Navy General Staff his own plan for a major offensive against America's Midway Atoll in the central Pacific. Yamamoto argued that an attack by Japan on the Midway Atoll would draw America's Pacific Fleet aircraft carriers to the defence of Midway where they could be annihilated by his Combined Fleet. Yamamoto also intended his Midway Operation to be the first stage of a subsequent major assault on Hawaii. Yamamoto's plan provided for the Midway offensive to begin early in June 1942, and for important aspects of Operation FS, namely, the capture of New Caledonia, Fiji and Samoa to be deferred until after the completion of his Midway Operation.

When presented to Navy General Staff, the Combined Fleet plan received a cold reception. The admirals of the Navy General Staff had grave reservations about Admiral Yamamoto's proposed Midway Operation which they viewed as a high risk gamble of dubious strategic worth. They argued that the decisive confrontation with the American Pacific Fleet should take place in the South-West Pacific where the Japanese warships could receive powerful support in the battle from nearby Japanese air and naval bases. However, Admiral Yamamoto remained obstinate. He insisted that the Combined Fleet confrontation with the United States Pacific Fleet must take place at Midway, and that the capture of New Caledonia, Fiji, and Samoa should be deferred until the completion of his Midway offensive. Faced with a threat by Yamamoto to resign unless his plan was accepted, Navy General Staff reluctantly agreed to his demands on 5 April.

While agreeing in principle that the decisive confrontation with the US Pacific Fleet would take place at Midway Atoll, Navy General Staff insisted that the Midway Operation be coupled with a simultaneous operation designed to capture and occupy islands in the Aleutian chain off the coast of Alaska. Navy General Staff remained highly sceptical about the timing of Yamamoto's plan and refused to agree that the Midway-Aleutian Operations should begin on 3 June 1942. Navy General Staff doubted whether preparations for the complex Midway and Aleutian Operations could be completed by 3 June and insisted that they be deferred until late June. Navy General Staff was unwilling to permit resources already allocated to Operation MO to be reallocated to the Midway-Aleutian offensives.

The impact of the Halsey-Doolittle Raid on Operation MO

Haggling over respective priorities of the Navy General Staff and Combined Fleet offensive plans, and in particular, the timing of the Midway-Aleutian operations, continued until 18 April 1942. On that day, American carrier-launched medium bombers struck Tokyo and other Japanese cities.

The bold Doolittle hit-and-run carrier raid produced a swift revision of Japan's strategic priorities. After the 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. Admiral Yamamoto's Midway plan was designed to extend Japan's eastern defensive perimeter to the Midway Atoll; to draw the aircraft carriers of the United States Pacific Fleet to a decisive battle at Midway where they could be destroyed; and to prepare the stage for a major Japanese assault on the Hawaiian islands. In the expectation that Yamamoto's plan would succeed and lead to complete destruction of the American Pacific Fleet, Imperial General Headquarters gave its approval for the Midway-Aleutian offensives to be launched on 3 June 1942.

The Halsey-Doolittle Raid on 18 April 1942 played a significant role in turning the tide of the Pacific War
against Japan. The USS Hornet launches B-25 medium bombers for a retaliatory raid on Japan.

Japan had now committed itself to simultaneous preparations for complex naval operations in the southern Pacific in May 1942 closely followed by even more complex naval operations in the central and northern Pacific in early June 1942.

Admiral Yamamoto agreed to provide Vice Admiral Inoue with two fleet carriers from Vice Admiral Nagumo's First Carrier Striking Force and one light carrier to support Operation MO. The higher priority accorded to Admiral Yamamoto's Midway-Aleutian Operations caused the timetable for Operation MO to be brought forward from late May to early May 1942. This was deemed necessary to enable the aircraft carriers supporting Operation MO to take part in the Midway-Aleutian offensives. Yamamoto pointed out to Admiral Inoue that he needed the three carriers for his Midway offensive, and that they must be released by 10 May to return to the Japanese naval base at Truk.

The planning for Operation MO

The capture of Port Moresby was to be preceded by seizure of the islands of Tulagi in the British Solomon Islands and Deboyne off the east coast of New Guinea. The Japanese intended to establish naval flying boat bases at both islands. The flying boats would then conduct patrols into the Coral Sea to monitor the eastern flank of the Port Moresby invasion force. The Japanese Tulagi invasion convoy would be supported by a covering force of warships under the command of Rear Admiral Aritomo Goto. The covering force would comprise the light aircraft carrier Shoho, four heavy cruisers, and one destroyer. After Admiral Goto's warships had covered the Tulagi landing, he would be required to withdraw his ships to the west and cover the Port Moresby invasion convoy of eleven transports, one light cruiser, and several destroyers as it moved towards Port Moresby. To deal with any attempt by an Allied naval force to oppose the Port Moresby and Tulagi landings, a powerful fleet aircraft carrier striking force would be present in the Coral Sea to support the Japanese invasion forces. This carrier force would be under the command of Vice Admiral Takeo Takagi.

These Japanese invasion plans directed against Australia would produce in the Coral Sea the first major fleet to fleet engagement between the American and Japanese navies following Pearl Harbor, and for the first time in naval history would see a major naval battle decided by opposing aircraft carriers.

British and American Code-breakers learn about Japan's Operation MO

In March 1942, British and American code-breakers intercepted Japanese Navy JN25 radio signals which indicated a forthcoming Japanese offensive towards Australia. On 3 April 1942, the American code-breakers at the HYPO Station in Hawaii, led by the brilliant cryptanalyst, Commander Joe Rochefort, intercepted a signal which indicated that an offensive would be mounted from the Japanese base at Rabaul in Australia's Territory of New Guinea. At Pearl Harbor, Commander Rochefort became convinced that the two targets of the impending Japanese offensive were Port Moresby and the British Solomon Islands which lay immediately to the east of the island of New Guinea.

Commander Rochefort's prediction was confirmed on 9 April when an intercepted JN25 signal revealed the presence of an "Operation MO" aircraft carrier strike force at Truk in Japan's Caroline Islands and an "RZP" invasion force ready to be launched from Rabaul. The British and American code-breakers already knew that "RZP" was the Japanese code reference for Port Moresby. In mid-April, British code-breakers in Ceylon (now Sri Lanka) intercepted JN25 naval signals which revealed that two aircraft carriers from Vice Admiral Nagumo's powerful First Carrier Striking Force, Shokaku and Zuikaku, had been detached from his carrier group for action related to Operation MO. The Allies now knew that the focus of the Japanese offensive would be the Coral Sea to the east of Australia's Cape York.

An Allied naval Force prepares to resist the Japanese Landings at Port Moresby and Tulagi

To meet the danger posed by Japan's Operation MO to lines of communication between the United States and Australia, an Allied naval task force was assembled by Admiral Nimitz in the Coral Sea between 1 and 4 May 1942. Rear Admiral Aubrey Fitch, commander of Task Force 11 centred on the carrier USS Lexington, was ordered to join Rear Admiral Frank J. Fletcher's Task Force 17, centred on USS Yorktown, in the Coral Sea. Yorktown arrived in the Coral Sea on 1 May after replenishing and maintenance at Tongatapu in the Tonga Islands. The two American carrier task forces were joined in the Coral Sea on 4 May by the former ANZAC Squadron commanded by Australian-born Rear Admiral John Crace of the Royal Navy aboard his flagship the heavy cruiser HMAS Australia. The ANZAC Squadron had been redesignated Task Force 44 for this Coral Sea operation, and now comprised HMAS Australia, the American heavy cruiser USS Chicago, the Australian light cruiser HMAS Hobart, and two American destroyers, USS Perkins and Walke. The ANZAC Squadron usually included the Australian light cruiser HMAS Canberra, but on this occasion Canberra was undergoing a refit in dry dock at Sydney. The three Allied Task Forces were combined under the designation Task Force 17. The combined Allied force, under the command of Rear Admiral Fletcher, was designated Task Force 17. Crace's cruiser squadron became Task Group 17.3 (Support Group).

The Japanese seize Tulagi

The movement of the Japanese Tulagi Invasion Group through the Solomon Islands was observed and reported by Australian Coastwatcher D. G. Kennedy on Santa Isabel Island. From intercepts of Japanese naval signals, Rear Admiral Fletcher learned on 3 May that the Japanese had landed at Tulagi after the small Australian garrison had been withdrawn. While Rear Admiral Fitch continued fuelling his ships, Fletcher moved Yorktown and her escort warships towards Tulagi for the purpose of attacking the Japanese invasion force.

The USS Yorktown (CV-5) is in the Coral Sea and preparing to launch aircraft.

When aircraft from Yorktown reached Tulagi at 6.30 a.m. on 4 May they found that Rear Admiral Goto's warships supporting the Tulagi landing (the covering force) had already withdrawn. Yorktown's aircraft attacked the remaining Japanese naval force and sank a destroyer and four landing barges. Yorktown's aircraft also destroyed five floatplanes, and damaged a destroyer and minelayer. The destruction of the floatplanes was important, because it denied the Japanese long range reconnaissance capability out of Tulagi.

A Japanese Carrier Force enters the Coral Sea to support their Port Moresby Invasion Force

From intelligence intercepts of Japanese naval signals, it became clear to Admiral Fletcher that the Japanese intended to move their Port Moresby invasion force through the Jomard Passage which separates the eastern tip of Papua from the islands of the Louisiade Archipelago. He left Tulagi and steamed south to rejoin the main Allied task force. After rejoining the task force on 5 May, Fletcher spent most of that day refuelling Yorktown from the American tanker Neosho .On the morning of 6 May, the odds against the Allied task force increased significantly when the separate Japanese carrier striking force under the command of Rear Admiral Takagi entered the Coral Sea to support the Port Moresby invasion. This powerful striking force comprised the fleet aircraft carriers Shokaku and Zuikaku, which were supported by two heavy cruisers and six destroyers. Admiral Takagi's first objective was to destroy any Allied naval force that he might find in the Coral Sea. His second objective was to support Japan's Port Moresby invasion force by bombing Australian military airfields between Townsville and Thursday Island.

Lacking the signal decoding capabilities of the British and Americans, the Japanese had no certain knowledge of the presence of American aircraft carriers in the Coral Sea, but after the devastating raid by American carrier-launched aircraft on their invasion transports at Lae and Salamaua on 10 March 1942, Admiral Takagi's carriers were in attendance to prevent a similar fate befalling Japan's Port Moresby invasion force.

Steering a south-easterly course across the Coral Sea, Admiral Takagi's carrier strike force quickly began to close the distance between it and Admiral Fletcher's carriers. At one point, the American and Japanese carrier forces were only 70 miles (112 km) apart, although both admirals were unaware that their enemy was within striking distance.

The Port Moresby Invasion Force approaches the eastern Tip of Papua

At midday on 6 May, American bombers from Australia located Rear Admiral Goto's light carrier Shoho and its supporting warships south of Bougainville where the Japanese ships had been refuelling. The covering force was half way between Tulagi and the Jomard Passage when located. Late on the afternoon of 6 May, with a view to ensuring its safety from Japanese attack, Admiral Fletcher ordered the tanker Neosho to withdraw to the south with a destroyer escort. He then ordered the Allied task force to set course for the Jomard Passage. Fletcher's strategy was to intercept the second and larger Japanese invasion force moving towards Port Moresby as it traversed the Jomard Passage. By midnight on 6 May, the Japanese Port Moresby invasion transports were approaching the northern entrance to the Jomard Passage, and Fletcher hoped to be within striking distance of these transports by daylight on 7 May.