The strategic significance of Port Moresby for Japan and the United States

Histories of the Battle of the Coral Sea variously describe it as being inconclusive, a tactical draw, a tactical defeat for the United States, or a strategic victory for the United States. The distinguished British naval historian Richard Hough described Coral Sea as "a strategic American victory" in The Longest Battle: The War at Sea 1939-45 (at page 173). In A Battle History of the Imperial Japanese Navy (1941-1945), American historian Professor Paul S. Dull notes the fact that Rear Admiral Fletcher deprived Admiral Yamamoto at Coral Sea of two of his best fleet carriers for the crucial Battle of Midway (4-6 June 1942) where even one additional carrier might very possibly have swung the battle in favour of the Japanese (1978 edition at page 129). However, in concluding his brief account of the battle, Professor Dull comments: "It is difficult to say who won the battle of the Coral Sea" (ibid).

Only one of these descriptions is correct. The Battle of the Coral Sea was in fact a crucial strategic victory for the United States and Australia. Differences of opinion between military historians require me to explain why this is so.

Professor Dull's book is a study of a series of naval battles and actions that took place in the Pacific and Indian Oceans between Pearl Harbor and the Japanese surrender. His use of Japanese naval sources makes his book a useful resource for students of Pacific War naval history. However, taking the Battle of the Coral Sea as an example, Professor Dull fails to place this battle in its correct historical context and fails to relate its outcome to achievement or non-achievement by the United States and Japan of their respective strategic aims in 1942. He incorrectly states (at page 116) that Operation MO (the capture of Port Moresby and Tulagi) was a Japanese Army initiative when it was in fact an initiative of Navy General Staff, prompted by Vice Admiral Shigeyoshi Inoue, commander of the 4th Fleet or South Seas Force. I find it particularly unfortunate that Professor Dull does not appear to understand that the failure of the Japanese Operation MO at Coral Sea was a devastating blow to Japan's strategic aims in the Pacific in 1942. If he did not understand that Coral Sea was a vital strategic victory for the Allies, then this probably explains his inability to determine who won the battle.

It is important to appreciate that Japan's high command was determined to capture Port Moresby in 1942, and this was a top strategic priority. With Port Moresby in Japanese hands, their fortified bases in New Guinea would be separated from Allied bombers based in Australia by an additional 500 kilometre (300 mile) expanse of the Coral Sea. The Japanese intended to anchor their southern defensive perimeter on Port Moresby, and then extend it across the Pacific to Fiji with the purpose of isolating Australia from the United States, and denying the Americans their major base in the South-West Pacific.

If the Japanese had won the Battle of the Coral Sea (7-8 May 1942), they would have been able to capture Port Moresby on the southern coast of what was then the Australian Territory of Papua and the island of Guadalcanal in the British Solomons. Using Port Moresby as a base, Japanese medium bombers would have been able to strike as far south as the coastal city of Rockhampton (two thirds of the way down the coast of Queensland). On the way, they could have bombed Cairns, Townsville, and Mackay. The State capital Brisbane would have been beyond the striking reach of Japanese medium bombers taking off from a Port Moresby airstrip. See "Author's Note" below. With Port Moresby in their hands, the Japanese would have been able to block the eastern sea approaches to Australia's northern port of Darwin. The capture of Port Moresby would have been an important first step towards severing Australia's vital lifeline to the United States. The second step would have been establishment of a major Japanese forward airbase on the island of Guadalcanal. Japanese land-based bombers on Guadalcanal could then strike far out into the Pacific to New Caledonia and intercept sea communications between the United States and Australia. Japanese demands for Australia's surrender would have been greatly strengthened as the noose around Australia was steadily tightened.

The capture of Port Moresby by the Japanese would have meant the loss by the Americans and Australians of their last base in New Guinea, and placed a large expanse of Coral Sea between Allied bombers in Australia and Japanese bases in New Guinea. Port Moresby was intended to be one of the springboards from which the Americans and Australians would launch their counter-offensive to drive the Japanese out of New Guinea and back to their home islands. The Commander in Chief of the US Navy, Admiral Ernest J. King, believed that it was much easier to hold territory than to recapture it after it had been lost to the Japanese and fortified by them. The extent of American concern to save Port Moresby can be gauged from the commitment of all four of the Pacific Fleet's precious operational fleet carriers to the Battle of the Coral Sea. As it turned out, the carriers Enterprise and Hornet failed to reach the Coral Sea in time to take part in the battle.

These facts explain why the Japanese were determined to capture Port Moresby and Guadalcanal throughout 1942, and why the United States Navy and the Australian Curtin government were equally determined to save both Port Moresby and Guadalcanal. The crucial Kokoda Campaign was fought between 21 July 1942 and 22 January 1943 to save Australia from the grave peril that would have arisen if Port Moresby fell into Japanese hands.

Finally, the capture of Port Moresby would have facilitated a Japanese landing on the Australian mainland when that became feasible.

Author's Note on the combat range of Japanese bombers in 1942

Many of Queensland's cities and towns would have been within striking range of Japanese land-based medium bombers if Japan had captured the airfield of Port Moresby in 1942. The Mitsubishi G4M medium bomber (code-name "Betty") had an operational range of 1,600 kilometres (994 miles). It would have had sufficient fuel to reach the coastal city of Mackay (half way down the coast of Queensland), drop its bomb load, and return to Port Moresby. The Mitsubishi G3M (Allied code-name "Nell") had an operational range of 2,076 kilometres (1,290 miles). The Nell bomber would have been able to reach and bomb the city of Rockhampton (two thirds of the way down the coast of Queensland) and return to Port Moresby. If US Marines had not captured the forward airbase on 7 August 1942 that the Japanese were building on Guadalcanal, Japanese bombers could have reached and bombed Allied bases on New Caledonia and the New Hebrides (now Vanuatu).

The inexplicable failure of Vice Admiral Inoue to exploit the American carrier withdrawal by capturing Port Moresby

Naval historian Richard Hough puts his finger on an important issue when he states: "..the American high command was puzzled to know why the Port Moresby invasion did not take place after the withdrawal of the American carrier force" (at page 172). Hough suggests that Vice Admiral Inoue would have been concerned about the threat to his invasion force from Allied land-based bombers and the loss of fighter cover for his transports when the carrier Shoho was sunk by American carrier aircraft on 7 May. The Shoho was carrying twelve fighter aircraft to cover the Port Moresby landing.

At first appearance, it appears to be a valid argument, and it was the one used by Vice Admiral Inoue himself to excuse his peremptory cancelling of Operation MO when, in terms of of tonnage sunk and irreplaceable offensive power lost, he could reasonably claim that Japan had achieved a tactical victory. Fearing that his invasion transports and their escort warships would be vulnerable to attack by land-based Allied aircraft without close support from Shoho's fighters, Vice Admiral Inoue decided on the evening of 8 May to withdraw the invasion fleet to Rabaul and postpone the capture of Port Moresby. That decision left Rear Admiral Crace's Australian-American cruiser squadron in sole possession of the battlefield, namely, the Coral Sea, from which the enemy had all departed by midnight on 8 May.

This decision by Inoue is difficult to understand because Japanese pilots had reported to him that one Lexington class carrier and a battleship had been sunk, and that a Yorktown class carrier had been almost certainly crippled. The reported sinking of a battleship may be a reference to the dramatic but failed bombing attack on HMAS Australia. In the context of the withdrawal of the surviving American carrier Yorktown from the battle on the afternoon of 8 May, this should have suggested to Inoue that Japan had won a significant tactical victory over the Allied naval forces at Coral Sea, and that the only remaining barrier between the still powerful Japanese invasion force and Port Moresby was Rear Admiral Crace's small cruiser squadron which faithfully maintained its blockade of the Jomard Passage until recalled to Australia on 10 May 1942.

The failure by Inoue to proceed with the Port Moresby landing after the withdrawal of Yorktown inevitably raises the question: Did the Japanese MO invasion fleet still have the capability to capture Port Moresby after the carrier battle had ended? In my view, the answer to that question would have to be in the affirmative if Inoue had been a more aggressive commander.

Although Shoho had been sunk, Inoue still had the use of the much larger carrier Zuikaku to cover the Port Moresby landing. Zuikaku was still fully operational even with an air group reduced from sixty-two to forty-five operational aircraft. About half of these aircraft had been recovered from the disabled Shokaku. After recovering both air groups, Zuikaku had twenty-four fully operational Zero fighters, whereas Shoho had only twelve fighters to cover the Port Moresby landing. By consolidating his various MO groups, Inoue would have had a powerful invasion force comprising the fleet carrier Zuikaku, six heavy cruisers, three light cruisers, thirteen destroyers, and seven submarines.

Inoue's warships could also have been closely supported by land-based bombers and Zero fighters from Lae and Rabaul. Rear Admiral Crace's squadron comprised only two heavy cruisers (HMAS Australia and USS Chicago), one light cruiser (HMAS Hobart), and three destroyers. Japanese reconnaissance seaplanes had mistakenly reported one of Crace's cruisers as being a battleship, but the sinking of the battleship Prince of Wales and battle-cruiser Repulse off Malaya on 10 December 1941had shown the Japanese how vulnerable battleships were to attack by land-based bombers. If the Australian admiral had seen fit to oppose the passage of the consolidated MO force, Inoue's warships and bombers should have been sufficient to sweep Crace's squadron out of the way and open a clear path to Port Moresby.

Having reached Port Moresby in this way, it is reasonable to question whether Inoue's MO force would have faced any significant difficulties in capturing the small Australian port. Japanese Rabaul-based aircraft had been bombing Port Moresby regularly since 3 February 1942. The Japanese airbase at Lae was only 300 kilometers (186 miles) from Port Moreby. Japanese bombers and Zero fighters from Lae and Rabaul could have supported the amphibious landing and, together with Zuikaku's twenty-four Zeros, should have been able to neutralise any opposition from Allied aircraft based at Port Moresby. MacArthur's B-17 heavy bombers based in northern Australia were notoriously inaccurate and unlikely to create any significant risk for the Japanese amphibious force.

The land defences of Port Moresby are unlikely to have been a major problem for the 5,000 combat toughened troops of Japan's South Seas Detachment. The Australian garrison comprised three battalions of Australian militia troops, or about 1,500 infantry. These militia troops were raw recruits with an average age of eighteen and a half. Their officers were mostly inexperienced. Instead of being trained to fight the Japanese, the militia recruits had been put to work as labourers on the docks and roads on their arrival in Port Moresby in 1941, and they lacked both military training and adequate equipment to defend the town. The fortifications of Port Moresby in April 1942 comprised two ancient naval guns, a field artillery regiment, a heavy anti-aircraft battery, and a few mobile anti-aircraft guns. At the time of the Battle of the Coral Sea, the militia defenders of Port Moresby had been graded and assigned the lowest combat efficiency rating of "F". The blame for this disgraceful neglect of the training and equipment of the Port Moresby garrison attaches inexorably to Generals MacArthur and Blamey who failed to acknowledge the Japanese threat to the town despite clear intelligence warnings. This neglect of the defences of Port Moresby by MacArthur and Blamey becomes even more difficult to understand in the light of evidence that both the Japanese and the Commander in Chief of the United States Pacific Fleet, Admiral Chester Nimitz, regarded Port Moresby as being of vital strategic importance.

I believe that we are left with only one plausible conclusion, namely, that Inoue abandoned the capture of Port Moresby on 8 May because he lost his nerve following the sinking of the light carrier Shoho and disabling of the fleet carrier Shokaku. Inoue's failure to seize the opportunity to capture Port Moresby after Lexington had been sunk and Yorktown withdrawn caused consternation in Japan's naval high command. The Battle of the Coral Sea was trumpeted to the Japanese public as a great victory for Japan, but privately, the admirals knew that Inoue's failure to capture Port Moresby when the prize was within his grasp had cost them one of Japan's most important strategic aims. Inoue was relieved of his command of the 4th Fleet and ordered back to Japan. He spent the rest of the war in relative obscurity as the commandant of a naval college.

The failure by Inoue to exploit the American carrier withdrawal at Coral Sea handed a strategic victory to the Allies

The Battle of the Coral Sea was the first of a series of vital battles in 1942 that would decide the fate of Australia and shape the course of the Pacific War. For the loss of the light aircraft carrier Shoho, and serious damage to the fleet carrier Shokaku, the Japanese had crippled the fleet oiler Neosho, sunk the destroyer Sims, inflicted serious damage on Yorktown, and caused the loss of Lexington which was one of the largest aircraft carriers in the world at that time. Having forced the withdrawal of the surviving American carrier Yorktown, Vice Admiral Inoue failed to exploit his advantage by capturing Port Moresby. His apparent failure of nerve threw away a tactical victory and handed a crucial strategic victory to the United States and Australia.

By failing to capture Port Moresby, the Japanese were denied the opportunity to extend their southern defensive perimeter to the edge of the Coral Sea. By failing to capture Port Moresby, the Japanese lost the base that was intended to be the anchor for a chain of fortified bases across the Pacific to Fiji. Those bases were intended to isolate Australia from the United States. Australia was spared intensified aerial bombardment from Port Moresby. The United States and Australia kept their vital foothold on the southern coast of the New Guinea mainland from which the Allied counter-offensive would be launched in 1943. These are the most readily apparent consequences of the failure by Inoue to exploit the American carrier withdrawal by capturing Port Moresby, but there were at least four more important gains for the Allies from the Battle of the Coral Sea.

Vice Admiral Inoue's apparent failure of nerve gave Australia time to deploy its best troops to defend Port Moreby

The withdrawal of the Japanese amphibious invasion force, and a second postponement of the capture of Port Moresby, gave the Allies vital time in which to reinforce Australian militia units in New Guinea with battle-seasoned Australian Imperial Force (AIF) units recently returned from the Middle East. Every man would be needed when the Japanese eventually decided in July 1942 to move combat-toughened troops of the South Seas Detachment along the Kokoda Track to capture Port Moresby by land. With 13,500 Japanese troops committed to the capture of Port Moresby, the construction of a major Japanese forward airbase on Guadalcanal was relegated to lower priority.

Coral Sea almost certainly laid the foundation for a successful American landing on Guadalcanal in 1942

If the Japanese amphibious invasion force had not been withdrawn, and Port Moresby had been captured immediately following the Battle of the Coral Sea, the Japanese timetable for occupying the whole of the Solomon chain of islands, including Guadalcanal, could have been brought back on track. With the Japanese timetable back on track, this would almost certainly have led to the Japanese airstrip on Guadalcanal becoming a heavily defended operational airbase before the end of July 1942. If that had happened, it is highly unlikely that the landing by US Marines on Guadalcanal could have taken place on 7 August 1942. If the Japanese had been able to fortify Guadalcanal and make it their own forward base, the course of the Pacific War would have been significantly altered and prolonged.

Coral Sea produced the Kokoda Campaign, and Kokoda kept 13,500 Japanese troops away from Guadalcanal

The Japanese naval defeat at the Battle of the Coral Sea led directly to the bloody battles between Australian and Japanese troops along the Kokoda Track and at Milne Bay between July and December 1942. The land battle for Port Moresby occupied at least 13,500 Japanese troops, including 5,000 crack troops of the South Seas Detachment, at the same time that US Marines on Guadalcanal were engaged in a struggle to hold their own against repeated and determined Japanese attempts to dislodge them. Kokoda and Guadalcanal were both bloody campaigns of attrition, and the Japanese lacked the military resources to maintain both campaigns simultaneously. The stubborn Australian defence of Port Moresby reduced Japan's capability to defeat the Marines on Guadalcanal, and the equally stubborn Marine defence of Henderson Field denied reinforcements for Major General Tomitaro Horii's South Seas Deatachment on the Kokoda Track.

Coral Sea laid the foundation for the great American naval victory at Midway

One very important aspect of the Battle of the Coral Sea has been overlooked by some historians. Shokaku and Zuikaku were two of Japan's six best front-line aircraft carriers. Although the Americans lost USS Lexington, Shokaku was badly damaged and both Japanese fleet carriers suffered significant losses of aircraft and experienced air crews. As a result, neither Japanese fleet carrier was able to participate in the crucial Battle of Midway in June 1942, where the presence of only one additional Japanese fleet carrier might have been sufficient to turn the tide of battle against the United States. If the United States had been defeated at the Battle of Midway, Japan would have achieved undisputed naval supremacy in the western Pacific Ocean and would have been able to invade the Australian mainland whenever it chose to do so.

Coral Sea provided an import boost to Allied morale

The Battle of the Coral Sea was an important morale booster for the Allies. For the first time since Pearl Harbor, the seemingly unstoppable Japanese offensive had been checked, and a Japanese invasion force had been repulsed.