In the spring of 1942, flushed with the success that they had achieved at the outbreak of the Pacific War, the Japanese embarked upon an ambitious new campaign. It was called Operation Mo, and it envisaged an extension of the Japanese defensive perimeter across the length and breadth of the South-West Pacific. It all stemmed from events that had taken place back in January, when the Japanese Navy seized Rabaul in the New Hebrides virtually unopposed and quickly transformed it into a major fleet base. Now protection of that base had to be given a high priority.
Port Moresby lies on the southern coast of New Guinea, near the northernmost tip of Australia. From its occupation Japan counted on being able to menace Australian ports and airfields (where they knew the Americans were busy sorting themselves out for a counter-offensive). It would open the way for a Japanese conquest of New Caledonia and that, in turn, might enable Japan to cut off the vital movement of military equipment and personnel already beginning to flow westwards from North America to Australia. Indeed the capture of Port Moresby, as some optimistic Japanese Army appreciation asserted, might even force Australia out of the war. The naval force needed for this operation appeared to be so small that, for once, the Army had the ready cooperation of the Navy, which, in a revival of a Japanese inter-service tradition going back hundreds of years, consented to convoy a Japanese Army landing-force. The Americans and the British agreed with the Japanese appreciation, and decided that, though still far from ready to offer serious opposition to the Japanese, the operation must be resisted.
It was several months after the Japanese took Rabaul when Imperial General Headquarters resolved to capture Port Moresby by a naval coup de main. This attack was scheduled for March. Then Japanese Intelligence reported that the Allied Powers were amassing forces to counter just such a move. Yamamoto ordered the operation to be delayed until early May. The Japanese then assembled a veritable armada of seventy ships, including two attack carriers detached from Admiral Nagumo’s force on their way back to Japan after the Indian Ocean campaign. An additional light carrier, the little 12,000-ton converted submarine tender Shōhō, was ordered to join the force. The fleet also included a seaplane tender, half a dozen heavy cruisers, three light cruisers, fifteen destroyers and fourteen Army troop transports.
To meet this formidable threat, the Allied Powers hurriedly assembled a scratch fleet comparable in size, including two American attack carriers, the Yorktown and the Lexington, together with a British battleship, two American battleships, four heavy cruisers, four light cruisers and seventeen destroyers.
Yamamoto split his forces in the South-West Pacific Operation into seven parts under the operational command of Admiral Inoue Shigeyoshi at Rabaul. The Port Moresby Transport Force, led by Rear-Admiral Abe Kōsō and consisting of twelve Army and Marine troop transports, a mine-layer and a number of supply vessels, was earmarked for the occupation of Port Moresby. It would be escorted by Rear-Admiral Kajioka Sadamichi’s small Port Moresby Attack Force of a light cruiser, five destroyers, a patrol boat and some other auxiliaries. Rear-Admiral Marumo Kuninori’s Close Cover Force, comprising two light cruisers, a seaplane carrier and three gunboats, would help protect the landing operations where required. The more powerful elements of Inoue’s fleet were divided into Vice-Admiral Takagi Takeo’s Carrier Strike Force, comprising two heavy carriers, the Zuikaku and Shōkaku, escorted by two heavy cruisers and six destroyers, and two support forces, both commanded by Rear-Admiral Gotō Aritomo, the first of which was designated as a Close Support Force and consisted of a light carrier accompanied by a single destroyer, and the Main Body Support Force, a powerful squadron of four heavy cruisers. The remaining section of the fleet was the Tulagi Invasion Force under Rear-Admiral Shima Kiyohide, consisting of two destroyers, two mine-layers, a troop transport and some auxiliary craft. Each of these forces was given a separate mission to accomplish in Yamamoto’s complicated plan, which relied upon precision timing and the convergence of sections from various points of the compass.
Knowing the main features of the Japanese plans – and that, of course, made all the difference – the USS Yorktown and the Lexington hoped to join forces in the New Hebrides, far to the south-east, and then to jump the Japanese at Rabaul as soon as the enemy’s attack developed. A mixed cruiser squadron of two Australian cruisers and the USS Chicago, under the command of Rear-Admiral J. G. Crace of the British Royal Navy, would rendezvous with the two American carriers as they joined forces to surprise the Japanese. The only other American carriers in the Pacific were on their way home to Pearl Harbor after having taken part in Jimmy Doolittle’s Raid over the Japanese mainland: ordered to the South Seas as soon as they refuelled, they arrived too late to take part in the action which followed.
In April 1942 Japanese assault forces opened Operation Mo with the subsidiary attack on Tulagi, an insignificant speck of land off the coast of Florida Island in the mid-Solomons, just twenty miles off a far larger island that was due to assume a greater significance in the months ahead: Guadalcanal. Acting on information derived from ‘Magic’ intercepts and augmented by the efficient ‘Coastwatcher’ bush-telegraph network organized by European and Australian planters and native islanders, the Australian garrison at Tulagi had been prudently withdrawn from the island before it could be overwhelmed. The Japanese saw nothing suspicious in this. They were intent upon their objective, which would soon be achieved, of transforming the island into a major seaplane base to protect the bastion which the Japanese were fast establishing at Rabaul, 600 miles to the north-west, and the eastern flank of the Japanese forces then fighting their way across New Guinea.
Confident of success, the Japanese anticipated that their next move would be to utilize the Tulagi Invasion Force to block off the back alley to their new property by taking Nauru Island and Ocean Island, 600 and 800 miles to the north-east. Then, secure in their new domains, the Japanese would be well placed to dispose of any forces sent out to dislodge them. Meanwhile, the assault on Port Moresby could be expected to entice the United States Pacific Fleet within range before it could recover from the losses it had sustained at Pearl Harbor. With good fortune, this might lead to the destruction of what remained of America’s offensive capabilities at sea. It was just possible that the Midway Operation might prove to be unnecessary.
The Japanese believed that they could rely upon speed to achieve their objectives before the arrival of any Allied counterstroke. The Midway Operation was already scheduled to take place in June, and Admiral Yamamoto Isoruku, a master at poker as well as at other games of chance, anticipated that he would need to place nearly the whole resources of the Imperial Navy in the stakes at Midway if his gamble there were to succeed.
The Japanese plan began to unravel almost at once. On 4 May the Port Moresby Transport Force and the Close Cover Force were in the Louisades, expecting to rendezvous with the Port Moresby Attack Force before rounding the tip of New Guinea on their way to Port Moresby (which was already under attack by a naval air fleet operating out of Rabaul). To the north, off New Georgia Island, lurked the Distant Cover Force which would have to protect the Japanese flanks during both the Tulagi and Port Moresby invasions. Having approached the Solomons from the north, the Japanese Carrier Attack Force shortly moved south-easterly to skirt the islands on a course which was to take it round San Cristobal. At this moment aircraft from the USS Yorktown intercepted the Tulagi Invasion Force and broke its back. The Yorktown, acting completely independently, hared off alone to the doorstep of Tulagi when a reconnaissance aircraft from Australia reported that the Japanese were busy disembarking their forces there. This seemed too good an opportunity to be missed. On this occasion it might have been better to wait.
Swathed in a protective blanket of cloud and closing upon their enemy at 27 knots, the Yorktown and her destroyer escort neared the mid-Solomons and in a series of three strikes delivered by Yorktown’s aircraft in rapid succession, the Americans created havoc in the harbour area. But the light force of Rear-Admiral Shima’s ships covering the Japanese landing were scarcely worth the effort. About half of that force was sunk, the seaplanes were cut to ribbons, and most of Shima’s other vessels sustained heavy damage. But this sally by the Yorktown had deprived the Americans both of surprise and of the significant trophies that would have justified the effort. Up to this point, the Japanese had been completely ignorant of the fact that there were any American carriers in the vicinity. The Japanese landing force was evacuated, apart from a small Army garrison left behind to keep an eye on things. It would not be long before the Japanese would return to re-establish themselves on the island in greater strength.
For the next two days, the two opposing carrier fleets moved uncertainly, if not nervously, towards their first direct clash of the war. On 5 May the Americans shot down a flying boat sent up from Rabaul to find them. The aircraft had no time to report the location of the Yorktown before it was intercepted: the effect of radar was already making itself felt in the Pacific War. It was not until almost twenty-four hours later that another Japanese Army flying boat from Rabaul found and reported the whereabouts of the American fleet. At about the same time, aircraft from the two fleets spotted their enemy’s vessels.
Shortly after dawn on 7 May the Japanese were the first to achieve any success when they hit an oil tanker and a destroyer, initially mistaken for a carrier and a cruiser. It was an expensive error, for in the general mêlée that followed, the Americans sank the almost defenceless little Shōhōwhile its aircraft were away hunting the American carriers without success: only exceptionally good fortune and the vagaries of the weather saved the American carriers from discovery. The two sides then played a game of cat and mouse interspersed with sporadic bursts of aerial combat. The fighting continued on 8 May. The numerical advantage lay with the American airmen, and their odds improved still further thanks to a 2:1 superiority in the anti-aircraft firepower of the American surface fleet. However, this was offset by the far superior skill, discipline and aircraft of the Japanese. The Shōkaku sustained severe damage. Her sister ship, the Zuikaku, was untouched. The USS Lexington sank, a lingering death, and the Yorktown suffered bomb damage, only narrowly escaping serious harm.
Both sides then began to limp away from further trouble. The Americans were in no position to continue the battle without running the risk of losing the Yorktown and other valuable ships as well. The Japanese were in a stronger position: the Zuikaku, thanks to aircraft landed from the Shōkaku as well as its own squadrons, carried a full complement of aircraft. Yamamoto, indeed, countermanded his fleet commander’s order and angrily signalled the Japanese to annihilate all that remained of the enemy force. His intervention came too late to alter the outcome of the battle. It produced no result other than to betray Yamamoto’s lack of confidence in his subordinate commanders and to delay the repair and replenishment of his battle-scarred naval forces. The Japanese invasion forces, however, abandoned their designs upon Port Moresby for the moment and finally lost their chances for good.
The Battle of the Coral Sea was the first major naval battle between the two opposing sides to demonstrate the strengths and weaknesses which were to affect the future course of the war. It was a conflict entirely different in character from what had occurred before.
By standards of subsequent phases of the Pacific War, the Battle of the Coral Sea was amateurish and not particularly costly. The Americans and Crace’s forces had lost sixty-six aircraft, 543 dead, the 42,000-ton USS Lexington, a single destroyer and a fleet oiler as well as the damage sustained by their only other carrier in the engagement, the USS Yorktown. The Japanese lost seventy-seven aircraft, 1,074 dead, the 12,000-ton carrier Shōhō, a destroyer and three auxiliary vessels. Strictly speaking, the Japanese had won the engagement but at a higher price than was immediately evident. Both of their other carriers in the engagement had been crippled. The two heavy aircraft-carriers returned safely to Japan, but in a condition which put them out of use for several months while undergoing repairs and the training of new flight crews. The absence of these two ships in the impending engagements was probably of decisive consequence.
There were lessons to absorb. The rival forces had never sailed within sight of one another, and the battle had resolved itself into a hunt for one another by their aircraft. It was the first naval battle in history to be decided by a struggle for air supremacy. The surface ships engaged in the action never exchanged fire.
The Japanese regarded the Battle of the Coral Sea as a success, although one costly enough to remind them of the possibilities of defeat. Tactically speaking, it was a Pyrrhic victory for the Japanese. In a wider context, the result was something of a draw. Japanese plotting officers and air controllers had proved themselves far superior to their enemy in the course of the battle, but Japanese combat communications and the coordination of their surface vessels had proved clumsy and unresponsive to the demands of a modern, highly mobile and rather confused mêlée. Beneath the un-edifying and exaggerated claims and counter-claims made by the two sides, the elan of the Japanese naval command never recovered.
The Americans, though they were concerned about the eventual loss of the Lexington, were not entirely displeased at the result of the battle, which had brought to an end the run of easy and almost insolent successes by the Japanese. As a result of the air battles, the Americans drew various tactical conclusions and strengthened the force of fighter aircraft on their carriers. Yamamoto, it began to be whispered abroad, had allowed his methods of warfare to outstrip the personnel which would have made these decisive. Against this, the hit-rate of the Japanese aircraft against the enemy warships had achieved a remarkable 58 per cent, confounding pre-war estimates where figures as low as 3 per cent had been bandied about.
Although the Battle of the Coral Sea weakened both sides on what was to be the eve of the Battle of Midway, the really important fact that would become apparent only in retrospect was that the Battle of the Coral Sea thwarted the Japanese attack on Port Moresby and with it their advance towards the northern approaches of Australia. This was to prove of great significance for the future development of the war.
After the Coral Sea campaign, the Japanese Army wanted to mount another attack on Port Moresby, this time by an overland assault. Once that objective had fallen into Japanese hands, the Army hoped to cross the Coral Sea and invade northern Australia in order to counter the forces which MacArthur was building up for the re-conquest of the Southern Regions. The Naval General Staff, in their turn, was anxious to sever the long line of communications between North America and Australia by seizing New Caledonia, Samoa and the Fiji Islands. This scheme was abandoned when Admiral Yamamoto’s Midway Island Campaign was adopted.