“Never again would the odds be so much in favour for the Japanese to capture a prize which offered massive strategic upside.”

By Peter Ingman

THE BATTLE OF the Coral Sea, fought in May 1942, was the first significant Japanese defeat of the Pacific War. The conventional view is that it represented a tactical victory for the empire but a strategic victory for the Allies. Most commonly, historians have described the contest as having “denied” the Japanese the capture of Port Moresby, the key Allied base in New Guinea. However, a new examination of the facts suggest Japanese over-cautiousness was a larger factor and Moresby was theirs for the taking.

In early 1942, Japanese offensive operations in the South Pacific were carried out by the Imperial Navy’s Fourth Fleet, commanded by Vice-Admiral Shigeyoshi Inoue. When Inoue’s forces first ventured into the theatre in January of 1942, they easily captured the strategic port town of Rabaul against only weak Australian opposition. Some weeks later, in March, the Japanese landed at Lae on the New Guinea mainland. During this operation, losses were suffered after a bold intervention by the U.S. Navy. The carriers USS Lexington and USS Yorktown sailed into the Gulf of Papua and launched a daring air strike over the towering Owen Stanley mountain range: a first for naval aviation.

The losses at Lae left Inoue calling for more carrier support prior to pressing further in his offensive. The result was Operation MO, a complex plan slated for early May whereby the Japanese would capture both Port Moresby and Tulagi. Moresby, the capital of the Australian territory of Papua, was an air base of increasing importance from where USAAF bombers could raid targets throughout New Guinea, including Rabaul. Tulagi was the capital of the Solomon Islands and close to Guadalcanal, where the Japanese planned to develop an air base of their own. To secure these two objectives, Inoue’s Fourth Fleet was allocated naval reinforcements, the most important of which were the fleet carriers Shokaku and Zuikaku.

The Moresby invasion force, which included seasoned troops from the Imperial Japanese Army’s 144^th Infantry Regiment, would likely capture the town with ease after landing there. The defences there were provided by an Australian infantry brigade made up of young and poorly trained militiamen. Thousands of other troops present were mainly from anti-aircraft, engineering and support units tasked with developing a series of airfields over a very large area. In fact, there were five fields within 14 miles of Port Moresby and another some 30 miles distant. The invasion force would have infiltrated such a large area with ease, and as soon as any of the airfields were captured the Japanese could fly in Zeros and other aircraft from nearby Lae.

The main problem in taking Moresby was the long sea journey from Rabaul. The fleet had to sail some 450 miles across the Solomon Sea, pass through the Louisiade Archipelago and then cover another 250 miles along the south coast of Papua. Further, the convoy was limited by its oldest and slowest ships. In all, the voyage would take six days! During this time, the flotilla would be vulnerable to air attack, especially as it made passage through the Louisiades and then navigated coral reefs along the Papuan coast.

Air cover for the convoy was vital, as the organic anti-aircraft defences of the transport ships and their escorts were very weak. Hence the importance of the fleet carriers Shokaku and Zuikaku. In addition, aircraft from the light carrier Shoho would help cover the convoy as would a significant force of floatplanes forward deployed to a lagoon in the Louisiades.

However, another factor that is often overlooked is the strength and disposition of the Japanese land-based air force. A peculiar feature of Operation MO was that as the convoy drew closer to Moresby it would benefit from stronger land-based air cover. This was because the Japanese airfield at Lae was only an hour’s flying time from Moresby, and the Zero fighter had a combat endurance of as much as six hours or more.

Following the Japanese capture of Tulagi on 3 May, the main naval actions of the Battle of the Coral Sea unfolded from May 4 to 8. The Japanese lost the light carrier Shoho, while the Shokaku was heavily damaged and forced to withdraw. On the American side the Lexington was sunk while the Yorktown was forced to withdraw due to aircraft losses and the want of fuel.

While the Japanese had sustained their own serious losses of carrier-based aircraft, the Zuikaku was undamaged and still had a very strong complement of Zeros. However, it was at this point that the Moresby invasion convoy was ordered back to Rabaul. It can be argued this was an overly cautious move by Inoue, who had evidently felt the loss of the Shoho keenly. It was first Japanese warship larger than a destroyer to be sunk in six months of war.

What were the risks to the Moresby invasion convoy if it proceeded? The greatest danger was that of attack by Allied land-based bombers, and to some extent the Japanese had been unnerved by the appearance of American B-17s. Lacking radar, the Japanese struggled to defend against high-altitude attacks by Flying Fortresses. However, the poor accuracy of bombing from such heights was yet to be fully appreciated by both sides.

Despite the convoy being a prime target for Allied bombers over several days, it did not suffer a single casualty. The attacks proved entirely ineffective, complicated by low clouds and confusion among air force crews unfamiliar with ship recognition and naval protocols. On one occasion a flight of B-17s mistakenly bombed friendly ships.

Just before the main Coral Sea battle began, a squadron of Australian and American cruisers and destroyers, under British Rear-Admiral John Crace, had been detached from the main American carrier force and placed in a blocking position just south of the Louisiades. However, lacking air cover the ships had only narrowly survived attack by land-based Japanese bombers on May 7. Nevertheless, the naval squadron would have posed a threat to the invasion convoy had it passed through the Louisiades. It was however itself at risk of being easily overpowered by four Japanese heavy cruisers nearby.

As it was, Crace’s squadron had withdrawn to Australia by the morning of May 10 due to mechanical problems and a lack of fuel. Fuel was not a problem for the Japanese, however, who had several tankers in the vicinity of the Shortland Islands. Indeed, in such circumstances the Japanese were comfortably in possession of the entire field-of-battle, making Inoue’s decision to cancel the Moresby invasion at this juncture all the more difficult to understand.

The only other force that posed a possible risk to the Moresby invasion convoy at this point was a second pair of American carriers, the USS Enterprise and USS Hornet, which had sailed from Hawaii in early May. These vessels only arrived in the waters east of the New Hebrides on May 11, and then had to spend a day refuelling. They were likely too late to have had any decisive impact on a Moresby invasion.

However, there are some serious questions as to whether the Enterprise and Hornet would have even intervened, had they the opportunity. The Japanese were quick to base flying boats at newly captured Tulagi, which greatly extended their reconnaissance coverage over the Coral Sea. This effectively denied the area to the American carriers, which were unlikely to operate where they were at risk of attack by land-based aircraft.

The greater strategic factor here was the Midway operation, which now loomed barely three weeks away and for which the Enterprise and Hornet were sorely needed. It is difficult to imagine U.S. naval headquarters putting these carriers in danger at this crucial time for the sake of Port Moresby. While Moresby was of huge strategic importance to General MacArthur’s South West Pacific Area command, it mattered little to the U.S. Navy in comparison to a potentially decisive engagement with the Japanese fleet off Midway Island.

So, it was that Inoue’s cancellation of the Moresby invasion would prove to be a fundamental strategic error. Never again would the odds be so much in favour for the Japanese to capture a prize which offered massive strategic upside. With hindsight Inoue’s action seems overly risk-averse, a mindset which probably dated from the initial failure of his Fourth Fleet to capture Wake Island back in December 1941. Months after the Battle of the Coral Sea Inoue was relieved of his command and served most of the remainder of the war as commander of the Japanese naval academy.

Peter Ingman is the co-author, with Michael Claringbould, of South Pacific Air War Volume 3 Coral Sea & Aftermath May – June 1942. This is the third volume in a trilogy chronicling the first six months of war in the South Pacific with full reference to both Allied and Japanese sources. The second volume, South Pacific Air War Volume 2 The Struggle for Moresby March-April 1942, was listed as one of the best global WWII books of 2018 by reviewer Stone & Stone.