'Mo' (ii) was the Japanese unsuccessful attempt to take Port Moresby in Papua (and in a parallel but successful operation Tulagi island near the south-eastern end of the Solomon islands group), leading to the Battle of the Coral Sea (3/7 May 1942).
This was a major turning point of the Pacific War, for it started the process in which the Allies successfully contested and then wrested the strategic initiative from the Japanese. It was also the world’s first naval battle in which aircraft carriers engaged each other by means of their embarked aircraft rather than their guns, and was the first naval battle in which the ships of neither side even sighted or fired directly upon those of the other. The battle can be considered a tactical victory for Japan as the US Navy lost the fleet carrier Lexington while Japan lost only the light carrier Shoho, but the Allies came to see the Battle of the Coral Sea as a significant strategic success as the Japanese direct threat toward Australia was stopped. The battle ended with no clear victor, but the damage suffered and experience gained by both sides set the stage for the Battle of Midway one month later.
New Guinea is the second largest island in the world, after Greenland, and is 1,306 miles (2101 km) long and some 500 miles (805 km) wide, with an area of 303,381 sq miles (785753 km²). Geologically part of Australia, the island is divided along its length by a central mountain range, which reaches to a height of 9,000 ft (27045 m) or greater along most of its length and is nearly impassable. The highest point is Carstentz Pyramid (now known as Puncak Jaya) at 16,024 ft (4884 m) in the western central portion of the island. The south-eastern part of the central range is known as the Owen Stanley Mountains, though the name was sometimes applied to the entire central range, and this part’s highest point is Mt Victoria, with a height of 13,360 ft (4072 m), located about 15 miles (24 km) to the west of Kokoda. The Owen Stanley Mountains possess rich mineral deposits, but in the period before World War II it was only gold which was deemed sufficiently valuable for miners to risk life and health in the area’s dire jungle environment. Much of the coast, particularly the north coast of Papua, was very poorly charted and was surrounded by dangerous reefs, and both sides hesitated to operate warships in these restricted waters.
New Guinea’s climate is extremely warm and wet, with rainfalls of 150 to 300 in (381 to 762 cm) per year. The north-west monsoon of the period between October and April is the wettest season, while the south-east monsoon of the period between April and September is drier and cooler, though only to a modest degree. The climate is slightly less harsh in the island’s south-eastern portion, and there are other regional variations. In particular, freezing temperatures occur in the central mountain range, and the highest peaks experience significant falls of snow. The island has a very high incidence of malaria, parasitic worms and leeches, making it extremely inhospitable.
The island is covered with dense jungle over its entire length, and in 1941 it was inhabited by perhaps 700 different tribes, most of which were still living in the stone age and with only the most vestigial contact with westerners. The native population was estimated at about one million persons, mostly Melanesian but with a considerably variety of physical characteristics, and there were no more than 6,000 European settlers on the island. These were concentrated largely in the east, and the 1936 census revealed that there were only 204 Europeans in the Dutch western end. Much of the island remained wholly unexplored, and there were virtually no roads. Jungle tracks connected local settlements, a few airstrips had been built by gold miners, and the Sepik river, which flows eastward into the sea in the area to the east of Wewak, was navigable for almost 300 miles (485 km). On the south coast, the Fly river is navigable for 500 miles (805 km), and much of its watershed is a vast trackless swamp. Thus Allied and Japanese aircrew who had to parachute into the New Guinea jungle were rarely seen again: some fell victim to headhunters, but most were simply lost in the jungle and starved.
Discovered in 1512, the island was occasionally visited but remained unclaimed until 1828, when the Dutch claimed the western half of the island. Germany claimed the north-east coast in 1884 and the British promptly responded by claiming the Papua peninsula to the south-east. The German and British territories were taken over by Australia following World War I, the German territory under a League of Nations mandate. By 1941, therefore, the administration of New Guinea was split between the Netherlands East Indies and Australia. The island was primitive in the extreme, and in 1941 its only significant ports were Port Moresby on the Australian end and Hollandia (now Jayapura) on the Dutch end.
The Australian half of the island was administered by the Australia-New Guinea Administrative Unit (ANGAU), which was comparatively enlightened in its treatment of the native peoples, requiring the use of Motuam, the dominant native dialect, in place of Pidgin. Though there were exceptions, such as the intensely warlike Orokaiva, the tribes who had had regular contact with the ANGAU tended to support the Allies, proving particularly effective as stretcher bearers. In 1939 the Australians organised the New Guinea Volunteer Rifles, a militia unit of approximately battalion strength, and the Papuan Infantry Battalion was raised from the local population in 1940, and two more native battalions were raised during the war.
The evacuation of all European women and children from New Guinea was ordered on 17 December 1941, following the Japanese 'B' (ii) landings on Borneo. At that time, the only organised forces under arms in New Guinea were a few hundred troops of the NGVR at Wau and a battalion at Port Moresby.
Port Moresby was the capital of Papua New Guinea, and was a small and poorly equipped port on the nearly landlocked Fairfax Harbour, usable only by smaller ships, for which there was only a single berthing. The population was about 2,600 persons, of whom 800 were Europeans. Bomber airfields were already under construction at the start of the war, as this was to be an important link in the air ferry route between the USA and the Philippine islands group. Only Kila Kila, some 3 miles (4.8 km) to the east of the port, was operational at the time war broke out, and the anti-aircraft defences were only a small number of 3-in (76.2-mm) guns and a few machine guns. There was limited copra, rubber and coffee production in the area, and gold and copper were mined in the nearby Owen Stanley mountain range at Wau and other places.
In December 1941, Port Moresby was protected by two obsolete coastal guns on Ela Hill covering the Basilisk Passage, which is the harbour’s entrance, and the garrison comprised the Papuan Infantry Battalion and 49th Battalion, both of which were militia units, and there were 12 Consolidated Catalina flying boats of Nos 11 and 20 Squadron based in the harbour. Ships in the harbour included the light cruiser Adelaide, 6,775-ton transport Katoomba and two cargo vessels.
Its strategic location, which allowed heavy bombers to stage through Port Moresby to attack Rabaul on New Britain, made Port Moresby the objective of two Japanese operations during the war. The first was the 'Mo' (ii) attempted seaborne invasion which led to the Battle of the Coral Sea, and the second was the Kokoda Trail campaign ('Ri'), which came close to achieving its objective before the Guadalcanal landings prompted the Japanese to divert their best efforts elsewhere.
Eventually the air base complex in the Port Moresby area included Kila Kila, Seven-Mile Airfield completed shortly after the start of the war with Japan, Five-Mile Airfield with two 6,000-ft (1830-m) paved runways, Twelve-Mile Airfield completed in May 1942 with a 4,500-ft (1370-m) packed gravel runway, Fourteen-Mile Airfield with a 5,300-ft (1615-m) earth runway surfaced with Marston mat, and Seventeen-Mile Airfield completed near a swamp. There was also Thirty-Mile Airfield used for dispersal and emergency landings. Each airfield was named initially for its distance from Port Moresby, but because of the potential for confusion, in November 1942 the airfields were renamed after airmen lost in combat.
Following the successful conclusion of the 'Centrifugal Offensive' with the fall of Java on 8 March 1942, well ahead of the schedule to which the Japanese had been working, Japanese planners began to feel that there was no need to pause to consolidate their conquests and build up their defensive perimeter as originally planned, and the Japanese losses in this initial offensive had been so light that the Japanese began to look for new worlds to conquer in which came to be called, unofficially, the 'Second Operational Phase'. Japanese pre-war planning had been based on naval losses in the 'Centrifugal Offensive' of 20% to 30%, but the Japanese had in fact lost only 23 warships, all of which were of destroyer size or smaller; 67 transport and cargo ships totalling 314,805 tons; a few hundred aircraft; and a few thousand personnel. Their astonishingly successful first series of offensive operations was misread by the Japanese planners, who totally failed to recognise that the Allies would learn from their experience, that the Allies would not suffer any form of national defeatism or collapse of morale, and that US mobilisation was certain to eliminate Japan’s military superiority in qualitative as well as quantitative terms. Rather than consolidate their conquests and build their pre-planned defensive perimeter, then seek a diplomatic settlement on favourable terms as originally planned, the Japanese began looking for new worlds to conquer. This later came to be characterised as 'Victory Disease', and the carelessness resulting from this attitude led to the Japanese setback in the Battle of the Coral Sea and the Japanese disaster in the Battle of Midway.
It should not be imagined, however, that 'Victory Disease' was wholly prevalent. For example, the Emperor Hirohito asked General Hajime Sugiyama, the chief-of-staff of the Japanese army’s general staff, if the fall of Singapore would be a suitable moment to seek a settlement with the UK, and most of the senior army commanders were anxious to end combat in the Pacific and China to facilitate a redeployment against the USSR which, to Japanese surprise, had survived the German 'Barbarossa' invasion of 1941.
The debate within the Japanese armed forces about the future course of the war came to an end on 7 March 1942 with a conference at Imperial General Headquarters which established the 'Second Operational Phase'. This was largely the strategy of the navy as the army was largely preoccupied with the war in China and Burma. The navy urged a direct invasion of Australia on the grounds that only three army divisions would be needed to seize this island continent’s important centres of population. The army felt that the navy had completely misconceived the requirements of such an undertaking, claiming that the actual requirement would be 12 divisions and 1.5 million tons of shipping. This led, inevitably, to a compromise 'solution', which envisaged the isolation of Australia, forcing it out of the war, and the seizure of the Hawaiian islands group as a forward base. These moves would then open the way for the seizure of Alaska, and some Japanese leaders even foresaw the seizure of parts of Australia and Washington and Oregon states in the continental USA. This, some Japanese believed, would service to make the Pacific Ocean a 'Japanese lake'.
As a result of the 7 March conference, the Japanese began to plan a series of advances along two axes which, in many respects, were the mirror images of of those which the Allied counter-offensive of 1943/44. The first blow would fall on Port Moresby and Tulagi island early in May 1942 as 'Mo' (ii), which would extend Japanese power over the Coral Sea and open the door to the New Hebrides islands group and New Caledonia. This would be followed by the capture of Midway and the western part of the Aleutian islands group during June in 'Mi' (ii) and 'Al'. In July The Japanese would turn their attention to the capture of the Fiji and Samoa island groups in 'Fs'. Finally, Hawaii would be assaulted in October. Admiral Isoroku Yamamoto, commander-in-chief of the Combined Fleet, believed that the smooth progress of the first-phase operations had given the Japanese an invincible strategic position which could not be maintained by going over to the defensive, and therefore that to secure this strategic situation the Japanese had to maintain the offensive and strike at the Allies' weak points one after another.
The Allied defensive strategy was shaped largely by Admiral Ernest J. King, the Chief of Naval Operations and Commander-in-Chief Fleet, who was not content with a defensive posture and thus waiting for the Japanese to do as they planned. King insisted that Admiral Chester W. Nimitz, commanding the Pacific Ocean Areas and the Pacific Fleet, instruct his forces to undertake carrier raids against outlying Japanese positions to keep them off-balance, while at the same time protecting the Hawaiian islands group and the maritime lines of communication with Australia and New Zealand. King also looked to the earliest possible implementation of a counter-offensive from the New Hebrides islands group up the chain of the Solomon islands group to Rabaul, and the first stage of this latter demand soon materialised as the Guadalcanal campaign.
The origins of the 'Mo' (ii) plan to take Port Moresby thus lay with the Japanese army, which saw in the primary aspect of the operation a major strategic opportunity for Japan to extent the southern perimeter of the 'Greater South-East Asia Co-Prosperity Sphere' by occupying the whole of the great island of New Guinea and completing its hold on the Solomon islands group so that they could sever the lines of maritime communication across the Pacific Ocean between the west coast of the continental USA and the east coast of Australia. Early in 1942, having conquered nearly all of South-East Asia in just a few months and at modest matériel and manpower cost, Japan was at the height of its military power.
The Allies had suffered a long series of sea, land and air defeats, were psychologically numbed at least in the short term by this long series of humiliating defeats, and were only just starting to build the skills and create the resources first for continued survival and then for the riposte. The Allied strategy at this time was focused on the build-up of the US Army and US Marine Corps on New Caledonia island, lying well to the south of the Solomon islands group, and of the Australian army and the Royal Australian Air Force units in the south and east of Papua, the Australian Territory of New Guinea, just to the north of Australia.
On 23 January 1942 Major General Tomitaro Horii’s South Seas Detachment of the Japanese army, under the overall command of Vice Admiral Shigeyoshi Inoue’s 4th Fleet, had taken Kavieng at the north-western tip of New Ireland and Rabaul on the north-eastern tip of New Britain in 'R'. The South Seas Detachment was a brigade-size force formed in 1941 as an army unit for service in the South Pacific after the Japanese seizure of Wake island and Guam in the Mariana islands group from the Americans and the Gilbert islands group from the British. As part of the South Seas Force, it fell under Japanese navy control, and the detachment comprised elements of Lieutenant General Hiroshi Takeuchi’s [e’55th Division.
The South Seas Detachment comprised the 144th Regiment (of the 55th Infantry Group) with 2,700 men, 1/55th Mountain Artillery Regiment with 750 men and 12 75-mm (2.95-in) mountain guns, 3rd Squadron of the 55th Cavalry Regiment, 1st Company of the 47th Anti-Aircraft Artillery Battalion, Infantry Gun Company of the 144th Regiment, and a number of engineer, signals and transport elements as well as thee medical detachments.
As noted above, the South Seas Detachment was to have been used for the seizure of Guam, but was diverted to Wake island after the initial unsuccessful attempt by the Japanese navy to seize the atoll, and later rejoined its parent formation, the 55th Division, for the New Guinea campaign.
After their capture of Kavieng and Rabaul, the Japanese had then embarked on a programme to build these two islands, in the Bismarck islands group lying to the north-east of the Australian-mandated territory of North-East New Guineas, into a bastion area from which their forces could check any Allied effort to move back toward the Netherlands East Indies, and also to pave the way for possible further expansion to the south and south-east. It was from Rabaul that, during April 1942, the Japanese forces launched a co-ordinated amphibious offensive whose two elements were 'Mo' (ii) designed to take Port Moresby, the main city and port of Papua, in the south-west, and 'Sn' to take Tulagi island of the Solomon islands group in the south-east. This pair of linked operations was designed to yield three objectives: the capture of Port Moresby that was the last possible Allied bastion between New Britain and northern Australia, the establishment of a seaplane base at Tulagi for control of the waters round the Solomon islands group and for reconnaissance of the areas farther to the north-east, east and south-east, and the enticement of the US aircraft carrier force, the last major surface warfare component of Nimitz’s Pacific Fleet, into combat under tactical conditions favourable to the Japanese navy.
Japan’s longer-term thinking remains uncertain, but there can be little doubt that Japan was already considering a major strengthening of its hold on the Solomon islands group as a bastion against any future US counter-offensive, and might also consider an invasion of northern Australia.
Japanese military planning had a predilection for complexity, resulting in ill-defined and often disputed areas of responsibility and bitter inter-service wrangling between the Japanese army and navy. So far as Japan’s longer-term intentions for the South Pacific were concerned, the one certainty was that any naval strategy would elicit a strongly promoted army counter-strategy, and vice versa. Commander of the Combined Fleet, Yamamoto was at this time preparing 'Mi' (ii) as his offensive to bring the Pacific Fleet to decisive battle on strategic and tactical terms advantageous to the Japanese, and argued against 'Mo' (ii) as a diminution of Japanese strategic effort. In the event both 'Mi' (ii) and 'Mo' (ii) were implemented in a closely spaced sequence, resulting in a great dilution of effort and strength.
A Japanese bombing campaign to disrupt the Australian defences of North-East New Guinea and Papua had already been started, beginning with air attacks on Lae and Salamaua on 21 January as a preface to the Japanese move against Rabaul, whose new bomber base permitted an extension of the Japanese offensive activities as far to the south-east as Bougainville island in the Solomon islands group and as far to the south as Port Moresby (first raid on 3 February) on the south coast of Papua. Port Moresby featured strongly in Japanese planning, for its harbour and anchorage offered just the base needed for Japanese warships to threaten northern and eastern Australia.
To ease the task of bombing Port Moresby, some 550 miles (885 km) from Rabaul, the Japanese decided on 'Ri' to seize bases in North-East New Guinea in the form of Lae as the site of a forward airfield and Salamaua to cover Lae. On 8 March one battalion of the South Seas Detachment's 144th Regiment occupied Salamaua while the 4th Fleet's 2nd Maizuru Special Landing Force occupied Lae and began work on the airfield.
A serious dispute now exacerbated the already strained relations between the headquarters of the Japanese army and of the Japanese navy in Tokyo, for the navy wished to seize Australia as a means of depriving the Allies of their major bastion in the region, while the army demurred on the grounds that the task would need some 12 divisions and 1 million tons of shipping. By the end of March a compromise had been reached, the navy agreeing to the occupation of all New Guinea at the same time as Samoa, Fiji and New Caledonia were taken in 'Fs', which would sever the maritime lines of communications between the USA and Australia, where General Douglas MacArthur had just arrived as commander-in-chief of the Allies' South-West Pacific Area command. 'Fs' was then postponed in favour of the navy-sponsored 'Mi' (ii), though a more limited local offensive was retained in 'Mo' (ii), an amphibious attack on Port Moresby, with a secondary operation against Tulagi mounted in parallel as 'Sn' for the establishment of a seaplane base to reconnoitre far along the Allied lines of maritime communication across the Pacific. Once Tulagi had been secured, these forces were then to take Nauru and Ocean islands yet farther to the south-east in 'Ry'.
The accelerated schedule for 'Mo' (ii) meant that most of the carriers of Vice Admiral Chuichi Nagumo’s 1st Air Fleet would not be able to participate in the New Guinea operation. After five months of intensive operations, from the 'Ai' attack on Pearl Harbor raid to the 'C' raid into the Indian Ocean, the 1st Air Fleet was in sore need of a pause in its operations for refit of its ships and replenishment of its air groups. Only the fleet carriers Shokaku and Zuikaku could be ready in time for the New Guinea operation, and in the meantime the other four fleet carriers would be prepared for the 'Mi' (ii) undertaking against Midway island. Neither Yamamoto and his staff nor the navy’s staff anticipated any serious difficulties with either operation.
Overall command of 'Mo' (ii) was vested in the 4th Fleet, and Horii issued his orders on 29 April for landings scheduled to fall on Port Moresby during 10 May. Drafted under Inouye’s supervision, the naval plan was of typical complexity, involving no fewer than seven elements under separate commanders with Rear Admiral Aritomo Goto in overall tactical command. 1
It was only to be expected that the US Navy would not let these operations proceed unhindered, so the Japanese included a powerful seventh element in the form of Vice Admiral Takeo Takagi’s Carrier Strike Force (fleet carriers Zuikaku with 21 A6M fighters, 21 Aichi D3A 'Val' dive-bombers and 21 B5N bombers, and Shokaku with 21 A6M fighters, 20 D3A dive-bombers and 21 B5N bombers, heavy cruisers Myoko and Haguro, and destroyers Ariake, Yugure, Shiratsuyu and Shigure of Destroyer Division 27 and Ushio and Akebono of Destroyer Division 7, and oiler Toho Maru), which was to sail from Truk atoll in the Caroline islands group on 1 May to pass round the south-eastern end of the Solomon islands group and then enter the Coral Sea, so getting to the east of any US naval forces (believed by Inoue to be no more than one carrier plus supporting ships) which might intervene, and thus forcing them into battle.
Reduced to its basic components, therefore, the Japanese plan comprised the initial 'Sn' (ii) capture of Tulagi on 3 May to protect the eastern flank of the operation’s next and major phase, the 'Mo' (ii) capture of Port Moresby. The Carrier Strike Force was to cover the Tulagi operation and then proceed down the eastern side of the Solomon islands group, swing round the eastern tip of the island chain, and finally head to the west into the Coral Sea as protection for the Port Moresby invasion force.
At the same time, men of the Close Cover Force would occupy Deboyne island, just off the east coast of New Guinea, as a base from which its seaplanes could scout for the Port Moresby invasion force.
Despite the fact that it had been modified from 1 November 1941, as part of the Japanese precautions before the 'Ai' attack on Pearl Harbor, the Japanese naval code had been partially broken once more by the Americans, and on the basis of the resulting 'Ultra' intelligence Nimitz was aware of the Japanese plans and could thus prepare a fateful counter, though he was also well aware of the numerical inferiority of the naval strength he could muster under Rear Admiral Frank J. Fletcher, who was despatched with Task Force 17, centred on the fleet carrier Yorktown, from Tongatabu island in the Tonga islands group on 27 April to link with Rear Admiral Aubrey W. Fitch’s TF11, centred on the fleet carrier Lexington, at Point Butternut, some 300 miles (485 km) to the south-east of Guadalcanal, during the afternoon of 1 May. Vice Admiral William F. Halsey, the commander Carriers, Pacific Fleet, was just returning from 'Conceal' (the 'Doolittle raid') and was immediately sent to the Coral Sea with the fleet carriers Enterprise and Hornet, but did not arrive in time for the battle.
This was TF17 comprising what was now Task Group 17.5 or Carrier Group (fleet carrier Yorktown with 21 Grumman F4F fighters, 38 Douglas SBD dive-bombers and 13 Douglas TBD torpedo bombers, fleet carrier Lexington with 23 F4F, 36 SBD and 13 TBD aircraft, and destroyers Morris, Anderson, Hammann and Russell), Rear Admiral Thomas C. Kinkaid’s TG17.2 or Attack Group (heavy cruisers Minneapolis and New Orleans, and under the command of Rear Admiral William W. Smith, Astoria, Chester and Portland, and destroyers Phelps, Dewey, Farragut, Aylwin and Monaghan) and Australian Rear Admiral J. G. Crace’s TG17.3 or Support Group (Australian heavy cruisers Australia and light cruiser Hobart, US heavy cruiser Chicago, and US destroyers Perkins and Walke), this last despatched from Australia at MacArthur’s instigation; other Allied elements were TG17.6 or Fuelling Group (oilers Neosho and Tippecanoe, and destroyers Sims and Worden), and TG17.9 or Search Group (seaplane tender Tangier at Nouméa, New Caledonia, with 12 Consolidated PBY-5 flying boats).
Other US elements in the theatre were land-based air and submarine forces. Major General George Brett’s Allied air forces comprised the 3rd Light Bombardment Group (19 North American B-25 Mitchell medium bombers, 19 Douglas A-24 dive-bombers and 14 Douglas A-20 attacks bombers) at Charters Towers, 22nd Medium Bombardment Group (12 B-25 and 80 Martin B-26 Marauder medium bombers) at Townsville, 8th Fighter Group (50 Bell P-39 fighters at Port Moresby and 50 P-39 fighters at Townsville), 19th Heavy Bombardment Group (48 Boeing B-17 Flying Fortress heavy bombers) at Cloncurry, 49th Fighter Group (90 Curtiss P-40 fighters) at Darwin, and 35th Fighter Group (100 P-39 fighters) at Sydney.
Rear Admiral Francis W. Rockwell’s TF42 or Eastern Australia Submarine Group comprised Task Group 42.1 with the submarine tender Griffin and submarines S-42, S-43, S-44, S-45, S-46 and S-47 (Submarine Division 53), and S-37, S-38, S-39, S-40 and S-41 (Submarine Division 201).
Fletcher possessed intelligence information which suggested that the Japanese had at least three, and possibly as many as five, carriers in the area. He also had a healthy respect for Japanese land-based air power operating from the Rabaul area. He therefore planned to keep his carriers just outside the radius of Japanese reconnaissance aircraft and await any opportunity which presented itself to descend on any Japanese force which moved out from the umbrella of protection afforded by Japanese air power. Fletcher wisely chose to merge his cruiser-based task force and Fitch’s carrier-based task force but, as the two carriers had considerably different turning radii, expected the carriers to evade independently if attacked, with the screen instructed to divide itself between the two carriers. Fletcher also designated two surface attack/support groups as TG 17.2 under Kinkaid’s command and TG 17.3 under Crace’s command. Fletcher resisted the temptation to shift his flag from a carrier to a cruiser, so that he could lead any surface attack personally, on the grounds that a cruiser lacked a carrier’s communications facilities. Fitch was designated as the air group commander and would retain a screen of four destroyers.
This plan was completely orthodox for the time, strongly resembling American pre-war fleet exercises, and was optimised for tactical flexibility.
Each side had land-based air support, but the commander of neither carrier task force had direct control of the land-based air units.
It was at 08.16 on 5 May that TF17 linked with Fitch’s TF11 and Crace’s TF44 at the prearranged Point Butternut to the south of Guadalcanal. At about the same time, four F4F fighters launched by Yorktown intercepted a Kawanishi H6K 'Mavis' reconnaissance flying boat of the Yokohama Air Group of the 25th Air Flotilla based at the Shortland islands, just to the south-east of Bougainville island, and shot it down 13 miles (21 km) from TF11. The 'boat was unable to send a report before it crashed, but its failure to return to base prompted the Japanese into the correct assumption that the 'boat had been shot down by carrierborne aircraft.
Pearl Harbor notified Fletcher that radio intelligence deduced the Japanese planned to land their troops at Port Moresby on 10 May and that their fleet carriers would probably be operating close to the invasion convoy. Armed with this information, Fletcher ordered the ships of TF17 to refuel from Neosho, and once the refuelling had been completed on 6 May, Fletcher planned to take his forces north toward the Louisiade islands group, to the south-east of New Guinea with the Solomon Sea to their north and the Coral Sea to their south, and do battle on 7 May.
Takagi’s carrier force meanwhile steamed down the eastern side of the Solomon islands group throughout 5 May, turned to the west to pass to the south of San Cristobal island, and entered the Coral Sea after passing between Guadalcanal and Rennell island to Guadalcanal’s south early in the morning of 6 May. Takagi began to have his ships refuel at a location about 210 miles (340 km) to the west of Tulagi island in preparation for the carrier battle he expected would take place on the following day.
It was on 6 May that Fletcher absorbed TF11 and TF44 into his TF17 as part of its TG17.5 and as as TG17.3 respectively. Believing the Japanese carriers were still well to the north near Bougainville island, Fletcher continued to refuel. Air reconnaissance patrols flown from the US carriers throughout the day failed to locate any of the Japanese naval forces as these latter were located just beyond scout aircraft range. However, at 10.00 a Kawanishi reconnaissance flying boat from Tulagi island sighted and reported TF17, Takagi receiving the report at 10.50. At this time, Takagi’s force was about 350 miles (565 km) to the north of Fletcher’s force, near the maximum range for his carrierborne aircraft. With his ships still refuelling, Takagi was not yet ready to enter action: based on the sighting report, Takagi also concluded that TF17 was heading to the south and thereby increasing the distance between the Japanese and US forces. Furthermore, Fletcher’s ships were steaming under a large and low-hanging overcast, which Takagi and Hara felt would make it difficult for their aircraft to find the US carriers. However, Takagi detached his two carriers with two destroyers under Hara’s command to make for TF17 at 20 kt in order to be in position to deliver an attack at first light on the following day while the rest of his ships completed refuelling.
Australia-based B-17 bombers staged through Port Moresby and attacked the approaching 'Mo' (ii) invasion force, including Goto’s warships, several times during 6 May, but failed to achieve any success. MacArthur’s headquarters radioed Fletcher with reports of the attacks and the locations of the Japanese invasion forces. The reports of USAAF crews that they had seen a carrier (in fact the light carrier Shoho) about 490 miles (790 km) to the north-west of TF17 further convinced Fletcher that the invasion force was accompanied by fleet carriers.
At 18.00 TF17’s ships completed fuelling and Fletcher detached Neosho and the destroyer Sims to take station farther to the south at a prearranged rendezvous point. TF17 then turned to head north-west towards Rossel island in the Louisiade islands group. Unknown to each other, the two side’s carriers were only some 80 miles (130 km) away from each other by 20.00 that night. At this time Hara reversed course to meet Takagi, whose ships had completed refueling and were now heading in Hara’s direction.
Late on 6 May or early on 7 May, Kamikawa Maru set up a seaplane base in the lagoon of Deboyne island of the Louisiade islands group with a view to helping in the provision of air support for the 'Mo' (ii) invasion force as it approached Port Moresby, and the rest of Marumo’s Support Group then took station near the D’Entrecasteaux islands group, to the north of Papua’s eastern tip, in order to help screen Abe’s oncoming Transport Unit convoy.
At 06.25 on 7 May, TF17 was some 130 miles (210 km) to the south of Rossel island, and at this time, Fletcher sent the cruisers and destroyers of Crace’s TG17.3 to block the Jomard Passage between the Louisiade islands group and the eastern end of Papua. Fletcher understood that Crace would be operating without air cover as TF17’s carriers would be committed to the task of locating and attacking the Japanese carriers. The detachment of Crace’s ships reduced the anti-aircraft defences available for the protection of the US carriers, but Fletcher had decided that the risk was necessary in order to ensure that the Japanese invasion force could not slip through to Port Moresby while he was engaged with the Japanese carriers.
Believing that Takagi’s carrier force was somewhere to the north of his own position, in the vicinity of the Louisiade islands group, Fletcher directed Yorktown to send 10 SBD dive-bombers to search that area, beginning at 06.19. Meanwhile Takagi, located about 350 miles (565 km) to the east of Fletcher, launched 12 B5N aircraft at 06.00 to scout for TF17. Hara believed that Fletcher’s ships were located to the south and advised Takagi to send the aircraft to search that area. At about the same time, Goto’s cruisers Kinugasa and Furutaka launched four Kawanishi E7K 'Alf' floatplanes to search to the south-east of the Louisiade islands group. Augmenting this search were several floatplanes from Deboyne atoll, four H6K flying boats from Tulagi island, and three Mitsubishi G4M 'Betty' medium bombers from Rabaul. Both sides prepared the rest of their carrierborne attack aircraft for launch immediately after the enemy had been located.
At 07.22 one of Takagi’s reconnaissance aircraft, from Shokaku, reported that it sighted US ships bearing 182° at a distance of 190 miles (305 km), and then at 07.45 confirmed that it had located one carrier, one cruiser and three destroyers. Another aeroplane from Shokaku soon confirmed the sighting. But what Shokaku's aircraft had actually sighted but misidentified were Neosho and Sims. Believing that the US carriers had been located, with Takagi’s agreement Hara immediately launched all of his available aircraft. A total of 78 aircraft (18 A6M fighters, 36 D3A dive-bombers and 24 B5N torpedo bombers) began to lift off Shokaku and Zuikaku at 08.00, and by 08.15 were on their way toward the reported sighting.
At 08.20, one of Furutaka's floatplanes located the US carriers and immediately reported it to Inoue’s headquarters at Rabaul, which forwarded the report to Takagi. The sighting was confirmed by one of Kinugasa's floatplanes at 08.30. confused by the conflicting sighting reports they were receiving, Takagi and Hara decided to continue with the attack on the ships to the south, but turned their carriers toward the north-west to close the distance with the reported sighting by the cruisers' floatplanes. Takagi and Hara considered that the conflicting reports might mean that the US carrier force was operating in two separate groups.
At 08.15, an SBD from Yorktown sighted Goto’s force screening the 'Mo' (ii) invasion convoy. Making an error in his coded message, the US pilot reported the sighting as 'two carriers and four heavy cruisers' some 260 miles (420 km) to the north-west of TF17. Fletcher concluded that the Japanese main carrier force had now been located and ordered the launch of all available aircraft to attack, and by 10.13 the US attack wave of 93 aircraft (18 F4F, 53 SBD and 22 TBD machines) was on its way. At 10.19 the SBD scout landed and its pilot discovered his coding error. Although Goto’s force included Shoho, the pilot thought that he saw two cruisers and four destroyers. At 10.12, however, Fletcher received a report, from a flight of three B-17 bombers, of an aircraft carrier, 10 transports and 16 warships about 35 miles (55 km) to the south of the SBD’s sighting. The bomber crews had actually saw the same thing as the SBD’s crew: Shoho, Goto’s cruisers and the Port Moresby invasion force. Believing that the B-17 sighting was of the main Japanese carrier force, Fletcher directed the airborne strike force towards this target.
At 09.15 Takagi’s attack force reached its target area, sighted Neosho and Sims, and searched in vain for the US carriers supposed to be in the area. Finally, at 10.51 the crews of Shokaku's reconnaissance aircraft realised that they had erred in their identification of the oiler and destroyer as aircraft carriers, and Takagi now appreciated that the US carriers were between him and the invasion convoy, and that the invasion forces was therefore in extreme danger. Takagi ordered his aircraft to attack Neosho and Sims without delay and then to return to their carriers as quickly as possible. At 11.15, the torpedo bombers and fighters abandoned the mission and turned back toward their carriers without expending their ordnance while the 36 dive-bombers attacked the two US ships. Four D3A aircraft attacked Sims and the rest dived on Neosho. The destroyer was hit by three bombs, broke in half, and sank immediately, all but 14 of her 192-man crew dying. Neosho was hit by seven bombs and then one of the dive-bombers, hit by anti-aircraft fire, crashed into the oiler. Heavily damaged and without power, Neosho was left drifting and slowly sinking, but before losing power had been able to notify Fletcher by radio that she was under attack and in trouble, but further details about who or what was attacking her were garbled, and the wrong co-ordinates for her position were given.
The US attack aircraft sighted Shoho a short distance to the north-east of St Aignan island in the Louisiade islands group at 10.40 and deployed to attack. The Japanese carrier was protected by a combat air patrol of six A6M and two Mitsubishi A5M 'Claude' fighters as the rest of the carrier’s aircraft were being prepared below decks for an attack on the US carriers. Goto’s cruisers surrounded the carrier in a diamond formation between 3,000 and 5,000 yards (2,745 and 4570 m) from the carrier. Attacking first, Lexington's air group, led by Commander William B. Ault, hit Shoho with two 1,000-lb (454-kg) bombs and five torpedoes, causing severe damage. At 11.00, Yorktown's air group attacked the burning and now almost stationary carrier, scoring with as many as 11 1,000-lb (454-kg) bombs and at least two torpedoes. Shoho sank at 11.35.
Fearing more air attacks, Goto now withdrew his warships to the north, but at 14.00 detached the destroyer Sazanami to rescue survivors: only 203 men of the carrier’s 834-man crew were recovered. Three US aircraft had been lost in the attack, these being two SBDs from Lexington and one from Yorktown. All of Shoho's aircraft were lost, though three of the combat air patrol pilots were able to ditch the fighters at Deboyne island and survived. At 12.10, using a prearranged message to signal TF17 on the success of the mission, Lexington's SBD squadron commander, Robert E. Dixon, radioed 'Scratch one flat top! Signed Bob.'
The US aircraft had returned and landed on their carriers by 13.38, and by 14.20 had been rearmed and readied to launch against the Port Moresby invasion force or Goto’s cruisers. Fletcher was concerned, however, that the whereabouts of the Japanese fleet carriers were still unknown. Fletcher had been informed that Allied intelligence believed that up to four Japanese carriers might be supporting the 'Mo' (ii) operation, and decided that by the time his reconnaissance aircraft had located the remaining Japanese carriers it would be too late in the day to make an attack. Fletcher therefore decided not to launch another attack on this day and remain concealed under the thick overcast with fighters ready to protect his ships, and turned TF17 to the south-west.
Informed of the loss of Shoho, Inoue ordered the invasion convoy to effect a temporary withdraw to the north and ordered Takagi, at this time located 260 miles (420 km) to the east of TF17, to destroy the US carrier force. As the invasion convoy reversed course, it was attacked by eight B-17 bombers, which scored no hits. Goto and Kajioka were told to assemble their ships to the south of Rossel island for a night surface action in the event that the US ships came within range.
At 12.40 a seaplane from Deboyne atoll sighted and reported Crace’s cruiser force some 80 miles (130 km) to the south of of Deboyne. At 13.15, an aeroplane from Rabaul sighted Crace’s force but made a faulty sighting report indicating the presence of two carriers 130 km (210 km) to the south-west of Deboyne island. These reports persuaded Takagi, who was still awaiting the return of all of his aircraft from the attack on Neosho, to turn his carriers due west at 13.30, and Takagi also advised Inoue at 15.00 that the US carriers were at least 490 miles (790 km) to the west of his current location and that he would therefore be unable to attack them that day.
Inoue’s staff now ordered two groups of attack aircraft from Rabaul, already airborne since that morning, toward Crace’s reported position. The first group included 12 torpedo-armed G4M bombers and the second group comprised 19 Mitsubishi G3M 'Nell' land attack aircraft armed with bombs. Both groups found and attacked Crace’s ships at 14.30 and claimed to have sunk a 'California' class battleship and damaged another battleship and a cruiser. In reality, Crace’s ships were undamaged and shot down four G4M machines. A short time later, three B-17 bombers mistakenly bombed Crace’s ships, but caused neither damage nor casualties.
At 15.26 Crace radioed Fletcher he could not complete his mission without air support, and then retired to the south to a position about 250 miles (400 km) to the south-east of Port Moresby to increase the range from Japanese carrier- or land-based aircraft while remaining close enough to intercept any Japanese naval forces advancing beyond the Louisiade islands group through either the Jomard Passage or the China Strait. Crace’s ships were low on fuel, and as Fletcher was maintaining radio silence (and had not informed him in advance), Crace had no idea of Fletcher’s location, status or intention.
Shortly after 15.00, Zuikaku monitored a message from a Deboyne-based reconnaissance aeroplane reporting (incorrectly) that Crace’s force had altered course to the south-east. Takagi’s staff assumed the aeroplane was shadowing the US carriers and came to the conclusion that if the Allied ships maintained the same course they would be within attack range shortly before the fall of night. Takagi and Hara determined to attack immediately with a select group of aircraft, less fighter escort, even though it meant the attacking aircraft would have to return after dark.
In an effort to confirm the location of the US carriers, at 15.15 Hara sent a flight of eight torpedo bombers to reconnoitre 230 miles (370 km) to the west. Ay about that same time, the dive-bombers returned from their attack on Neosho and landed, six of their pilots then being informed that they would be departing immediately on another mission. Choosing his most experienced aircrews, at 16.15 Hara launched 12 dive-bombers and 15 torpedo bombers with instructions to very slight to the north of west out to a radius of 320 miles (515 km). The eight scout aircraft reached the end of their 230-mile (370-km) search leg and turned back without seeing Fletcher’s ships.
At 17.47, operating under thick overcast 230 miles (370 km) to the west of Takagi’s ship, TF17 detected the Japanese attack on radar heading in its direction, turned south-east into the wind, and vectored 11 F4F fighters of the combat air patrol to intercept. Taking the Japanese formation by surprise, the US fighters shot down seven torpedo bombers and one dive-bomber, and heavily damaged another torpedo bomber, which later crashed, for the loss of three of its own number. After its heavy losses in the attack, which had also scattered their formations, the leaders of the Japanese attack conferred by radio and called off their mission. The Japanese aircraft jettisoned their ordnance and reversed course to return to their carriers. The sun set at 18.30, and several of the Japanese dive-bombers stumbled across the US carriers in the darkness, at about 19.00, and briefly confused as to their identity circled in preparation for landing before anti-aircraft fire from TF17’s destroyers drove them away.
By 20.00 TF17 and the Carrier Striking Force were about 115 miles (185 km) apart. Takagi ordered his ships to turn on their searchlights to help guide the 18 surviving aircraft back, and these aircraft had been recovered by 22.00.
Meanwhile, at 15.18 and 17.18 Neosho was able to radio TF17 that she was drifting to the north-west in sinking condition. Neosho's 17.18 report gave wrong co-ordinates, however, and this hampered subsequent US efforts to locate and rescue the sinking oiler. More significantly, at the tactical level the news informed Fletcher that his only nearby available fuel supply was no longer available.
As the fall of night ended aircraft operations for the day, Fletcher ordered TF17 to steam to the west and prepared to launch a 360° search at dawn. Crace also turned to the west to remain within striking range of the Louisiade islands group. Inoue directed Takagi to make sure he destroyed the US carriers on the following day, and postponed the 'Mo' (ii) landings to 12 May. Takagi decided to take his carriers 140 miles (225 km) to the north during the night so he could focus his morning search to the west and south and ensure that his carriers could provide better protection for the invasion convoy. Goto and Kajioka were unable to position and co-ordinate their ships in time to attempt a night attack on the Allied warships.
Each side expected to find the other early on the following day, and spent the night preparing its attack aircraft for the anticipated battle as their exhausted aircrews attempted to get a few hours sleep.
At 06.15 on 8 May, from a position 115 miles (185 km) to the east of Rossel island), Hara launched seven torpedo bombers to search the area in an arc between south-east and south-west, to a radius of 290 miles (465 km). The search was aided by three H6K flying boats from Tulagi and four G4M bombers from Rabaul. At 07.00, the carrier aircraft turned to the south-west and were joined by two of Goto’s cruisers, Kinugasa and Furutaka, for additional screening support. The invasion convoy, in the form of Goto’s Carrier Striking Force and Kajioka’s Port Moresby Invasion Group, steamed toward a rendezvous point 44 miles (72.5 km) to the east of Woodlark island to await the outcome of the carrier battle. During the night, the warm frontal zone. whose low-hanging clouds had helped to conceal the position of the US carriers on 7 May, moved away to the north and east, and now covered the Japanese carriers, limiting visibility to between 2.5 and 17 miles (3.25 and 27.5 km).
At 06.35, under Fitch’s tactical command and located about 210 miles (340 km) to the south-east of the Louisiade islands group, launched 18 SBD aircraft to undertake a 360° search out to a radius of 230 miles (370 km). The skies over the US carriers were generally clear at this time, with 20-mile (32-km) visibility.
At 08.20, one of Lexington's SBD aircraft sighted the Japanese carriers through a hole in the clouds and notified TF17, and a mere two minutes later, one of Shokaku's search aircraft sighted TF17 and notified Hara. At this moment the two forces were about 240 miles (385 km) apart, and each raced to launch its attack aircraft.
At 09.15, the Japanese carriers launched an attack force of 18 fighters, 33 dive-bombers and 18 torpedo bombers under the command of Lieutenant Commander Kakuichi Takahashi. The two US carriers each launched a separate attack force. On its way by 09.15, Yorktown's group comprised six fighters, 24 dive-bombers and nine torpedo bombers and was on its way, and by 09.25 Lexington's group of nine fighters, 15 dive-bombers and 12 torpedo bombers was also in the air. Both the Japanese and US carrier forces turned to head directly for each other’s estimated location at high speed in order to shorten the distance their aircraft would have to fly on their return legs.
Yorktown's dive-bombers reached the area of the Japanese carriers at 10.32, and then paused to allow the slower torpedo bomber squadron to arrive so that the two types of attack warplane could attack simultaneously. At this time, Shokaku and Zuikaku were about 10,000 yards (9145 m) apart, with Zuikaku hidden under a squall of low-hanging rain clouds. The two carriers were protected by a combat air patrol of 16 A6M fighters. Yorktown's dive-bombers began their attacks at 10.57 on Shokaku and hit the manoeuvring carrier with two 1,000-lb (454-kg) bombs, tearing open the forecastle and causing heavy damage to the carrier’s flight and hangar decks. Yorktown's torpedo bombers missed with all of their ordnance. Two US dive-bombers and two Japanese fighters were shot down during the attack.
Lexington's aircraft arrived over the Japanese carriers and attacked at 11.30. Two dive-bombers attacked Shokaku, hitting the carrier with one 1,000-lb (454-kg) bomb and inflicting additional damage. Two other dive-bombers descended on Zuikaku but missed with their bombs. Adversely affected by heavy cloud, the rest of Lexington's dive-bombers failed to locate the Japanese carriers. Lexington's torpedo bombers missed Shokaku with all 11 of their torpedoes. The 13 A6M fighters on patrol at this time shot down three F4M fighters.
With her flight deck heavily damaged and 223 of her crew killed or wounded, Shokaku could undertake no further aircraft operations, and at her captain’s request, Hara and Takagi authorised the damaged carrier’s retirement from the battle. Escorted by two destroyers, Shokaku pulled back to the north-east at 12.10.
At 10.55, Lexington's air-search radar detected the Japanese inbound aircraft at a range of 78 miles (125.5 km) and ordered nine F4F fighters to intercept. Expecting the Japanese torpedo bombers to be at a much lower altitude than they actually were, six of the F4M fighters were stationed too low, and thus missed the Japanese aircraft as they passed by overhead.
As a result of their heavy aircraft losses during the preceding night, the Japanese could not execute a full torpedo attack on both US carriers. Lieutenant Commander Shigekazu Shimazaki, commanding the Japanese torpedo bombers, ordered 14 of his aircraft to attack Lexington and four to attack Yorktown. An F4F shot down one of the Japanese aircraft, and eight patrolling SBD aircraft from Yorktown shot down three more as the Japanese torpedo bombers lost altitude to assume their attack position. Four SBD aircraft were shot down by A6M fighters escorting the torpedo bombers.
The Japanese attack began at 11.13 as the two carriers, some 3,000 yards (2745 m) apart, and their escorts opened fire with their anti-aircraft guns. The four torpedo planes which attacked Yorktown all missed, but the other formation made a pincer attack on Lexington, which had a considerably greater turning radius than Yorktown, and at 11.20 hit her with two 2,061-lb (935-kg) Type 91 torpedoes. The detonation of the first 17.7-in (450-mm) torpedo’s 529-lb (240-kg) HE warhead buckled the port aviation fuel stowage tanks, and undetected fuel vapour spread into surrounding compartments. The second torpedo ruptured the port water main, reducing water pressure to the carrier’s three forward fire rooms and making it necessary to shut down the associated boilers. Even so, the ship could still reach 24 kt on her remaining boilers. Four of the Japanese torpedo bombers were shot down by anti-aircraft fire.
The 33 Japanese dive-bombers circled to attack from upwind, and thus did not begin their attacks from 14,110 ft (4300 m) until three to four minutes after the torpedo bombers had begun their attacks. Shokaku's 19 dive-bombers lined up on Lexington and the other 14 targeted Yorktown. Escorting A6M fighters shielded the aircraft targeting Lexington from the carriers combat air patrol of four F4F fighters which attempted to intervene, but two F4F fighters circling above Yorktown were able to disrupt the Japanese formation targeting this carrier. The 19-aeroplane attack damaged Lexington with two bomb hits and several near misses, causing fires which had been contained by 12.33. At 11.27 Yorktown was hit in the centre of her flight deck by a single 551-lb (250-kg) semi-armour-piercing bomb: this penetrated four decks before exploding, causing severe structural damage to an aviation storage room, and killing or seriously wounding 66 men. Up to 12 near misses damaged Yorktown's hull below the waterline. Two of the dive-bombers were shot down by an F4M during the attack.
As the Japanese aircraft completed their attacks and began to withdraw, confident in their belief that they inflicted fatal damage to both carriers, they ran a gauntlet of F4M and SBD aircraft, and in the air battle which followed the USA lost three SBD and three F4F aircraft, and the Japanese three B5N, one D3A and one A6M.
By 12.00 the US and Japanese strike groups were on their way back to their respective carriers. During their return, aircraft from the two adversaries passed each other in the air, resulting in more combats.
The attack forces, each including many damaged aircraft, reached and landed on their respective carriers between 12.50 and 14.30. In spite of the damage they had suffered, Yorktown and Lexington were both able to recover aircraft from their returning air groups. During recovery operations, for various reasons the US carriers lost another five SBD, two TBD and one F4F aircraft, and the Japanese carrier lost two A6M, five D3A and one B5N aircraft. Forty-six of the Japanese attack force’s original 69 aircraft returned from the mission and landed on Zuikaku. Of these, three A6M, four D3A and five B5N aircraft were deemed damaged beyond repair and were immediately jettisoned.
As TF17 was recovering its aircraft, Fletcher assessed the situation. The returning crews reported that they had severely damaged one carrier, but that another had escaped damage. Fletcher noted that both his carriers were hurt and that his air groups had suffered high losses in their fighter complements. Fuel was also a concern as a result of Neosho's loss. At 14.22, Fitch notified Fletcher that he had reports of two undamaged Japanese carriers and that this was supported by radio intercepts. Believing that he faced overwhelming Japanese carrier superiority, Fletcher elected to withdraw TF17 from the battle, and radioed MacArthur the approximate position of the Japanese carriers with the suggestion of an attack with land-based bombers.
At about 14.30, Hara informed Takagi that only 24 A6M, eight D3A and four B5N carrierborne aircraft were currently operational. This was of great concern to Takagi, who was also worried about his ships' fuel levels: the cruisers were at 50% and some of his destroyers were as low as 20%. At 15.00, Takagi notified Inoue that his aircrews had sunk two US carriers (Yorktown and one 'Saratoga' class ship), but added that heavy losses in aircraft meant he could not continue to provide air cover for the invasion. Inoue, whose reconnaissance aircraft had sighted Crace’s ships earlier in the same day, recalled the invasion convoy to Rabaul, postponed 'Mo' (ii) to 3 July, and ordered his forces to assemble to the north-east of the Solomon islands group to begin the 'Ry' operation to take Nauru and Ocean islands. Zuikaku and her escorts headed toward Rabaul, and Shokaku steamed toward Japan and a programme of extensive repairs.
On Lexington, damage-control parties put out the fires and restored the carrier to operational condition, but at 12.47 sparks from unattended electric motors ignited aircraft fuel vapour near the ship’s central control station: the resulting explosion killed 25 men and started a large fire. At about 14.42 there was another large explosion, and this started a second severe fire. A third explosion took place at 15.25, and at 15.38 the ship’s crew reported that they could not control the fires. Lexington's crew started to abandon ship at 17.07. After the recovery of the carrier’s survivors, who included Fitch and the carrier’s captain, Frederick C. Sherman, at 19.15 the destroyer Phelps fired five torpedoes into the burning ship, which sank in 14,400 ft (4390 m) of water at 19.52 taking with her 216 of the carrier’s crew of 2,951 men, and 36 aircraft. Phelps and the other assisting warships left immediately to rejoin Yorktown and her escorts, which departed at 16.01 as TF17 retired to the south-west. Later in the evening of the same day, MacArthur informed Fletcher that eight of his B-17 bombers had attacked the invasion convoy, which was now retiring to the north-west.
During the same evening, Crace detached Hobart, which was critically short of fuel, and the destroyer Walke, which was having engine problems, to proceed to Townsville in north-eastern Australia. Crace overheard radio reports saying that the Japanese invasion convoy had turned back but, unaware of the fact that TF17 had withdrawn, remained on patrol with the rest of TG17.3 in the Coral Sea in case the Japanese invasion force resumed its advance towards Port Moresby.
On 9 May, TF17 altered course to the south-east and headed out of the Coral Sea via a route to the south of New Caledonia. Nimitz ordered Fletcher to return Yorktown to Pearl Harbor as soon as possible after refuelling at Tongatabu. During the day, USAAF bombers attacked Deboyne island and Kamikawa Maru, inflicting unknown damage. Having heard nothing from Fletcher, Crace now deduced that TF17 had departed the area and at 01.00 on 10 May, hearing no further reports of Japanese ships advancing toward Port Moresby, TG17.3 turned toward Australia and arrived at Cid Harbor, 150 miles (240 km) to the south of Townsville, on 11 May.
At 22.00 on 8 May, Yamamoto had ordered Inoue to turn his forces round and resume the offensive, destroy the remaining Allied warships, and complete the invasion of Port Moresby. Inoue did not cancel the recall of the invasion convoy, but ordered Takagi and Goto to pursue the remaining Allied warship forces in the Coral Sea. Critically short of fuel, Takagi’s ships spent most of 9 May refuelling from the fleet oiler Toho Maru. Late in the evening of 9 May, Takagi and Goto headed to the south-east and then to the south-west into the Coral Sea. Seaplanes from Deboyne island assisted Takagi in searching for TF17 on the morning of 10 May, but Fletcher’s and Crace’s forces were already well on their way out of the area. At 13.00 on 10 May, Takagi came to the conclusion that the Allied forces had departed and decided to turn back toward Rabaul. Yamamoto now concurred with Takagi’s decision and ordered the return of Zuikaku to Japan so that her air group could be rebuilt. At the same time, Kamikawa Maru collected her shore parties and departed Deboyne island. At about 12.00 on 11 May, a US Navy PBY flying boat on patrol from Nouméa sighted the drifting Neosho, and the US destroyer Henley arrived to rescued 123 survivors (14 of them from Sims) later in the day and then sent the oiler to the bottom with torpedoes.
Meanwhile Halsey’s TF16 reached the South Pacific near Efate in the New Hebrides islands group and, on 13 May, headed north to contest the approach of 'Ry' to Nauru and Ocean islands. After receiving intelligence about the Combined Fleet's forthcoming 'Mi' (ii) operation against Midway, on 14 May Nimitz ordered Halsey to make sure that Japanese reconnaissance aircraft sighted his ships on the following day and then return to Pearl Harbor immediately. At 10.15 on 15 May, a Kawanishi flying boat from Tulagi island sighted TF16 about 510 miles (820 km) to the east of the Solomon islands group: Halsey’s feint had worked. Fearing an attack by carrierborne aircraft on his exposed invasion forces, Inoue immediately cancelled 'Ry' and ordered his ships to return to Rabaul and Truk. On 19 May, after refuelling at Efate, TF16 turned toward Pearl Harbor, which it reached on 26 May. Yorktown arrived at Pearl Harbor on the following day.
Shokaku reached Kure in the Japanese home islands on 17 May after nearly capsizing in a storm as a result of her battle damage. Zuikaku arrived at Kure on 21 May after making a brief stop at Truk atoll on 15 May. Acting on signals intelligence, the US placed eight submarines along the projected route of the carriers' return paths to Japan, but the submarines were not able to make any attacks. The Japanese naval general staff estimated that it would take two to three months to repair Shokaku and to replenish the carriers' air groups, so neither of the carriers would be be able to participate in 'Mi' (ii). The two carriers rejoined the Combined Fleet on 14 July.
The five 'I' submarines supporting the 'Mo' (ii) undertaking were retasked to support an attack on Sydney Harbour three weeks later as part of a campaign to disrupt Allied supply lines. En route to Truk, however, I-28 was torpedoed on 17 May by the US submarine Tautog and went down with all hands.
The Battle of the Coral Sea was history’s first naval engagement in which the participating warships neither sighted nor fired directly at each other. Instead, aircraft acted as the offensive artillery for the ships involved. Thus, the respective commanders were participating in an entirely new form of warfare, carrier-versus-carrier, with which neither had any experience. Because of the greater speed at which decisions had to be reached, the Japanese were at a disadvantage as Inoue was too distant at Rabaul for the effective realtime direction of his forces, whereas Fletcher was present with his carriers. Moreover, the Japanese admirals involved were often slow to communicate important information to each other.
Their greater experience allowed the Japanese carrier aircrews to perform better than those of the US Navy, and this to achieve greater results with an equivalent number of aircraft. The Japanese attack on the US carriers on 8 May was better co-ordinated than that of the US force on the Japanese carriers. The Japanese suffered considerably greater losses to their carrier aircrews, however, losing 90 men killed in the battle when the American losses were 35 men. The group of very skilled and experience carrier aircrews with which Japan had begun the war were, in effect, irreplaceable in even the medium term as a result of the limitations of its aircrew training programmes and its lack of a pool of experienced reserves or advanced training programmes for new airmen. The Battle of the Coral Sea began the trend which would result in the irreparable attrition of Japan’s veteran carrier aircrews by the end of October 1942.
While the Americans did not perform as well as had been expected, they did learn from their mistakes and make improvements to their carrier tactics and equipment in matters such as fighter tactics, attack co-ordination, the nature and quality of torpedo bombers, and defensive tactics in matters such as anti-aircraft fire, all of which paid dividends in later battles. Radar gave the US Navy a limited advantage in this battle, but its value to the service increased over time as radar technology improved and the Allies learned how to employ radar more effectively. The loss of Lexington paved the way to improved methods for containing aviation fuel and better damage control procedures. Co-ordination between the Allied land-based air forces and the US Navy was poor during the battle, but then improved over time.
Each side claimed victory after the battle. In terms of ships lost, the Japanese had won a tactical victory by sinking one US fleet carrier, one destroyer and one oiler totalling some 41,825 tons for their own loss of one light carrier, one destroyer and several smaller warships totalling some 19,000 tons sunk by the Americans. At the time Lexington represented one-quarter of the US carrier strength in the Pacific. The Japanese public was informed of the victory with a major overstatement of the US losses and understatement of their own losses.
In strategic terms, however, the Allies won the Battle of Midway because the seaborne invasion of Port Moresby was averted, lessening the threat to the supply lines between the USA and Australia. Although the withdrawal of Yorktown from the Coral Sea conceded the field at the tactical level, at the strategic level the Japanese were forced to abandon the operation which had led to the Battle of Coral Sea.
Moreover, the Battle of the Coral Sea marked the first occasion on which a Japanese invasion force turned back without achieving its objective, and this was a fact which greatly boosted Allied morale after a series of defeats by the Japanese during the first six months of the Pacific war. Port Moresby was vital to Allied strategy and its garrison could well have been overwhelmed by the experienced Japanese invasion troops. The US Navy, however, also exaggerated the damage it had inflicted on the Japanese, and this caused the press to treat the naval reports of the Battle of Midway with more caution.
The results of the battle had a substantial effect on each side’s strategic planning. Without a hold in New Guinea, the subsequent Allied advance, arduous though it was, would have been more difficult. For the Japanese the battle was seen merely as a short-term setback. The results of the battle confirmed the low opinion held by the Japanese of US fighting capability and supported their overconfident belief that future carrier operations against US carrier forces were assured of success.
One of the most significant results of the Battle of the Coral Sea battle was the loss of Shokaku and Zuikaku to Yamamoto for his planned showdown with the US carriers at Midway, and of Shoho which was to have been employed at Midway in a tactical role supporting the Japanese invasion force. The Japanese believed that they sank two carriers in the Coral Sea, but this still left at least two other US carriers, Enterprise and Hornet with which to help the defence of Midway. The aircraft complement of the US carriers was greater than that of their Japanese counterparts, which, when combined with the land-based aircraft at Midway, meant that the Combined Fleet no longer enjoyed a significant numerical air superiority over the Americans in the impending battle. In fact, the Americans would have three carriers with which to oppose Yamamoto at Midway as Yorktown remained operational despite the damage she suffered in the Battle of the Coral Sea, and the US Navy was able to patch her up sufficiently at Pearl Harbor between 27 and 30 May to allow participation in the battle. At Midway, Yorktown's aircraft played crucial roles in sinking two Japanese fleet carriers, and this carrier also effectively absorbed both Japanese aerial counterattacks at Midway which would otherwise have been directed at Enterprise and Hornet.
In striking contrast with the determined US efforts to employ their maximum possible strength at Midway, the Japanese seemed not even to have considered trying to include Zuikaku in the operation, and no real consideration was given to the possibility of combining Shokaku's surviving aircrews into Zuikaku's air group or of providing Zuikaku with replacement aircraft so she could join the rest of the Combined Fleet at Midway. Shokaku herself was unable to conduct further aircraft operations, with her flight deck severely damaged, and required almost three months of repair in Japan.
It is arguable that Yamamoto made a grievous error in weakening the Combined Fleet before the strategic 'Mi' (ii) by diverting one-third of his available fleet carrier strength to 'Mo' (ii), which was an undertaking of only secondary significance. Moreover, Yamamoto seems to have missed the other implications of the Battle of the Coral Sea: the unexpected appearance of US carriers in exactly the right place and at exactly the right time to contest the Japanese, and US Navy carrier aircrews demonstrating sufficient skill and determination to do significant damage to the Japanese carrier forces. These would be repeated at Midway, and as a result, Japan lost four fleet carriers, the core of her naval offensive forces, and thereby lost the strategic initiative in the Pacific war.
The Australians and US forces in Australia were initially disappointed with the outcome of the Battle of the Coral Sea, fearing that 'Mo' (ii) was merely the precursor to an invasion of the Australian mainland and that the setback to Japan was only temporary. At a meeting late in May, the Australian Advisory War Council described the result of the Battle of Coral Sea the as 'rather disappointing' given the fact that the Allies had advance notice of what the Japanese planned. MacArthur provided the Australian prime minister, John Curtin, with his assessment of the battle, in which he stated that 'all the elements that have produced disaster in the Western Pacific since the beginning of the war' were still present as Japanese forces could strike anywhere if supported by major elements of the Japanese navy.
Because of their severe carrierborne air arm losses in carriers in 'Mi' (ii), however, the Japanese were unable to support another attempt to invade Port Moresby from the sea, and this compelled Japan to attempt an overland seizure of Port Moresby. Japan began its land offensive along the Kokoda Trail on 21 July from Buna and Gona, but by this time the Allies had reinforced New Guinea with additional troops (primarily Australian) starting with Brigadier Walter E. Smith’s Australian 14th Brigade, which embarked at Townsville on 15 May. The strengthened Australian forces slowed, then eventually halted the Japanese advance towards Port Moresby in September 1942, and Allied forces also defeated the 'Re' attempt by the Japanese to take the Allied base at Milne Bay.
In the meantime, the Allies learned in July that the Japanese had begun building an airfield on Guadalcanal. Operating from this base the Japanese would be able to threaten the maritime lines of communication across the Pacific to Australia. To prevent this, the Americans chose Tulagi and nearby Guadalcanal as the targets of their first offensive. The failure of the Japanese to take Port Moresby, and their defeat at Midway, had the effect of dangling their base at Tulagi and Guadalcanal without effective protection from other Japanese bases. Tulagi and Guadalcanal was four hours flying time from Rabaul, the nearest large Japanese base. On 7 August 11,000 US Marines landed on Guadalcanal in 'Watchtower' and 3,000 US Marines landed on Tulagi and nearby islands in 'Ringbolt'. The Japanese troops on Tulagi and nearby islands were outnumbered and killed almost to the last man in the Battle of Tulagi and Gavutu-Tanambogo, while the US Marines on Guadalcanal captured an airfield under construction by the Japanese. This began the Guadalcanal and Solomon islands campaigns, which took the form of a series of combined-arms attritional battles between Allied and Japanese forces over the next year which, in tandem with the New Guinea campaign, eventually neutralised the Japanese defences in the South Pacific, inflicted irreparable losses on the Japanese military in general, and its navy in particular, and contributed significantly to the Allies' eventual victory over Japan.
The delay in the advance of Japanese forces also allowed the US Marine Corps to land on Funafuti atoll of the Ellice islands group on 2 October 1942, with a 'Seabee' naval construction battalion to build airfields on three of the atolls from which Consolidated B-24 Liberator heavy bombers of Major General Willis A. Hale’s US 7th AAF could operate. The atolls of the Ellice islands group were staging points in the US preparations for the Battles of Tarawa and of Makin, which began on 20 November 1943 with 'Longsuit' as 'Galvanic' was implemented.
More distant cover was provided by Goto’s Port Moresby Support Force, which was divided into the Close Support Force (light carrier Shoho with 12 Mitsubishi A6M Reisen 'Zero' fighters and nine Nakajima B5N 'Kate' bombers, and the destroyer Sazanami) and the more distant Cover Force, Main Body (heavy cruisers Aoba, Kako, Kinugasa and Furutaka), which was designed also to cover Rear Admiral Kiyohide Shima’s Tulagi Invasion Force (one transport, fleet destroyers Kikuzuki and Yuzuki, and minelayers Okinoshima and Koei Maru).
There was also a Submarine Force divided into two parts as the Patrol Group with I-21, I-22, I-24, I-28 and I-29, and the Raiding Group with Ro-33 and Ro-34.