The Battle of the Coral Sea, from 4 to 8 May 1942, was a major naval battle between the Imperial Japanese Navy (IJN) and naval and air forces of the United States and Australia. Taking place in the Pacific Theatre of World War II, the battle was the first naval action in which the opposing fleets neither sighted nor fired upon one another, attacking over the horizon from aircraft carriers instead. It was also the first military battle between aircraft carriers.
To strengthen their defensive position in the South Pacific, the Japanese decided to invade and occupy Port Moresby (in the Territory of Papua) and Tulagi (in the southeastern Solomon Islands). The plan, Operation Mo, involved several major units of Japan's Combined Fleet. Two fleet carriers and a light carrier were assigned to provide air cover for the invasion forces, under the overall command of Admiral Shigeyoshi Inoue. The US learned of the Japanese plan through signals intelligence and sent two US Navy carrier task forces and a joint Australian-American cruiser force to oppose the offensive, under the overall command of US Admiral Frank J. Fletcher.
On 3–4 May, Japanese forces invaded and occupied Tulagi, although several supporting warships were sunk or damaged in a surprise attack by the US carrier Yorktown. Alerted to the presence of enemy aircraft carriers, the Japanese fleet carriers advanced towards the Coral Sea to locate and destroy the Allied naval forces. On the evening of 6 May, the two carrier fleets closed to within 70 nmi (81 mi; 130 km) but did not detect each other in the darkness. The next day, both fleets launched airstrikes against what they thought were the enemy fleet carriers, but both sides actually attacked other targets. The US sank the Japanese light carrier Shōhō, and the Japanese sank the destroyer Sims, and damaged the fleet oiler Neosho. On 8 May, both sides finally located and attacked the other's fleet carriers, leaving the Japanese fleet carrier Shōkaku damaged, the US fleet carrier Yorktown damaged, and the Lexington so critically damaged she was later scuttled.
Both sides having suffered heavy aircraft losses and carriers sunk or damaged, the two forces disengaged and retired from the area. Because of the loss of carrier air cover, Inoue also recalled the Port Moresby invasion fleet. Although the battle was a tactical victory for the Japanese in terms of ships sunk, it has been described as a strategic victory for the Allies. The battle marked the first time since the start of the war that a major Japanese advance had been turned back. More important, the damage to Shōkaku and the aircraft losses of Zuikaku prevented both ships from participating in the Battle of Midway the following month.
Background
Japanese expansion
On 8 December 1941 (7 December US time), Japan declared war on the US and the British Empire, after Japanese forces attacked Malaya, Singapore and Hong Kong as well as the US naval base at Pearl Harbor. In launching this war, Japanese leaders sought to neutralize the US fleet, seize territory rich in natural resources, and obtain strategic military bases to defend their far-flung empire. In the words of the Imperial Japanese Navy (IJN) Combined Fleet's "Secret Order Number One", dated 1 November 1941, the goals of the initial Japanese campaigns in the impending war were to "[eject] British and American strength from the Netherlands Indies and the Philippines, [and] to establish a policy of autonomous self-sufficiency and economic independence."
To support these goals, during the first few months of 1942, besides Malaya, Japanese forces attacked and took control of the Philippines, Singapore, the Dutch East Indies, Wake Island, New Britain, the Gilbert Islands and Guam, inflicting heavy losses on opposing Allied land, naval and air forces. Japan planned to use these conquered territories to establish a perimeter defense for its empire from which it expected to employ attritional tactics to defeat or exhaust any Allied counterattacks.
Shortly after the war began, the Japanese Naval General Staff, under the leadership of Admiral Osami Nagano, recommended an invasion of Northern Australia to prevent Australia from being used as a base to threaten Japan's perimeter defenses in the South Pacific. The Imperial Japanese Army (IJA) rejected the recommendation, stating that it did not have the forces or shipping capacity available to conduct such an operation. At the same time, Vice Admiral Shigeyoshi Inoue, commander of the IJN's Fourth Fleet (also called the South Seas Force) which consisted of most of the naval units in the South Pacific area, advocated the occupation of Tulagi in the southeastern Solomon Islands and Port Moresby in New Guinea, which would put Northern Australia within range of Japanese land-based aircraft. Inoue believed the capture and control of these locations would provide greater security and defensive depth for the major Japanese base at Rabaul on New Britain. The navy's general staff and the IJA accepted Inoue's proposal and promoted further operations, using these locations as supporting bases, to seize New Caledonia, Fiji, and Samoa and thereby cut the supply and communication lines between Australia and the United States.
In April 1942, the army and navy developed a plan that was titled Operation MO. The plan called for Port Moresby to be invaded from the sea and secured by 10 May. The plan also included the seizure of Tulagi on 2–3 May, where the navy would establish a seaplane base for potential air operations against Allied territories and forces in the South Pacific and to provide a base for reconnaissance aircraft. Upon the completion of MO, the navy planned to initiate Operation RY, using ships released from MO, to seize Nauru and Ocean Island for their phosphate deposits on 15 May. Further operations against Fiji, Samoa and New Caledonia (Operation FS) were to be planned once MO and RY were completed. Because of a damaging air attack by Allied land- and carrier-based aircraft on Japanese naval forces invading the Lae-Salamaua area in New Guinea in March, Inoue requested Japan's Combined Fleet send carriers to provide air cover for MO. Inoue was especially worried about Allied bombers stationed at air bases in Townsville and Cooktown, Australia, beyond the range of his own bombers, based at Rabaul and Lae.
Admiral Isoroku Yamamoto, commander of the Combined Fleet, was concurrently planning an operation for June that he hoped would lure the US Navy's carriers, none of which had been damaged in the Pearl Harbor attack, into a decisive showdown in the central Pacific near Midway Atoll. In the meantime Yamamoto detached some of his large warships, including two fleet carriers, a light carrier, a cruiser division, and two destroyer divisions, to support MO, and placed Inoue in charge of the naval portion of the operation.
Allied response
Unknown to the Japanese, the US Navy, led by the Communication Security Section of the Office of Naval Communications, had for several years enjoyed increasing success with penetrating Japanese communication ciphers and codes. By March 1942, the US was able to decipher up to 15% of the IJN's Ro or Naval Codebook D code (called "JN-25B" by the US), which was used by the IJN for about half of its communications. By the end of April, the US was reading up to 85% of the signals broadcast in the Ro code.
In March 1942, the US first noticed mention of the MO operation in intercepted messages. On 5 April, the US intercepted an IJN message directing a carrier and other large warships to proceed to Inoue's area of operations. On 13 April, the British deciphered an IJN message informing Inoue that the Fifth Carrier Division, consisting of the fleet carriers Shōkaku and Zuikaku, was en route to his command from Formosa via the main IJN base at Truk. The British passed the message to the US, along with their conclusion that Port Moresby was the likely target of MO.
Admiral Chester W. Nimitz, the new commander of US forces in the Central Pacific, and his staff discussed the deciphered messages and agreed that the Japanese were likely initiating a major operation in the Southwest Pacific in early May with Port Moresby as the probable target. The Allies regarded Port Moresby as a key base for a planned counteroffensive, under General Douglas MacArthur, against Japanese forces in the South West Pacific area. Nimitz's staff also concluded that the Japanese operation might include carrier raids on Allied bases in Samoa and at Suva. Nimitz, after consultation with Admiral Ernest King, Commander in Chief of the United States Fleet, decided to contest the Japanese operation by sending all four of the Pacific Fleet's available aircraft carriers to the Coral Sea. By 27 April, further signals intelligence confirmed most of the details and targets of the MO and RY plans.
On 29 April, Nimitz issued orders that sent his four carriers and their supporting warships towards the Coral Sea. Task Force 17 (TF 17), commanded by Rear Admiral Fletcher and consisting of the carrier Yorktown, escorted by three cruisers and four destroyers and supported by a replenishment group of two oilers and two destroyers, was already in the South Pacific, having departed Tongatabu on 27 April en route to the Coral Sea. TF 11, commanded by Rear Admiral Aubrey Fitch and consisting of the carrier Lexington with two cruisers and five destroyers, was between Fiji and New Caledonia. TF 16, commanded by Vice Admiral William F. Halsey and including the carriers Enterprise and Hornet, had just returned to Pearl Harbor from the Doolittle Raid in the central Pacific. TF 16 immediately departed but would not reach the South Pacific in time to participate in the battle. Nimitz placed Fletcher in command of Allied naval forces in the South Pacific area until Halsey arrived with TF 16. Although the Coral Sea area was under MacArthur's command, Fletcher and Halsey were directed to continue to report to Nimitz while in the Coral Sea area, not to MacArthur.
Based on un-encrypted intercepted radio traffic from TF 16 as it returned to Pearl Harbor, the Japanese assumed that all but one of the US Navy's carriers were in the central Pacific. The Japanese did not know the location of the remaining carrier, but did not expect a US carrier response to MO until the operation was well under way.
Battle
Prelude
During late April, the Japanese submarines Ro-33 and Ro-34 reconnoitered the area where landings were planned. The submarines investigated Rossel Island and the Deboyne Group anchorage in the Louisiade Archipelago, Jomard Channel, and the route to Port Moresby from the east. They did not sight any Allied ships in the area and returned to Rabaul on 23 and 24 April respectively.
The Japanese Port Moresby Invasion Force, commanded by Rear Admiral Kōsō Abe, included 11 transport ships carrying about 5,000 soldiers from the IJA's South Seas Detachment plus about 500 troops from the 3rd Kure Special Naval Landing Force (SNLF). Escorting the transports was the Port Moresby Attack Force with one light cruiser and six relatively old Kamikaze and Mutsuki-class destroyers under the command of Rear Admiral Sadamichi Kajioka. Abe's ships departed Rabaul for the 840 nmi (970 mi; 1,560 km) trip to Port Moresby on 4 May and were joined by Kajioka's force the next day. The ships, proceeding at 8 kn (9.2 mph; 15 km/h), planned to transit the Jomard Channel in the Louisiades to pass around the southern tip of New Guinea to arrive at Port Moresby by 10 May. The Allied garrison at Port Moresby numbered around 5,333 men, but only half of these were infantry and all were badly equipped and undertrained.
The Tulagi invasion force, commanded by Rear Admiral Kiyohide Shima, consisted of two minelayers, two older Mutsuki-class destroyers, five minesweepers, two subchasers and a transport ship carrying about 400 troops from the 3rd Kure SNLF. Supporting the Tulagi force was the covering group with the light carrier Shōhō, the IJN's four Furutaka /Aoba-class heavy cruisers, and one destroyer, commanded by Rear Admiral Aritomo Gotō. A separate cover force (sometimes referred to as the support group), commanded by Rear Admiral Kuninori Marumo and consisting of two light cruisers, the seaplane tender Kamikawa Maru and three gunboats, joined the covering group in providing distant protection for the Tulagi invasion. Once Tulagi was secured on 3 or 4 May, the covering group and cover force were to reposition to help screen the Port Moresby invasion. Inoue directed the MO operation from the cruiser Kashima, with which he arrived at Rabaul from Truk on 4 May.
Gotō's force left Truk on 28 April, cut through the Solomons between Bougainville and Choiseul and took station near New Georgia Island. Marumo's support group sortied from New Ireland on 29 April headed for Thousand Ships Bay, Santa Isabel Island, to establish a seaplane base on 2 May to support the Tulagi assault. Shima's invasion force departed Rabaul on 30 April.
The Carrier Strike Force, consisting of the aircraft carriers Shōkaku and Zuikaku, the heavy cruisers Myōkō and Haguro, and the destroyers Shigure, Shiratsuyu, Ariake, Yūgure, Ushio, and Akebono sortied from Truk on 1 May. The strike force was commanded by Vice Admiral Takeo Takagi (flag on cruiser Myōkō), with Rear Admiral Chūichi Hara, on Zuikaku, in tactical command of the carrier air forces. The Carrier Strike Force was to proceed down the eastern side of the Solomon Islands and enter the Coral Sea south of Guadalcanal. Once in the Coral Sea, the carriers were to provide air cover for the invasion forces, eliminate Allied air power at Port Moresby, and intercept and destroy any Allied naval forces which entered the Coral Sea in response.
En route to the Coral Sea, Takagi's carriers were to deliver nine Zero fighter aircraft to Rabaul. Bad weather during two attempts to make the delivery on 2–3 May compelled the aircraft to return to the carriers, stationed 240 nmi (280 mi; 440 km) from Rabaul, and one of the Zeros was forced to ditch in the sea. In order to try to keep to the MO timetable, Takagi was forced to abandon the delivery mission after the second attempt and direct his force towards the Solomon Islands to refuel.