Semaphore: Sea Control and the Battle of the Coral Sea

Semaphore Issue 1, 2012
Semaphore Issue 1, 2012

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Fought between 4 and 8 May 1942, the Battle of the Coral Sea is widely recognised as the first encounter between fleets in which the surface forces did not sight one another and the only offensive weapons were aircraft. More than this, however, the battle was the single most important event in shaping the course of the subsequent campaigns in New Guinea and the South-West Pacific. Key to an understanding of the battle’s continuing significance is the fact that although the Japanese sustained relatively smaller losses, their forces failed to achieve the degree of sea control necessary to operate successfully south of New Guinea. They were thus thwarted in their ultimate aim, a direct amphibious assault on Port Moresby.

By early 1942, the Japanese appeared triumphant on all fronts. Their disorganised opponents had been overwhelmed by the Imperial Japanese Navy’s use of maritime manoeuvre to achieve surprise, local superiority and rapid advance. Yet the unexpected swiftness of their conquests also brought challenges to Japanese military planners. “What are we going to do...?” mused the Combined Fleet’s Chief of Staff, Rear Admiral Ugaki, on 5 January, “Advance to Australia, to India, attack Hawaii, or destroy the Soviet Union…?”[1] The Japanese predicament was that to consolidate the areas already held they needed to move their ‘interception zones’ continuously forward; neutralising enemy bases within reach of their own and thereby making it ever more difficult for the Allies to mount a successful counter-offensive. Hence, by capturing Rabaul on 23 January, the Japanese had provided defence-in-depth for their naval headquarters at Truk, 700 miles to the north in the Caroline Islands. But, having secured Rabaul, they then had to consider its defence from air strikes and amphibious assaults launched from Port Moresby on Papua’s southern shores.

Discussions at Japanese Imperial General Headquarters thereafter sought to determine how best to extend operations, and thereby create a ‘final line of offence’. The more daring among the Naval Staff suggested continuing south to invade Australia. But the Army would have none of it, calculating that Australia’s conquest would require at least twelve divisions. Not only could these troops not be spared from the China war, but the 1.5 million tons of shipping needed to transport them was already earmarked to bring newly acquired raw materials back to Japan. Arguments over the benefits of moving east, south or west continued for several weeks. The Army would have preferred to maintain a defensive strategy in the south, but did not ultimately oppose the Navy’s desire to establish protected forward bases in key areas of the South Pacific. Lae and Salamaua on the northeastern coast of Papua were to be the initial objectives, to be followed at an appropriate time by Tulagi in the southern Solomons and then the Port Moresby ‘if at all possible’. [2] With these objectives properly garrisoned, and airfields operating at each, the Japanese Navy expected to control the seas north of Australia while simultaneously using its submarines to deny Allied supply lines through the Indian and Pacific oceans.

Lae and Salamaua succumbed to amphibious assaults on 8 March. Minor landings were also made on the north coast of Bougainville at month’s end, but the Japanese made no further offensive moves until an extension of their war plans in April. The most important factor behind this hiatus was the realisation that a Port Moresby assault required a more measured approach. Essential to the safe transfer of troops and materiel across the enormous Pacific distances was to maintain control of the sea, including the airspace above it. From early February 1942 it became increasingly difficult for the Japanese to ignore Allied air attacks on Rabaul and other advanced bases mounted both from US Navy carrier task forces and airfields in Darwin and north Queensland.

The American aircraft carriers, which had fortuitously survived the Pearl Harbor debacle, proved a particular complication. Their mobility made the timing and direction of an attack impossible to predict, and air strikes against the Japanese Fourth Fleet had already succeeded in delaying the Lae-Salamaua invasion. Although not yet critical to Japanese planning, the damage inflicted highlighted the futility of attempting further amphibious movements without sufficient air defence; the more so since an assault on Port Moresby required a sea passage of more than 600 miles, half of which would be through the Coral Sea within easy reach of Australian airfields. Designated for the invasion was the 5000-strong South Seas Force, and its commander, Major General Tomitaro Horii, requested a strengthening of land-based air units and additions to the air strength of the Fourth Fleet, which at the time consisted only of the small carrier Shoho.

The Japanese Combined Fleet determined just two fleet carriers, Shokaku and Zuikaku, could be spared for the Port Moresby operation. Although, since the mobile carrier fleet was currently employed in the Indian Ocean, these would not be available until late April. In the interim, debate on future plans continued. Of central importance was to bring forward the ‘decisive battle’ against the US Pacific Fleet that had long been at the heart of Japanese naval doctrine. A major ‘Eastern Operation’, with its aim the occupation of Midway Island at the western end of the Hawaiian chain, was something the Americans could not ignore, and therefore became a priority. But, in addition to securing the Port Moresby airfields there would now be an amphibious advance through the Solomon Islands and thence to New Caledonia, the New Hebrides, Fiji and Samoa. Submarine operations were proving less decisive than expected, but the Navy remained confident that a southern thrust would cut sea communications across the Pacific, rendering Australia strategically irrelevant and preventing its build-up as the primary Allied support base.

Japanese overconfidence meant that the critical flaws in these plans went either unnoticed or ignored. Fundamentally, commanders did not appreciate the need to consider all dimensions of Japan’s maritime position, and their forces had nothing like sufficient capability to undertake such a dispersed and continuous series of campaigns. That the Port Moresby operation had to await the return of the carriers from the Indian Ocean, and was in turn timed to allow forces to be reconstituted before the Midway invasion, gives more than a hint of Japanese naval limitations. Yet similar deficiencies existed in many other aspects of their force structure; an inadequate supply of transports being the most critical. Not surprisingly, logistics became an ongoing Japanese anxiety, and a weakness that could only worsen as the war lengthened and Allied interdiction campaigns took their toll. As early as 20 March, General Horii openly expressed his grave concerns over the ability to maintain supply to Port Moresby after an initial assault.

Imperial Headquarters wanted Port Moresby taken by 10 May and the Fourth Fleet commander, Vice Admiral Shigeyoshi Inoue, directed the sailing of the various formations from Truk and Rabaul from 29 April. Japanese naval operations tended towards over complexity, and in addition to the Port Moresby and Tulagi landing groups, each with their own support force of cruisers and destroyers, Inoue also deployed a separate Main Body Support Force based on Shoho, and a Carrier Striking Force comprising Shokaku and Zuikaku under Vice Admiral Takagi. Landings at Tulagi began on 3 May.

Fortunately, Allied commanders were not unaware of these movements. Decrypted intercepts of Japanese radio communications provided a priceless advantage throughout the war, and on this occasion sufficient warning to allow an effective response. As a counter, Admiral Chester Nimitz, Commander-in-Chief of the US Pacific Fleet, ordered the Yorktown and Lexington carrier task groups to rendezvous off the New Hebrides under the tactical command of Rear Admiral Frank Fletcher. Also joining was a combined Australian-American formation, consisting of three cruisers and a destroyer commanded by the Australian squadron commander, Rear Admiral Jack Crace. By 2 May Fletcher was already pre-positioning his forces to intercept the Japanese.

The opening of the Battle of the Coral Sea is generally marked from 4 May when Yorktown’s aircraft carried out a successful strike against Japanese invasion shipping at Tulagi. The raid confirmed the presence of a US carrier task force in the region, but with Admiral Inoue still confident in his own air strength the Port Moresby invasion force proceeded as planned. Thereafter, each of the opposing carrier forces began the deliberate process of attempting to find the other and get in the first blow. At one stage the groups were just 70 miles apart, but bad weather meant that confusing reports came in to both commanders, and the exact strength and disposition of the enemy remained uncertain throughout.

On the morning of 7 May Fletcher detached Crace’s formation, and ordered it to the northwest to block any Japanese shipping attempting to enter the Coral Sea through the Jomard Passage between the tail of New Guinea and the Louisiade archipelago. Crace arrived in position in the early afternoon and immediately began his patrol. His ships had been under enemy observation during their passage, and within the hour the Japanese began their attack. Without air cover Crace’s situation was parlous, but good defence tactics resulted in at least five aircraft destroyed and skilful ship handling allowed the enemy no hits. Nevertheless, on their return to Rabaul the Japanese airmen incorrectly reported the sinking of one battleship and damage to another. Trusting the report, Inoue saw no need to launch further strikes on Crace, but he did order the invasion convoy to reverse course while he attempted to clarify the situation with regard to the ‘battleship’ sightings and the position of the US carriers.

HMAS Australia (II) under Japanese attack at the Battle of the Coral Sea. One bomber lies burning astern. (SPC-A)
HMAS Australia (II) under Japanese attack at the Battle of the Coral Sea. One bomber lies burning astern. (SPC-A)

Neither the Japanese nor the US carrier forces made contact with their enemy’s main strength on 7 May. They did discover smaller formations however, and a redirected strike from both American carriers found Shoho without air cover and sank her in minutes. For their part, Japanese carrier aircraft managed to find and sink a US tanker and destroyer. Heavy cloud and confused reporting prevented any further encounters until the following day, but in the ensuing engagements Shokaku was badly hit and Zuikaku lost heavily in aircraft and crews. Crucial to future events in the central Pacific, neither carrier was subsequently available for the Midway operation. On the American side, Lexington received crippling damage and was eventually sunk by an escorting destroyer.

Both fleets were too battered to continue the fight, but the Japanese laboured under the greater strategic impact. With his organic air power greatly reduced, Inoue decided not to persist with the Port Moresby invasion. More importantly, the Japanese thereafter developed a marked reluctance to risk their surface forces south of Papua. In consequence, Allied shipping continued to run largely unmolested to New Guinea, while the Japanese determined that Port Moresby’s capture must be accomplished by crossing the mountain ranges from the northern coast. The shape of the future campaign was thus resolved, much to the Allies’ advantage.

Achieving sea control allows a force the freedom of action to use an area of sea for its own purposes for a period of time, and if required deny the sea’s use to an opponent.[3] It remains one of the most important tasks of maritime forces and is fundamental to the success of any maritime campaign. The Battle of the Coral Sea, the first stemming of the Japanese tide in the South-West Pacific, serves as an enduring reminder of sea control’s importance in any considerations of future Australian security.

  1. DM Goldstein & KV Dillon (eds), Fading Victory: The Diary of Admiral Matome Ugaki, University of Pittsburgh Press, Pittsburgh, 1991, p. 68.
  2. S Bullard (translator), Japanese Army Operations in the South Pacific Area: New Britain and Papua campaigns, 1942-43, Australian War Memorial, Canberra, 2007, p. 56.
  3. Royal Australian Navy, Australian Maritime Doctrine, Sea Power Centre - Australia, Canberra, 2010, p. 72.

Sea Power Centre - Australia

Sea Power Centre - Australia
Department of Defence
Canberra ACT 2600