May 4-8, 1942 - The Battle of the Coral Sea.

In the first naval engagement of history fought without the opposing ships making contact, U.S. carrier forces stopped a Japanese attempt to land at Port Moresby by turning back the covering carrier force. In the battle, the Japanese lost the light carrier Shoho and the U.S. lost the carrier, USS Lexington (CV 2).

Just as the battle between the USS Monitor and the CSS Virginia (Merrimac) may be deemed a turning point in military history, the battle of the Coral Sea is a useful marker of the time when the way battles were fought changed forever.

For thousands of years, battles were fought between foes who could see each other. Indeed, the changeover from sword and bow to bayonet and gun changed little. The first muskets actually had less range and accuracy than the British longbow. Even canonfire between ships did not change the fact that foes could still see each other.

The Coral Sea changed this. Now battles were to be fought between foes beyond the visible horison. The aircraft became dominant over the line-of-battle ship in a way that even Pearl Harbor had not established.

Located between Australia, New Guinea, and the Solomon Islands, the Battle of the Coral Sea resulted in a tactical Japanese victory, but a strategic Allied victory.

Having conquered nearly all of Southeast Asia in just a few months, Japan was at the apex of its power. Still reeling from a long series of humiliating defeats, the Allies were just beginning to develop the skills and organise the material assets needed to survive and, eventually, strike back. Allied strategy at this time was focused on a defensive build-up of United States Army and Marine strength on New Caledonia (well to the south of the Solomon Islands), and Australian air and ground strength at Port Moresby (in southern New Guinea, just north of the Australian mainland).

In April 1942, Japanese forces left their stronghold of Rabaul (on New Britain, just north of New Guinea) and launched a two-pronged amphibious invasion of Port Moresby (Operation MO), and Tulagi in the Solomon Islands. The intention was threefold: to establish control of the Solomons, initially with a seaplane base; to destroy and then occupy Port Moresby (the last Allied base between Japan and Australia); and in doing these things, to bring the American aircraft carrier fleet to battle for the first time in the war.

Three Japanese fleets set sail: the invasion forces for the Solomons and Port Moresby, and a covering force consisting of two big new aircraft carriers (Shokaku and Zuikaku, both Pearl Harbor veterans), a smaller carrier (Shoho), two heavy cruisers, and supporting craft. Alerted by radio intercepts, the Allies knew that Japanese land-based aircraft were being moved south and that an operation was impending. In opposition, they had three main fleets: USS Yorktown (CV-5) already in the Coral Sea under the command of Admiral Frank Jack Fletcher, USS Lexington (CV-2) en route, and a joint Allied surface fleet. The carriers USS Hornet (CV-8) and USS Enterprise (CV-6) were heading south after the Doolittle Raid on Tokyo but arrived too late to take part in the battle.

Lexington arrived to join Yorktown on May 1st. The Japanese occupied Tulagi without incident on May 3rd, and construction of a seaplane base started. After fuelling, Yorktown closed on Tulagi and, on May 4, launched three successful strikes against Japanese shipping and aircraft there — revealing the presence of an American carrier to the enemy but sinking the destroyer Mikazuki, crippling the island's seaplane reconnaissance capability, and damaging other vessels before retiring to the south to rendezvous with Lexington and the newly-arrived cruisers. Meanwhile, the two large Japanese carriers were approaching from south of the Solomons — neatly placing the Allied fleet between the two Japanese fleets.

Land-based B-17s attacked the gradually approaching Port Moresby invasion fleet on May 6 with the usual lack of success. (Almost another year would pass before air forces realised that high-level bombing raids on moving naval targets were pointless.) Although both carrier fleets flew extensive searches on the 6th, cloudy weather kept them hidden from each other and the two fleets spent the night only 70 miles apart. Other allied aircraft joined the battle from airbases at Cooktown and Iron Range on Cape York Peninsula.

That night Fletcher, mindful that his primary role was to protect Port Moresby, took the difficult decision to detach the Allies' main surface fleet, under the Australian Rear Admiral John Crace, to block the probable course of an invasion fleet. Crace's force consisted of the cruisers HMAS Australia, USS Chicago (CA-29), HMAS Hobart, and the destroyers USS Perkins, USS Walke and USS Farragut. Fletcher and Crace knew that exposing surface ships to attack by land-based aircraft without air cover was to risk the same fate that had overtaken the British battleships HMS Prince of Wales and HMS Repulse five months before. Their fears were realised when the cruisers were located by a squadron of Japanese torpedo bombers and came under intense air attack, on the afternoon of May 7. Whether as a result of luck or skill, the Allied ships escaped with few casualties and little damage. Only a matter of minutes after the Japanese raid, Crace's force was inadvertently attacked by B-17s, and the Farragut and Perkins once again survived narrow misses.

On the 7th, both fleets flew off all available aircraft, but neither found the main body of the other, and both mistakenly attacked subsidiary forces. Japanese aircraft found and attacked the US fleet oiler USS Neosho (AO-23) and escorting destroyer USS Sims (DD-409), mistaking them for a carrier and a cruiser. The Sims was sunk while the Neosho was crippled. Meanwhile, the US aircraft had missed Shokaku and Zuikaku but found the invasion fleet, in company with the small carrier Shoho, which was soon sunk. In the previous five months, the Allies had lost a dozen battleships and carriers and been unable to sink a single major Japanese unit in return. Shoho was small by carrier standards, but the laconic "scratch one flattop" radioed back to Lexington brought news of the first Allied naval success of the Pacific war.

Finally, with dawn searches on May 8, the main carrier forces located one another and launched maximum effort raids, which passed each other in the air. Hidden by rain, Zuikaku escaped detection, but Shokaku was hit three times by bombs. Listing and on fire, Shokaku was unable to land her aircraft and effectively out of action.

Both American carriers were hit by the Japanese strike: Yorktown by a bomb, the larger, less maneuverable Lexington by both bombs and torpedoes. Although she survived the immediate damage and was thought to be repairable, leaking aviation fuel exploded a little over an hour later: Lexington had to be abandoned and torpedoed to prevent capture.

Crace's force continued to stand between the invasion force and Port Moresby. Inoue was misled by returning fliers' reports, as to the strength of the Allied cruiser-destroyer force, and ordered the invasion fleet to return. With Shokaku damaged and Zuikaku short on aircraft, neither was able to take part in the crucial Battle of Midway a month later. Yorktown returned to Pearl Harbor.

In tactical terms, the Japanese had had a narrow victory. One small carrier lost and a large carrier damaged, against the loss of a large carrier and equivalent damage to another. But from the Allied point of view, after five months of continuous defeat, a battle that came out almost even was close enough to a victory as not to matter. More importantly, the seabourne invasion of Port Moresby was averted. Moresby was vital to Allied strategy, and could not have been defended by the ground forces then stationed there. The loss of Port Moresby may well have meant the loss of Australia, and would certainly have been a dreadful blow to the Allied cause. Without a toehold in New Guinea, the subsequent Allied advance, difficult though it was, would have been much harder still. As a result of the Coral Sea battle, the Japanese were forced to attempt taking Moresby overland. The consequent delay was just long enough to permit the arrival of veteran AIF soldiers to fight the Kokoda Track campaign and the Battle of Milne Bay, which in turn relieved pressure on Guadalcanal.

Less directly but no less significantly, the loss of highly trained aircrew from the carriers was never to be made up. Although Zuikaku was only slightly damaged, with only 40 aircraft left she was in no condition to fight and had to return to Japan to replenish. Shokaku took six months to repair. Neither carrier was able to take part in the crucial battle of Midway — a very close-fought encounter that either carrier may have been able to turn. Prior to the battles of the Coral Sea and Midway, Japanese naval aviation was unchallengeable in two oceans. Long years of hard peace-time training, and real-life exercises against the hapless Chinese had honed an elite group of flyers. Japan could manufacture plenty of replacement aircraft, and at least a few replacement carriers, but could not replace the most skilled naval pilots in the world. From this time on, Japanese naval aviation began to decline.