Until this battle, the Japanese advance into the Pacific had continued unabated. Japanese forces sought to take Port Moresby on the southern side of the large island of New Guinea. It was essential for the Japanese to control the approaches to Australia and thereby protect the large base that they had recently established at Rabaul on New Britain. Japanese strategy called for the establishment of a large defensive perimeter far out from the home islands. Eventually, Japan hoped to lure the remnants of the U.S. fleet into a climactic battle somewhere along its defensive ring of bases, where the Japanese fleet could rely on the additional impact of land-based aircraft.

Until this battle, the Japanese advance into the Pacific had continued unabated. Japanese forces sought to take Port Moresby on the southern side of the large island of New Guinea. It was essential for the Japanese to control the approaches to Australia and thereby protect the large base that they had recently established at Rabaul on New Britain. Japanese strategy called for the establishment of a large defensive perimeter far out from the home islands. Eventually, Japan hoped to lure the remnants of the U.S. fleet into a climactic battle somewhere along its defensive ring of bases, where the Japanese fleet could rely on the additional impact of land-based aircraft.

Japanese forces under the command of Vice Admiral Shigeyoshi Inouye launched an end run around western New Guinea by sending invasion forces to Port Moresby by sea. Some invasion forces were also intended to establish a seaplane base in the nearby Solomon Islands, and they took Tulagi in the Solomons on May 3. However, they ran into a U.S. naval ambush in the Coral Sea. ULTRA, the U.S. code-breaking operation, had deciphered most of the Japanese naval code, and U.S. intelligence had learned of Japan’s invasion plans. For the first time in naval history, surface ships from both fleets never saw each other during the battle. Fighting was carried out entirely by aircraft flying from three Japanese and two U.S. carriers that were approximately 175 miles apart. During the exchange of attacks on May 7 and 8, the Japanese lost one light carrier, the Shoho, and suffered damage on the larger Shokaku. The Americans, under the command of Rear Admiral Frank Fletcher, lost one of their two large carriers, the Lexington. The other carrier, the Yorktown, was damaged and had to limp to Pearl Harbor for repairs. Several other ships were sunk on both sides.

The U.S. aircraft carrier Lexington explodes after being hit by Japanese bombs during the Battle of the Coral Sea. The other large U.S. carrier in the battle, the Yorktown, was so badly damaged that it had to return to port for repairs. (AP/Wide World Photos)

Which side gained the victory was not clear at first. The Japanese had exchanged a small carrier for a large one, and when other losses are calculated, they won the tactical victory in terms of tonnage sunk. At the time, Japanese leaders boasted of having won a great victory, convinced that they had sunk both U.S. carriers. However, the battle was really a strategic victory for the United States. The Japanese invasion fleet, which had been steaming toward Port Moresby, turned back. This was the first time that a Japanese advance in the Pacific was prevented. Checked in the Battle of the Coral Sea, the Japanese began a campaign to take Port Moresby over land, which necessitated going up and over the spine of New Guinea, the Owen Stanley Range. The Australians were able to hold them back in a struggle fought in miserable terrain.

The U.S. Navy gained vital combat experience and a boost in morale from the battle, which demonstrated that the Japanese advance could be held up and turned back. The battle set the stage for the long series of land, sea, and air battles centering on the island of Guadalcanal in the Solomons. These battles were part of the Japanese plan to threaten Australia, an extension of Japanese power that met considerable resistance from the U.S. Navy. The battle also reduced Japanese strength available for the Battle of Midway: Two Japanese carriers were not available for the battle so American carriers could confront the Japanese fleet outnumbered by only four to three instead of six to three.