Japan’s initial war plans were now realized, but the Allies showed no signs of interest in peace negotiations. In fact, it seemed clear that an Allied counterstroke was imminent. Small carrier task forces of the U.S. Pacific Fleet hit the Marshalls on February 1, 1942, Wake on February 23, and Marcus Island on March 1. Land-based bombers from the south struck Rabaul on February 23. It was also clear that the Allies were establishing bases in Australia for future counteroffensives and were developing a well-protected line of communications across the South Pacific to these bases. The Japanese therefore decided to expand their perimeter and to cut the line of communications to Australia. Pushing down the Solomons from Rabaul, they planned to occupy New Caledonia, Fiji, and Samoa. To protect their flanks, they would seize eastern New Guinea and the western part of New Britain, threatening Australia from an air base to be established at Port Moresby in southeastern New Guinea. They also planned to capture Midway Island and to establish air bases in the Aleutians.

On February 10, 1942, the Japanese occupied Gasmata, in western New Britain. They seized Lae and Salamaua in eastern New Guinea on March 8 and made their first landings in the Solomons, at Buka, five days later. They occupied nearby Bougainville in early April and landed almost simultaneously in the Admiralty Islands to ensure their complete control over the Bismarck Archipelago. Except for several ships sunk or damaged in a raid by U.S. carrier-based planes during the Lae-Salamaua landings, the Japanese encountered no serious opposition to these moves. They at once began developing bases to support future advances. Far to the west, meanwhile, to gain control of the Indian Ocean and further to isolate Australia, Japanese forces seized the Andaman Islands on March 23, 1942. During the first week of April, Japanese carrier-based aircraft and submarines preyed on British warships and merchantmen in the Indian Ocean and Bay of Bengal, crippling the British Eastern Fleet, sinking nearly 30 cargo ships, and heavily damaging shore installations in Ceylon (now Sri Lanka).

The Allies’ reorganization

By now the U.S.-British combined chiefs of staff had decided to establish a new command structure in the Pacific. The entire area was placed under the strategic direction of the U.S. Joint Chiefs, who divided it into two major theatres. They appointed MacArthur supreme commander, Southwest Pacific Area, which included the Dutch East Indies (less Sumatra), the Philippines, Australia, the Bismarck Archipelago, and the Solomons. Adm. Chester W. Nimitz (USN) became commander in chief, Pacific Ocean Areas, which included most of the rest of the Pacific not under MacArthur. MacArthur and Nimitz assumed their commands in mid-April and early May. Their missions were practically identical: to hold the line of communications between the United States and Australia; to contain the Japanese within the Pacific; to support the defense of North America; and to prepare for major amphibious counteroffensives.

The Japanese suffered a serious psychological blow on April 18, 1942, when 16 U.S. Army B-25 bombers under Lieut. Col. James H. Doolittle attacked Tokyo from the U.S. carrier Hornet. The raid caused little damage, but boosted Allied morale, caused the Japanese government to lose considerable face, pinned down Japanese fighter planes on home fields, and accelerated Japanese plans for extending their perimeter.

The Battles of the Coral Sea and Midway

By the end of April 1942 the Japanese were ready to assert control of the Coral Sea (between Australia and New Caledonia) by establishing air bases at Port Moresby in southeastern New Guinea and at Tulagi in the southern Solomons. Allied intelligence learned of the Japanese plan to seize Port Moresby from the sea and alerted all available sea and air power. When the Japanese landed at Tulagi on May 3, carrier-based U.S. planes from a task force commanded by Rear Adm. Frank J. Fletcher struck the landing group, sinking one destroyer and some minesweepers and landing barges. Most of the naval units covering the main Japanese invasion force which left Rabaul for Port Moresby on May 4 took a circuitous route to the east which invited a clash with Fletcher’s forces.

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On May 5 and 6, 1942, the opposing carrier groups sought each other, and on the morning of May 7, Japanese carrier-based planes sank a U.S. destroyer and an oiler. Fletcher’s planes sank the light carrier Shoho and a cruiser. The next day Japanese aircraft sank the U.S. carrier Lexington and damaged the carrier Yorktown, while U.S. planes so crippled the large Japanese carrier Shokaku that it had to retire from action. So many Japanese planes were lost that the Port Moresby invasion force, without adequate air cover and harassed by Allied land-based bombers, turned back to Rabaul. While the four-day engagement, designated the Battle of the Coral Sea, was a tactical victory for the Japanese, it was a strategic victory for the Allies, whose naval forces, employing only aircraft and never closing within gunshot range of Japanese vessels, had saved Port Moresby.

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Despite this setback, the Japanese continued with plans to seize Midway Island and bases in the Aleutians. Seeking a naval showdown, they sent out, along with invasion forces for those objectives, the bulk of their fleet: 4 heavy and 3 light carriers, 2 seaplane carriers, 11 battleships, 15 cruisers, 44 destroyers, 15 submarines, and various support and escort vessels. U.S. cryptanalysts however, had cracked the Japanese naval code and divined Japanese intentions, an intelligence coup that would prove decisive in the battle’s outcome. The U.S. Pacific Fleet mustered 3 heavy carriers, 8 cruisers, 18 destroyers, and 19 submarines; whereas the Japanese had no land-based air support, the Americans could commit about 115 Navy, Marine Corps, and Army planes from Midway and Hawaii.

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The Battle of Midway began on June 3, 1942, when U.S. bombers struck ineffectually at Japanese ships about 500 miles (800 km) west of Midway Island. Early the next morning Japanese planes attacked Midway heavily, while Japanese ships again escaped damage from U.S. land-based planes. U.S. carrier-based aircraft struck again at midmorning and sank three heavy Japanese carriers—the Akagi, Kaga, and Soryu—and one heavy cruiser. In the late afternoon U.S. planes sank the fourth heavy carrier, the Hiryu, but Japanese aircraft severely damaged the U.S. carrier Yorktown. On June 6, a Japanese submarine torpedoed the crippled Yorktown and an escorting American destroyer. The Japanese, however, reeling from the loss of their carriers, began to withdraw on the night of June 4–5 without attempting a landing on Midway. Nevertheless, the Japanese did win a victory farther north: another carrier force had caused heavy damage at Dutch Harbor, in the Aleutians, during June 3–4, and Japanese invasion forces occupied Attu and Kiska without opposition on June 7.

If any one action can be called the turning point of the war in the Pacific, it is probably the Battle of Midway. There the Japanese lost their first-line carrier strength and most of their best-trained naval pilots. There was now some semblance of naval parity in the Pacific. For the Allies, also, it was a great strategic victory: the Japanese were prompted to cancel their plans to invade New Caledonia, Fiji, and Samoa and lost all but the last vestiges of their earlier strategic initiative.