Leading Up to Battle
During the first few months after World War II expanded into the Pacific in late 1941, Japan scored victory after victory, taking control of islands ranging from the Aleutians (off the coast of Alaska) to the Philippines. In January 1942, Japanese troops overpowered an Australian garrison at Rabaul, on the southwestern Pacific island of New Britain (now part of Papua New Guinea). By the summer of 1943, Rabaul served as a major Japanese base, with more than 100,000 troops garrisoned there.
The aggressive Allied counteroffensive strategy adopted in mid-1943 called for amphibious assaults on selected Japanese-held islands as part of a drive towards the Philippines and the Japanese home islands. This “island-hopping” or “leapfrogging” strategy banked on the belief that isolating Japanese forces (such as those on Rabaul) would be just as effective as destroying them through direct attacks, and far less costly to Allied forces. Encircling Rabaul, in particular, would nullify the Japanese threat from the Solomon Islands and the Bismarck Archipelago (which included New Britain), while a second prong of the Allied advance drove through the central Pacific via the Gilbert and Marshall Islands.
At the end of April 1943, the Allies developed their plan for encircling Rabaul, codenamed “Operation Cartwheel.” It called for MacArthur to approach Rabaul from the southwest, through New Guinea and the southern Bismarcks, while Halsey would advance through the Solomons, forming two pincers that would close in on the Japanese base. Meanwhile, the Japanese were busy reinforcing and reorganizing their forces in the South Pacific in anticipation of an Allied offensive. General Hitoshi Imamura, headquartered at Rabaul, commanded Japan’s 17th Army in the Solomons; they were reinforced by the 18th Army, tasked with defending northern New Guinea.
In late June, the two-pronged Allied drive toward Rabaul began, both in New Guinea and the Solomons. Lae, on the northern New Guinea coast, fell in mid-September; U.S. forces then seized Saidor, opposite Cape Gloucester, on the westernmost tip of New Britain. By October 1943, Halsey’s forces were ready to attack Bougainville, the largest and westernmost island in the Solomon chain, located just 200 miles from Rabaul at the narrowest sea crossing. Reinforcements (some 37,500 men) from the Japanese 17th Army were sent to Bougainville, concentrated at Buin, near the island’s southern end, and on small islets off the shore of the main island. This left Empress Augusta Bay, to the north, open to a landing by U.S. Marines on November 1, 1943, four days after New Zealand forces captured the tiny Treasury Islands, south of Bougainville. In the ensuing battle, American ships engaged thinly dispersed Japanese defenders, sinking Japanese cruisers and a destroyer while the 5th Army Air Force bombed Japanese airstrips and supported the Marine landing.
Closing in on Rabaul
In conjunction with MacArthur’s advance in New Guinea, Halsey’s forces were closing in on the Japanese at Rabaul. By November 21, U.S. troops from the 3rd Marine and 37th Army Divisions had firmly established themselves on Bougainville. In addition, Halsey ordered an attack against the powerful Japanese fleet just as it set forth from Rabaul–a risky gamble, as it put a two-carrier American task force in range of Japan’s huge air power. Through skillful deployment of land-based aircraft, the Allied force kept Japan’s planes at bay, leaving the U.S. carriers unscathed and allowing them to launch waves of torpedo- and dive-bombers against the fleet, which was forced to withdraw to distant Truk Island. Meanwhile, the Marines at Bougainville launched a series of intensive air raids against Rabaul.
On December 15, Allied troops landed at Arawe, on the southwestern coast of New Britain, diverting Japanese focus from Cape Gloucester, on the northwestern coast, in time for a major Allied landing there on December 26. After repulsing a Japanese counterattack, the Allies captured Cape Gloucester and its major airstrip by January 16, 1944, and set up a solid defensive line. New Zealand took the Green Islands, southeast of New Guinea, in mid-February, while U.S. forces invaded the Admiralty Islands later that month and captured the Emirau Islands by March 20. On each island they captured, the Allies constructed air bases, allowing them to block any westward movement by the Japanese. In this way, the Allies tightened their stranglehold on Rabaul, effectively neutralizing the 100,000 Japanese troops stationed there by the end of March 1944.