Bougainville was a 250-square-mile island with 37,500 entrenched Japanese. Experience with Guadalcanal and New Georgia led to a new plan. Bougainville was still the objective. From air fields there, American planes could neutralize Rabaul, less than 250 miles away on New Britain. From Bougainville, the Japanese could defend Rabaul. The island had to be taken, but not necessarily in its entirety, all at once.
American machine gun crew awaits the Japanese attack on Bougainville, March 1944.
Following the successful campaign to take Guadalcanal (7 August 1942 - 21 February 1943), United States forces began a slow northwest advance up the Solomons chain leading toward Rabaul on New Britain. Airbases on Guadalcanal were expanded, the Russells were taken for an advanced fighter base, and an amphibious campaign covered by planes from the Russells took Munda and other points on New Georgia in the Central Solomons. Landings by American and New Zealand troops at Mono and Stirling in the Treasury Islands, south of Bougainville, on 25-27 October 1943, and on Choiseul, a large island near Bougainville, also on the 27th, completed the preliminaries.
Rather than try to eliminate the Japanese from Bougainville, no doubt requiring a slow, difficult and bloody campaign, the plan was to take a limited area around the best port, at lightly defended Empress Augusta Bay, enough to build and defend a major airfield. From that field, American planes could bomb Rabaul as well as New Guinea, and range over the South Pacific all the way to the Philippines, assuring security from the air for the convoys and task forces that would invade the Philippines in October 1944.
The Invasion of Bougainville
Seebees constructing an airfield, placing Marston mats. Bougainville, December 1943.
As the invasion was prepared, Air Command, Solomons kept the five Japanese fields on Bougainville under such pressure that they were useless by invasion day. Harassing attacks from the Treasury Islands and Choiseul were directed everywhere except the intended invasion site, deceiving the defenders.
The 3d Marine Division landed on the west coast of Bougainville at Empress Augusta Bay on 1 November 1943, establishing a beachhead against mixed opposition and with excellent logistical organization. Between seven and eight thousand Marines went ashore in the first wave, landing on twelve predetermined beaches over four miles of coast. Steep beaches and surf caused nearly 90 landing craft to broach or swamp. Over the next two weeks more than 33,000 Marine and Army troops and 23,000 tons of supplies went ashore, but the Japanese also landed reinforcements resulting in numerous battles, decisive for the Americans. By 14 November, 3d Marine Division on the right (east) and the U.S. Army 37th Infantry Division on the left (west) reached their successive objectives. Continuing enemy ground resistance and airstrikes sometimes involved quite severe battles.
The American beachhead was on the plain between the coast and the Crown Prince Range, an imposing volcanic mountain range held by the Japanese. The Army fought on relatively firm ground, but he Marines had to contend with tropical swamps of the worst kind. The two American divisions eventually drove the Japanese out and occupied the plain and nearby foothills and high points overlooking the beachhead. After many significant firefights, by Christmas 1943 the Japanese were driven east of the Torokina River, and behind the Final Inland Defense Line. American units now occupied the high ground which controlled the perimeter and the beachhead at Empress Augusta Bay was secure. Although the Japanese held higher ground inland, it was too far from the American perimeter to confer any important advantage.
From the new airstrips built by the Seabees, Allied planes neutralized enemy airfields in the northern part of Bougainville, and the Allied command made use of its naval and air superiority to contain the Japanese garrison on Bougainville. They cut the Japanese supply line to Rabaul by occupying the Green Islands on 14 February 1944 and Emirau Island on 20 March 1944. The Marines were withdrawn and Army units within the beachhead perimeter formed XIV Corps of six regiments that numbered 62,000 men by March 1944.
Japanese Counterattack on Bougainville
The Japanese eventually realized the Americans were not going on an offensive across Bougainville nor was another landing coming. If they wanted to engage the U.S. forces and interfere with the increasing air operations, they would have to attack. XIV Corps was ready with prepared positions along their 23,000-yard perimeter, with tactically important pieces of high ground properly manned and equipped.
Unlike at New Georgia, now it was the Japanese who would be assaulting prepared defenses, confronting booby traps, illumination devices, and minefields, then concertina wire shielding rifle pits and pillboxes protecting rifle squads with more than the usual number of automatic rifles and probably extra machine guns. Fields of fire fifty or more yards deep had been cleared to prevent attackers from sneaking within hand-grenade range. Searchlights as well as oil drums—each containing a bangalore torpedo surrounded with scrap metal—provided additional obstacles for an attacker. American field artillery, augmented in early March, was combined with the "Bougainville Navy" -- fire support destroyers -- and plentiful air support. Perhaps most important, the line was manned by six veteran U.S. Army infantry regiments.
Attacks started near midnight during the night of 8-9 March, and over the next few days spread all along the American perimeter. The Japanese mounted serious threats in several areas and inflicted major losses on some units. At the same time, American firepower decimated many Japanese units and kept the attackers from gaining a footing in any important position. During the night of 9-10 March, a determined Japanese attack captured South Knob and American counterattacks, air strikes, and artillery could not displace them until 15 March. Another major Japanese assault on the night of 11 March, against an Army position along a 3,900 yard front, was defeated by a determined defense and counterattacks to push back any infiltration of the American lines.
The Japanese regrouped in the jungle, gathering their remaining forces for a last attempt to break the American line. By 23 March they were ready, but, as before, captured Japanese documents and decrypted communications warned of the attack and the troops were ready. Although the Japanese launched a fierce attack, using all their remaining artillery, the American artillery, tank-infantry counterattacks, and stubborn defense of all positions crushed the Japanese assault and by midafternoon it was over.
In the March assaults, the Japanese incurred 5,000 dead, while the veterans of XIV Corps, who had used their superior defenses and fought determinedly and shrewdly, had 263 killed. Thereafter, the Japanese were unable to mount further offensive operations on Bougainville.
For several months after major combat operations had ended, American troops patrolled and hunted the remnants of Japanese units through Bougainville's vast jungles, but for practical purposes the end had come with the destruction of the Japanese counterattack in March 1944.
Fighting continued on Bougainville as gradually the Japanese were ground down. During October-December 1944, the U.S. ground forces were replaced by the Australian II Corps. A series of actions into the Spring of 1945 forced the Japanese into the Bonis Peninsula in the north. Allied attempts to finish off the Japanese on Bougainville did not succeed prior to the surrender of the Japanese government. The surrender of Japanese forces on Bougainville took place on 21 August 1945.
Aftermath of the Bougainville Campaign
Success at Bougainville isolated all Japanese forces left in the Solomons. The Japanese sustained comparatively heavy air and naval losses during the campaign, which further crippled the Japanese Combined Fleet and had a vital effect on the balance of naval power in the Central Pacific. The Seabees, working at a feverish rate, carved three airfields out of the jungles of Bougainville. From those bases the long-range, strategic effects of Bougainville were felt by the Japanese as American aircraft ranged the Pacific as far as the Philippines and supported operations in New Guinea.
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