The Bougainville campaign was a series of land and naval battles of the Pacific campaign of World War II between Allied forces and the Empire of Japan, named after the island of Bougainville, one of the Solomon Islands. It was part of Operation Cartwheel, the Allied grand strategy in the South Pacific.
The campaign took place in the Northern Solomons in two phases. The first phase, in which American troops landed and held the perimeter around the beachhead at Torokina, lasted from November 1943 through November 1944. The second phase, in which primarily Australian troops went on the offensive, mopping up pockets of starving, isolated but still-determined Japanese, lasted from November 1944 until August 1945, when the last Japanese soldiers on the island surrendered. Operations during the final phase of the campaign saw the Australian forces advance north towards the Bonis Peninsula and south towards the main Japanese stronghold around Buin, although the war ended before these two enclaves were completely destroyed.
Japanese occupation
Before the war, Bougainville had been administered as part of the Australian Territory of New Guinea, even though geographically Bougainville is part of the Solomon Islands chain. As a result, within the various accounts of the campaign it is referred to as part of both the New Guinea and the Solomon Islands campaigns.Tanaka 1980; Lofgren 1993; James 2016.
During their occupation the Japanese constructed naval aircraft bases in the north, east, and south of the island; but none in the west. They developed a naval anchorage at Tonolei Harbor near Buin, their largest base, on the southern coastal plain of Bougainville. On the nearby Treasury and Shortland Islands they built airfields, naval bases and anchorages.Miller 1959, p. 234. These bases helped protect Rabaul, the major Japanese garrison and naval base in Papua New Guinea, while allowing continued expansion to the southeast, down the Solomon Islands chain, to Guadalcanal and beyond. To the Allies, Bougainville would later also be considered vital for neutralizing the Japanese base around Rabaul.Rentz 1946, p. 1.
In March–April 1942, the Japanese landed on Bougainville as part of their advance into the South Pacific. At the time, there was only a small Australian garrison on the island which consisted of about 20 soldiers from the 1st Independent Company and some coastwatchers. Shortly after the Japanese arrived, the bulk of the Australian force was evacuated by the Allies, although some of the coastwatchers remained behind to provide intelligence. Once secured, the Japanese began constructing airfields across the island.Keogh 1965, p. 414. The main airfields were on Buka Island; the Bonis Peninsula in the north; Kahili and Kara in the south; and Kieta on the east coast; while a naval anchorage was constructed at Tonolei Harbor near Buin on the southern coastal plain, along with anchorages on the Shortland Islands group.Murray 2001, p. 169–195, Spector 1985, pp. 152–153
The airfield at Kahili was known by the Japanese as Buin Airfield, and to its south was an airfield on Ballale Island in the Shortland Islands. These bases allowed the Japanese to conduct operations in the southern Solomon Islands and to attack the Allied lines of communication between the United States, Australia and the Southwest Pacific Area.
At the opening of the Allied offensives, their estimates of Japanese strength on Bougainville varied widely, ranging between 45,000 and 65,000 army, navy, and labour personnel. These forces constituted the Japanese 17th Army, commanded by General Harukichi Hyakutake.James 2016, p. 234. Hyukatake reported to General Hitoshi Imamura, commander of the Japanese Eighth Area Army, headquartered at Rabaul on New Britain. Naval command at Rabaul was the responsibility of Vice Admiral Jinichi Kusaka, commander Southeast Area Fleet. The level of cooperation between these two officers was greater than that usually found between the branches of the Japanese armed forces.Morison 1958, p. 394
The 17th Infantry Group occupied Bougainville and consisted of the 81st Infantry Regiment and the III Battalion, 53rd Infantry Regiment under Major General Kesao Kijima. Elements of the 6th Division had responsibility for the island south of Tarina.Tanaka 1980, p. 72.
Allied planning
Choice of Bougainville Reduction of the main Japanese base at Rabaul was the ultimate goal of the Allied offensive in the Solomons. To achieve this, Allied planners formulated Operation Cartwheel. By 1943 Rabaul was within range of Allied heavy bombers, but a closer airfield was needed for light bombers and escort fighters. Thus, the entire island of Bougainville did not need to be occupied; only enough relatively flat land to support an airbase was required. According to historian Samuel Eliot Morison, this "was the one and only reason why the JCS authorized Halsey to seize a section of Bougainville: to establish forward airfields for strikes on Rabaul."Morison 1958, p. 281
The area around Cape Torokina was determined to be an acceptable location. The Japanese were not there in force and had no airfield there. Empress Augusta Bay had a somewhat protected anchorage, and the physical barriers to the east of the cape – for instance the mountain ranges and thick jungle – meant that mounting a counterattack would be beyond the capabilities of the Japanese for weeks, if not months, which would allow the US forces to consolidate after landing and give them enough time to establish a strong perimeter.Morison 1958, pp. 283–284 The preparation for landings at Cape Torokina became known as Operation Cherry Blossom.
Preparations for the landings
Bougainville lay within the Southwest Pacific Area, so operations were nominally under the command of General Douglas MacArthur, whose headquarters were in Brisbane, Australia. Although MacArthur had to approve all major moves, he gave planning and operational control to Admiral William F. Halsey, Commander U.S. Third Fleet, headquartered at Nouméa on New Caledonia.Morison 1958, p. 282 In mid-October, Halsey set 1 November 1943 as the date for the invasion of Bougainville.Morison 1958, p. 284
By early October, it was clear to the Japanese that the Allies were planning a follow-up offensive to the Allied capture of the New Georgias, although the target was uncertain. The commander of the Japanese Combined Fleet, Admiral Mineichi Koga, flying his flag aboard the battleship from Truk Lagoon, sent all of his carrier aircraft to Rabaul. These planes would combine with the land-based air force already there and bomb Allied bases and supply routes as part of a plan the Japanese called Operation RO. In the event, this plan achieved very little besides further attrition to the Japanese air arm as the Japanese aircraft suffered heavy losses,Miller 1959, pp. 233–248. which later prevented the Japanese aircraft from intervening against the US landings in the Gilbert and Marshall Islands.Shindo 2016, p. 61.
To confuse the Japanese as to the Allies' real target, two other invasions were carried out. The Treasury Islands, just southwest of the Shortlands, were occupied 27 October by the 8th Brigade Group, 3rd New Zealand Division under the command of Brigadier Robert Row, and a temporary landing was effected on Choiseul, one of the major islands in the Solomons chain.Morison 1958, pp. 293–296 Unlike on Guadalcanal and the New Georgias, Allied planners were unable to gain valuable intelligence from coastwatchers or small Australian Army detachments as the Japanese had driven them off the island long before plans for Operation Cherry Blossom began.Morison 1958, pp. 280–281
Forces allocated
Rear Admiral Theodore Wilkinson, Commander Third Fleet Amphibious Forces, was assigned by Halsey to direct the landings at Cape Torokina from aboard his flagship, the attack transport .Miller 1959, p. 244. The ships under Wilkinson's command would disembark the I Marine Amphibious Corps, commanded by Major General Alexander Vandegrift, victor of the land campaign on Guadalcanal. Vandegrift's force, a total of 14,321 men, consisted of the 3rd Marine Division (reinforced), under Major General Allen H. Turnage, the U.S. Army's 37th Infantry Division, under Major General Robert S. Beightler, and the Advance Naval Base Unit No. 7.Morison 1958, p. 289
Landings at Cape Torokina
First day: 1–2 November 1943
Three groups of transports converged in Empress Augusta Bay on the morning of 1 November. The existing maps of the Bougainville coast that the Allies possessed were highly unreliable German Admiralty charts from about 1890. A few corrections had been made by reconnaissance flights and submarine scouting, but some longitudes were still wrong. Indeed, Morison recounts that "near the end of the approach, when the navigating officer of a transport was asked by the captain for his ship's position, he replied, 'About three miles inland, sir!'"Morison 1958, pp. 298–299 Morison further recounts the scene of the landing in the following passage:
From the difficult landings at Guadalcanal and the New Georgias, Admiral Wilkinson had learned a significant lesson about the necessity of rapid unloading and getting his slow, vulnerable transports away from the landing area. To this end, he loaded his transports only half full and his cargo ships one-quarter full, and made sure that 30% of the troops on the beach assisted in unloading.Morison 1958, p. 303 The Japanese, having been taken by surprise, were unable to mount an air assault on the invasion fleet. Wilkinson, grateful that his transports were able to land almost the entire troop contingent and a large amount of materiel unmolested by air attack, ordered them out of the area around sundown.Morison 1958, p. 304
Japanese response
Japanese forces around the landing area were limited to no more than platoon strength, as they had not expected an attack in the area, and their logistics system was unable to support greater numbers. When word of the landings reached Rabaul, Vice Admiral Tomoshige Samejima, Commander of the Japanese Eighth Fleet, immediately embarked 1,000 troops from the II Battalion, 54th Infantry RegimentTanaka 1980, p. 73. onto five destroyer-transports at Rabaul and sent them to Cape Torokina. Escorting the transports was a force of two heavy cruisers, two light cruisers and six destroyers led by Vice Admiral Sentaro Omori. During the night voyage to Torokina, the Japanese ships were spotted by an American submarine and possibly by a search plane. Concerned that he had lost the element of surprise, Omori radioed Samejima to ask permission to send the slow-moving transports back to Rabaul but to continue with the combat ships to attack the American transports that he assumed were still in Empress Augusta Bay. Samejima concurred, and Omori pressed ahead with his cruisers and destroyers.Morison 1958, pp. 305–306
At the same time, Rear Admiral Stanton Merrill was steaming toward the Bay with four light cruisers and eight destroyers. The two forces met in the early morning hours of 2 November in the Battle of Empress Augusta Bay, in which the Japanese lost the light cruiser and the destroyer .Gailey 1991, p. 83.
Carrier raid on Rabaul