The Bougainville counterattack, also known as the Second Battle of Torokina, was an unsuccessful Japanese offensive against the Allied base at Cape Torokina on Bougainville Island in the Pacific Theater of World War II. The Japanese attack began on 8 March 1944 after months of preparation and was repulsed by United States Army forces in fighting which lasted until 25 March. The attack was hampered by inaccurate intelligence and poor planning and was pushed back by the well-prepared Allied defenders, who greatly outnumbered the Japanese force. The Japanese suffered severe casualties, while Allied losses were light.
The goal of the offensive was to destroy the Allied beachhead, which accommodated three strategically important airfields. The Japanese mistakenly believed that their forces were about as large as the units deployed to defend the Allied positions. The Allies detected Japanese preparations for the attack shortly after they began in early 1944 and strengthened the base's defenses. None of the three Japanese forces which conducted the attack was able to penetrate far into the Allied perimeter, although there was intense fighting for several positions.
The Bougainville counterattack was the last major Japanese offensive in the Solomon Islands campaign. Following the engagement the Japanese force withdrew from the Empress Augusta Bay area, and only limited fighting took place until late 1944, when Australian troops took over from the Americans and began a series of advances across the island until the end of the war in August 1945.
Background
Bougainville Island lies at the northwestern end of the Solomon Islands archipelago. The island is 125 mi (201 km) long and 38 mi (61 km) wide at its broadest point. The island is roughly shaped like a fiddle. The interior of Bougainville is dominated by two ranges of mountains that are covered with montane rainforests. The coastal plains are swampy and largely covered with mangroves and lowland rainforests. Bougainville has a tropical climate with heavy rain being common at all times of the year, producing the Solomon Islands rain forests ecoregion. There were two active volcanoes. At the time of World War II, most of Bougainville's population of about 50,000 lived in small settlements in the north of the island and along its northeastern coast. The area in and around the American perimeter in March 1944 was lightly populated. There were no formed roads, although a track ran along the coast and another crossed the interior.
At the outbreak of the Pacific War, Bougainville formed part of the Australian-administrated Mandated Territory of New Guinea. The small number of Australian public servants and plantation managers on Bougainville fled the island in January 1942, and it came under Japanese control that March. Few Japanese troops arrived until 1943, when the island's garrison was expanded to a peak strength of 65,000. After their arrival, the Japanese conscripted some of the locals to work as laborers. Conditions were harsh and often they were not paid. As the Allied bombing campaign in the Pacific intensified throughout 1943, the conditions imposed on the locals grew more harsh as food supplies dwindled and instances of disease grew.
The Bougainville campaign began on 1 November 1943 when the United States I Marine Amphibious Corps landed at Cape Torokina, around Empress Augusta Bay on the west coast of the Japanese-held island. The Allied invasion aimed to establish a defensive perimeter around Cape Torokina within which airfields would be built to attack the major Japanese base at Rabaul and support other operations in the region. The Allies did not intend to conquer the entire island, and the invasion area was mainly selected on the grounds that it was lightly defended and distant from the main Japanese bases at the northern and southern ends of Bougainville.
In addition to the advantages to be gained from distance from the Japanese bases, the American planners judged that a beachhead in the Cape Torokina area would be defensible. The U.S. Marine Corps official history of the fighting on the island states that "the Cape Torokina plain, bordered by the natural obstacles of the Laruma River to the northwest, the mountains inland, and the Torokina River to the southeast, fell into an ideal defensive area about 6 mi (9.7 km) deep and 8 mi (13 km) long which could be defended by the Allied forces then available". The planners judged that any force large enough to pose a threat to the beachhead would need at least three months to reach the area by travelling overland from the Japanese bases. While a Japanese counter-landing could potentially deposit a large force in the Cape Torokina area, the United States Navy was confident that it could stop any such operation.
The Japanese commander on Bougainville, Lieutenant General Harukichi Hyakutake, initially believed that the landing at Empress Augusta Bay was a diversion and would be followed by a direct assault on the south of the island. However, he conducted several small and unsuccessful attacks against the beachhead in early November after being ordered to do so by the Eighth Area Army, his superior headquarters. These involved units from Hyakutake's 17th Army and forces dispatched directly from Rabaul. After these attacks were defeated, a local counterattack with four battalions was planned for 22 November, but this plan was scrapped by the Eighth Area Army. The United States forces subsequently expanded their beachhead and defeated the Japanese in the area in a series of battles in November and December. Most of the Japanese units involved in these engagements were destroyed, but the casualties inflicted on the 17th Army were not crippling; the Americans captured 25 prisoners and a small amount of equipment and estimated that over 2,458 Japanese had been killed.
After pushing the Japanese back, the American forces began work on building defense lines to protect the airfield complex in late November. These defenses were completed by 15 December and comprised trenches, foxholes and fortified emplacements for machine guns and artillery. Barbed wire was strung along the 22,500 yd (20,600 m) horseshoe-shaped perimeter, and fields of fire were cleared 100 yd (91 m) ahead of all positions. All trails leading to the area were blocked with obstacles, and land mines were placed on other routes which might be used by the Japanese. Artillery and mortars were emplaced in positions where they could support any part of the defensive perimeter, and fire plans were developed to allow for rapid bombardments of all possible approach routes. Several searchlights were also deployed to illuminate the front lines. An outpost was established around Ibu, to the north of the perimeter, for early warning. The U.S. Army's official history of operations on Bougainville describes the American defenses as "formidable".
The construction of several airfields within the perimeter at Empress Augusta Bay began shortly after the landing. This work was conducted by eight United States Navy Seabee battalions and a brigade of engineers from New Zealand. An airfield capable of supporting fighters opened at Cape Torokina on 9 December, and a squadron of U.S. Marine Corps fighters began operating from it the next day. Two airfields capable of accommodating large numbers of light and medium bombers were subsequently completed: Piva Uncle on 30 December and Piva Yoke on 9 January 1944. These were the closest Allied airfields to Rabaul and were used to greatly intensify the air campaign against the Japanese positions there. The Japanese air units stationed at Rabaul were worn down by frequent Allied aerial raids during early 1944, and the Japanese high command decided to withdraw them following a major attack on the key base at Truk in mid-February. This gave the Allies complete air superiority over the region.
Prelude
Preparations
In late December 1943 Hyakutake and the other senior Japanese officers on Bougainville concluded that the Allies did not intend to advance from their perimeter at Empress Augusta Bay or land elsewhere on the island, and they began planning a counterattack. Their plans were based around a mistaken assessment that there were 30,000 Allied personnel on the island, of whom 20,000 were combat troops with the remainder aircraft ground crews; the American combat strength was actually over 60,000. As a result of its experiences in the Guadalcanal campaign during 1942 and 1943, the 17th Army decided to conduct a single major attack against the perimeter rather than a series of offensives. During a visit to Bougainville on 21 January 1944, General Hitoshi Imamura, the commander of the Eighth Area Army, directed that the offensive should be launched in early March. Japanese historian Hiroyuki Shindo states that this date was chosen solely based on ration availability; the Japanese supply line from Rabaul had been cut when the Allies had captured the Green Islands in mid-February, and Japanese commanders wanted to attack before supplies were exhausted.
Preparations for the counterattack were made during the first months of 1944. As the bulk of the 17th Army was stationed in northern and southern Bougainville, engineers needed to develop roads and bridges to allow the troops to move to the hills inland from the American perimeter. The combat troops chosen for the attack spent 40 days throughout January and into February conducting unit level training, perfecting jungle assault techniques. All of the units selected for the offensive departed their bases by mid-February and advanced along the eastern and western coasts. Barges moved artillery, other equipment and 1,400 soldiers to a point east of Cape Torokina, around the Jaba–Mosigeta area; the guns and supplies were then carried overland into the hills. Only two weeks worth of rations were assembled, although Japanese planners believed these provisions would be sufficient to sustain 12,000 men for about one month.
The Allied force on Bougainville detected the Japanese buildup. Information on the movement of the 17th Army was gained from many sources, including signals intelligence, patrols conducted by U.S. Army troops into the interior of the island, aerial and naval patrols, and the interrogation of Japanese prisoners. Japanese troops were also detected around the outpost at Ibu, which was held by the 1st Fiji Battalion. In response, Allied aircraft attacked bridges and areas in which Japanese troops were believed to be located. PT boats and Landing Craft Infantry gunboats supported by PBY Catalina aircraft patrolled the coast of Bougainville and attacked Japanese barges but were unable to stop the movement of supplies and equipment by sea. American warships and aircraft also periodically bombarded the main Japanese bases on Bougainville.
Several small clashes were fought between Allied and Japanese forces during February. The Fijian force at Ibu was reinforced to a strength of about 400 personnel on 3 February but was withdrawn to the perimeter in the middle of the month after a larger body of Japanese troops surrounded the outpost and began to attack the U.S. Army units which were protecting its supply lines. All of the Fijian troops, along with 200 Bougainvillean civilians who had chosen to evacuate with them, reached the coast on 19 February. Other American patrols and positions to the north and northeast of the perimeter were also attacked, and the Allies concluded that the Japanese force was being concentrated in this area. Papers taken from the bodies of Japanese soldiers killed in this fighting also allowed the Allies to build up an accurate appreciation of the Japanese plan of attack as well as the order of battle of the forces involved. Intelligence information detailing the Japanese plans was then distributed to American soldiers holding the perimeter through various means, including notices posted on unit bulletin boards.