Question: What division of the American armed forces fought the Imperial Japanese Army, also know as the "Dai-Nippon Teikoku Rikugun", or "Army of the Greater Japanese Empire", at Bougainville during World War Two?
Context: The Imperial Japanese Army (IJA; 大日本帝國陸軍 "Dai-Nippon Teikoku Rikugun"; "Army of the Greater Japanese Empire") was the official ground-based armed force of the Empire of Japan from 1868 to 1945.  It was controlled by the Imperial Japanese Army General Staff Office and the Ministry of War, both of which were nominally subordinate to the Emperor of Japan as supreme commander of the army and the navy.  Later an Inspectorate General of Aviation became the third agency with oversight of the army.  During wartime or national emergencies, the nominal command functions of the emperor would be centralized in an Imperial General Headquarters (IGHQ), an ad-hoc body consisting of the chief and vice chief of the Army General Staff, the Minister of War, the chief and vice chief of the Naval General Staff, the Inspector General of Aviation, and the Inspector General of Military Training. The Imperial Japanese Navy fielded naval paratroopers during World War II.  The troops were officially part of the Special Naval Landing Forces (SNLF or "Rikusentai").  They came from the 1st, 2nd and 3rd Yokosuka SNLFs.  The 2nd Yokosuka took no part in any airborne operations and became an island defensive base unit.  They were under the operational control of the Imperial Japanese Navy Air Service (IJNAS or "Dai-Nippon Teikoku Kaigun Koku Hombu").  "Rikusentai" paratroopers should not be confused with the Imperial Japanese Army paratroopers, known as "Teishin". The Imperial Japanese Navy (IJN; Kyūjitai: 大日本帝國海軍 Shinjitai: 大日本帝国海軍 "   " or 日本海軍 "Nippon Kaigun", "Navy of the Greater Japanese Empire") was the navy of the Empire of Japan from 1868 until 1945, when it was dissolved following Japan's defeat and surrender in World War II.  It was controlled by the Imperial Japanese Navy General Staff and the Ministry of the Navy, both of which were nominally subordinate to the Emperor of Japan as supreme commander of the army and the navy.  The Japan Maritime Self-Defense Force (JMSDF) was formed after the dissolution of the IJN. The Koishikawa Arsenal (小石川工廠 , Koishikawa Kōshō ) , formally Imperial Japanese Army Tokyo Arsenal (日本帝国陸軍東京砲兵工廠 , Nippon Teikoku Rikugun Tokyo Hōheikōshō ) was an arsenal in the Koishikawa area of Tokyo, on the grounds of today's Tokyo Dome City and the Koishikawa Kōrakuen Garden.  It was located on the ground of the former residence of the Prince of Mito. The Koiari Raid was a battle that occurred between 28–29 November 1943 in the Pacific theater of World War II between American and Japanese forces.  Part of the Bougainville campaign, the raid involved a landing by a battalion-sized force of United States Marines to harass Imperial Japanese Army troops on Bougainville Island.  The raid was a failure for the Americans as they were attacked by a larger-than-expected Japanese force and as a result the Marines were withdrawn from the beachhead without having achieved any of their objectives. The Imperial Japanese Navy Air Service (大日本帝國海軍航空隊 , Dai-Nippon Teikoku Kaigun Kōkū-tai ) was the air arm of the Imperial Japanese Navy during World War II.  The organization was responsible for the operation of naval aircraft and the conduct of aerial warfare in the Pacific War. The Battle of Piva Forks, also known as the Battle of Numa–Numa Trail, was an engagement that took place during the Bougainville campaign in World War II.  Occurring between 18 and 25 November 1943 on Bougainville Island in the South Pacific, the battle involved troops from the United States Marine Corps and the United States Army fighting against Imperial Japanese Army forces and took place amidst the context of the expansion of a beachhead that US forces had established around Torokina on the western side of the island. The Battle of Hellzapoppin Ridge and Hill 600A was a series of engagements fought in mid-December 1943 on Bougainville between forces of the United States Marine Corps and the Imperial Japanese Army.  Although minor in terms of casualties and in comparison to other battles in the campaign, the battle was the last significant action undertaken by the 3rd Marine Division on the island before they were replaced by United States Army soldiers from XIV Corps.  It resulted in the capture of the two positions by the Marines with the support of artillery and aircraft, and the withdrawal of the Japanese forces as the American perimeter, which had been established around Torokina, was expanded towards the Torokina River. The Imperial Japanese Army Air Service (often called the Imperial Japanese Army Air Force (大日本帝國陸軍航空部隊 , Dainippon Teikoku Rikugun Kōkūbutai ) (IJAAS or IJAAF), was the land-based aviation force of the Imperial Japanese Army.  As with the IJA itself, the IJAAS was developed along the lines of Imperial German Army Aviation so its primary mission was to provide tactical close air support for ground troops while maintaining a limited air interdiction capability.  The IJAAS also provided important reconnaissance support for the Army.  However, the Army Air Service usually did not control the light aircraft or balloons deployed and operated by the IJA artillery battalions as spotters or observers.  Although the Army Air Service engaged in strategic bombing of enemy cities such as Shanghai, Nanking, Canton, Chongqing, Rangoon, and Mandalay, this was not its primary mission, and it lacked the heavy strategic bombers as were later deployed by the United States Army Air Forces. Dai-gensui (grand marshal; literally "great marshal" (大元帥 ) ) was the highest rank of the Greater Imperial Japanese Army and the Imperial Japanese Navy from the 1870s to 1945, when the Empire of Japan was dissolved.  The rank was only ever held by the Emperor of Japan as commander-in-chief of the Empire's Armed Forces and, separately, the highest ranking officer in each of the Armed Services.  The rank was equivalent to a "generalissimo" or general of the armies and admiral of the navy, being a six-star rank senior to the rank of "gensui" ("marshal").  It formally became obsolete in 1947 when the Imperial Japanese armed forces were abolished.
Answer: Marine Corps