Operation Cartwheel (1943–1944) was a major military operation for the Allies in the Pacific theatre of World War II. Cartwheel was an operation aimed at neutralising the major Japanese base at Rabaul. The operation was directed by the Supreme Allied Commander in the South West Pacific Area (SWPA), General Douglas MacArthur, whose forces had advanced along the northeast coast of New Guinea and occupied nearby islands. Allied forces from the South Pacific Area, under Admiral William Halsey, advanced through the Solomon Islands toward Bougainville. The Allied forces involved were from Australia, the Netherlands, New Zealand, the US and various Pacific Islands.
Japanese forces had captured Rabaul, on New Britain, in the Territory of New Guinea, from Australian forces in February 1942 and turned it into their major forward base in the South Pacific, and the main obstacle in the two Allied theatres. MacArthur formulated a strategic outline, the Elkton Plan, to capture Rabaul from bases in Australia and New Guinea. Admiral Ernest J. King, the Chief of Naval Operations, proposed a plan with similar elements but under Navy command. Army Chief of Staff George C. Marshall, whose main goal was for the US to concentrate its efforts against Nazi Germany in Europe and not against the Japanese in the Pacific, proposed a compromise plan in which the task would be divided into three stages, the first under Navy command and the other two under MacArthur's direction and the control of the Army. This strategic plan, which was never formally adopted by the US Joint Chiefs of Staff but was ultimately implemented, called for the following:
The protracted battle for Guadalcanal, followed by the unopposed seizure of the Russell Islands (Operation Cleanslate) on 21 February 1943, resulted in Japanese attempts to reinforce the area by sea. MacArthur's air forces countered in the Battle of the Bismarck Sea from 2–5 March 1943. The disastrous losses suffered by the Japanese prompted Admiral Isoroku Yamamoto to initiate Operation I-Go, a series of air attacks against Allied airfields and shipping at both Guadalcanal and New Guinea, which ultimately resulted in his death, on 18 April 1943.
MacArthur had presented Elkton III, his revised plan for taking Rabaul before 1944, on 12 February 1943. It called for him to attack northeastern New Guinea and western New Britain and for Admiral William F. Halsey Jr., then in command of the South Pacific Area, to attack the central Solomons. The plan required seven more divisions than were already in the theatre, which raised objections from the British. The Joint Chiefs responded with a directive that approved the plan if forces already in the theatre or en route were used and the implementation was delayed by 60 days. Elkton III then became Operation Cartwheel.
Cartwheel identified 13 proposed subordinate operations and set a timetable for their launching. Of the 13, Rabaul, Kavieng, and Kolombangara were eventually eliminated as too costly and unnecessary, and only 11 were actually undertaken (the Green Islands, only 117 miles from Rabaul, were substituted for Kavieng):
The New Guinea Force, under General Thomas Blamey, was assigned responsibility for the eastward thrusts on mainland New Guinea. The US 6th Army, under General Walter Krueger, was to take Kiriwina, Woodlark, and Cape Gloucester. The land forces would be supported by Allied air units under Lieutenant General George Kenney and naval units under Vice Admiral Arthur S. Carpender.
In the midst of Operation Cartwheel, the Joint Chiefs met with President Franklin Roosevelt and British Prime Minister Winston Churchill at the Quadrant Conference in Quebec City in August 1943. There, the decision was made to bypass and isolate Rabaul, rather than attempting to capture the base, and to attack Kavieng instead. Soon afterward, the decision was made to bypass Kavieng as well. Although initially objected to by MacArthur, the bypassing of Rabaul, instead of its neutralisation, meant that his Elkton plan had been achieved, and after invading Saidor, he then moved into his Reno Plan, an advance across the north coast of New Guinea to Mindanao.
The campaign, which stretched into 1944, showed the effectiveness of a strategy of avoiding major concentrations of enemy forces and instead aiming to sever the Japanese lines of supply and communication.
The Japanese Navy decided to try to save Rabaul by sending hundreds of airplanes from aircraft carriers based at Truk in December 1943 to counter the U.S. and Australian bombers. The only thing that this operation accomplished was the destruction of 200-300 irreplaceable carrier planes and the loss of experienced naval aviators. This degradation of the Japanese aircraft carrier air fleet led to preparations by the U.S. Navy to start the Marianas campaign a few months later. Also, the Admiralty Islands campaign was conducted starting in late February after the Allies confirmed that Rabaul no longer had any airplanes.
By February 1944 Rabaul had no more fighters or bombers for the rest of the war due to the non-stop bombing by land-based Allied airplanes only a few hundred miles from Rabaul after most of Operation Cartwheel was completed. 120 airplanes were evacuated to Truk on 19 February in an attempt to replace the destroyed Navy carrier airplanes. Rabaul's valuable mechanics attempted to leave Rabaul by ship on 21 February, but their ship, the Kokai Maru, was sunk by Allied bombers. Rabaul became a de facto prisoner of war camp.