The Elkton III Plan was the Allied plan for the reduction of the major Japanese base at Rabaul on New Ireland. It involved a two-pronged advance, with General MacArthur's forces operating on New Guinea and Admiral Halsey's in the Solomon Islands, and would be implemented as Operation Cartwheel.
The basic idea of a two-pronged advance towards Rabaul had been developed during 1942. Early in 1943 MacArthur's HQ produced their first concrete plan for the advance, the Elkton plan. Elkton I was produced on 12 February 1943, and Elkton II on 28 February. This was presented to the Joint Chiefs of Staff on 12 March 1943. Elkton II was a five step plan. Step 1 was the capture of airfields on the Huon Peninsula of New Guinea. Step 2 was a similar operation on New Georgia. Step 3 would see the Allies capture bases on New Britain and Bougainville. Step 4 was the capture of Kavieng, on New Ireland. Step 5 was the capture of Rabaul.
It quickly became clear that there would not be enough troops available to carry out this ambitious plan during 1943. MacArthur and Halsey's representatives were asked to work out how far they could get with the troops at their disposal, and decided that they could reach Madang in New Guinea, secure the south-eastern part of Bougainville and the western part of New Britain. The Joint Chiefs approved this plan on 28 March in a directive that laid out the outline of what would become Operation Cartwheel. MacArthur was given overall command of the joint operations, with Admiral Halsey operating under him.
MacArthur and Halsey were given the task of produced a more detailed outline for Elkton III. Their first face-to-face meeting, at Brisbane, was a great success. Halsey was very impressed with MacArthur, and the two men quickly developed a very effective working relationship. The official Elkton III plan was issued on 26 April 1943, after this successful meeting. The official aim was to push the Allied bomber line towards Rabaul to bring the Japanese base into the range of increasing numbers of Allied aircraft,
All of the attacks that were to be carried out as part of the Elkton III plan were given the overall codename Operation Cartwheel, with each major attack within the plan getting its own codename. Cartwheel would eventually cover five major operations, and many more minor attacks and landings.
D-Day for Operation Cartwheel was eventually set at 30 June 1943, so month one of the planned timetable was July 1943
Month 1 - July 1943
Month 2 - August 1943
Month 3 - September 1943
Month 4 - October 1943
Month 5 - November 1943
Month 6 - December 1943
Month 7 - January 1944
Month 8 - February 1944
Once Cartwheel started a great deal of debate went into the future direction of the war, and also the fate of Rabaul. As early as July the Joint Chiefs of Staff were considering bypassing Rabaul altogether, and this policy was approved by President Roosevelt in August. The official plans reached MacArthur's HQ on 17 September.
Cartwheel was to start with minor operations by both forces. South West Pacific was to carry out Operation I, the occupation of Woodlark Island and Kiriwina in the Trobriand Islands. These were both undefended, and could be used to provide air bases for the later stages of the campaign. Operation I was to take place in month one, June-July 1943 in the original timetable.
At the same time South Pacific was to carry out Operation A, a series of minor ground attacks in the Solomon Islands, designed to take advantage of any Japanese weakness, and to pin down any Japanese aircraft in the islands.
The second stage of the plan would begin with Operation II, the occupation of Lae, Salamaua, Finschhafen and Madang on the north-eastern coast of New Guinea. This would start with the attack on Lae (Operation IIa), to start two months after Cartwheel (September to mid-October 1943). Next would come the attacks on Salamaua and Finschhafen (Operation IIb), six weeks after the start of IIa (mid October to November 1943). Finally Madang would be attacks (Operation IIc). The overland approach to Madang would be given one month (mid November to mid December 1943) and the attack itself would start in mid December 1943.
While Operation II got underway South Pacific would offer general support for South West Pacific. South Pacific would then go back onto the offensive five and a half months into Cartwheel with Operation B, the conquest of New Georgia and the seizure of Faisi in the Shortland Islands and Buin on the south-eastern corner of Bougainville. About six weeks were allocated to Operation B, but the timetable appears to have been developed without much input from Halsey's command, and wasn't really followed.
Phase three would see both commands carry out almost similtanous operations. South West Pacific would start first, with Operation III, the invasion of western New Britain. Operation IIIa would be an attack on Cape Gloucester and Arawe and mid December 1943, followed by Operation IIIb, an attack on Gasmata and Talasea in mid-January 1943.
South Pacific would begin Operation C two weeks after Operation III, in January 1944 on the original timetable. Operation C would complete the neutralisation of Bougainville, with attacks on Kieta on the east coast and Buka, an island off the northern tip.
Once all of these operations had been carried out both Rabaul and Kavieng would be within range of Allied light bombers and fighters, allowing the air forces to eliminate any threat from these bases.
The Elkton III plan was implemented as Operation Cartwheel, which began on 30 June 1943. Although the exact timetable wasn't always followed, Carthwheel achieved its main aims by the spring of 1944, only a couple of months behind schedule. Rabaul and Kavieng would be left to wither on the vine, and remained in Japanese hands to the end of the war, but from 1944 neither of them posed any real threat to Allied operations.