The raider headquarters and both Marine battalions embarked in transports on 28 August and sailed for Guadalcanal. The New Georgia campaign had been a costly one. Each raider battalion had suffered battle casualties of more than 25 percent. In addition, sickness had claimed an even greater number. The 1st Raiders now had just 245 effectives; the 4th Raiders only 154.
In the immediate aftermath of the fall of New Georgia, the Allies seized other islands in the vicinity, to include Arundel, Vella Lavella, and Kolombangara. Thereafter the South Pacific command turned its attention to the next major step in the encirclement of Rabaul. There were several options, but the final choice was a landing on Bougainville, the largest island in the Solomons group. A month later MacArthur’s command would assault Cape Gloucester on the western end of New Britain. Rabaul would then be within range of Allied land-based fighter aircraft coming from two directions. Air power thus could neutralize the Japanese bastion and allow it to be by-passed. The scheduled D-day for Bougainville was 1 November 1943.
[Illustration: _Cape Torokina on Bougainville is seen after the Allies built an airstrip. Threatening Puruata Island, assaulted by the 3d Raider Battalion on 1 November 1943, is in the foreground. Tiny Torokina Island lies in between Puruata and the Cape._
Department of Defense Photo (USMC) 68047 ]
Several factors dictated Halsey’s scheme of maneuver for the offensive. First, he had too few transports and Marines to make a direct assault on the heavily defended enemy airfields located on the northern and southern ends of the island. Another consideration was the range of land-based fighters from bases in the Central Solomons--they could only effectively cover a landing in the southern half of Bougainville. The planners settled on the Empress Augusta Bay-Cape Torokina region on the western side of the island. Defenses were negligible there, and Bougainville’s difficult terrain would prevent any rapid reaction from enemy ground forces located elsewhere on the island. Once ashore, the invasion force would seize a defensible perimeter, build an airfield, and eventually neutralize the remainder of the island from this enclave. A patrol landed by submarine in late September discovered that the areas back of the landing beaches were swampy. Aerial reconnaissance in October also discovered the construction of new defenses. Neither of these facts changed the plan, however.