Located on Simpson Harbor at the northeastern tip of New Britain, Rabaul served as an air and naval base and troop staging area for Japanese conquests in New Guinea and the Solomon Islands. As the advancing Japanese approached New Britain, Australian authorities, who administered the former German colony under terms of a mandate from the League of Nations, evacuated the Australian women and children living there. These dependents had already departed when the enemy landed on 23 January 1942, capturing Rabaul by routing the defenders, some of whom escaped into the jungle to become coastwatchers providing intelligence for the Allies. The Australian coastwatchers, many of them former planters or prewar administrators, reported by radio on Japanese strength and movements before the invasion and afterward attached themselves to the Marines, sometimes recruiting guides and bearers from among the native populace.

Once the enemy had seized Rabaul, he set to work converting it into a major installation, improving harbor facilities, building airfields and barracks, and bringing in hundreds of thousands of soldiers, sailors, and airmen, who either passed through the base en route to operations elsewhere or stayed there to defend it. Rabaul thus became the dominant objective of General Douglas MacArthur, who escaped from the Philippines in March 1942 and assumed command of the Southwest Pacific Area. MacArthur proposed a two-pronged advance on the fortress, bombing it from the air while amphibious forces closed in by way of eastern New Guinea and the Solomon Islands.

Even as the Allies began closing the pincers on Rabaul, the basic strategy changed. Despite MacArthur's opposition, the American Joint Chiefs of Staff decided to bypass the stronghold, a strategy confirmed by the Anglo-American Combined Chiefs of Staff during the Quadrant Conference at Quebec in August 1943. As a result, Rabaul itself would remain in Japanese hands for the remainder of the war, though the Allies controlled the rest of New Britain.