In the autumn of 1943, following spectacular victories earlier in the war, Japan was on the defensive. It had suffered heavy aircraft and ship losses in the South Pacific, where the Allies were advancing up the Solomon Islands chain and along the coast of New Guinea. And now another Allied offensive was brewing in the Central Pacific. What the Japanese needed was time to rebuild their forces and prepare a comeback.
Recognizing that it could not defend everywhere, Japan established a National Defense Zone. Territories within that area, considered essential and to be held at all costs, included the Combined Fleet base at Truk Atoll, known as the “Gibraltar of the Pacific.” Outside the zone were eastern New Guinea, the northern Solomons, and the Bismarck Archipelago, including the Japanese bastion of Rabaul. The Japanese might relinquish these areas, but only after prolonged resistance to buy time. Rebuilding their forces and defenses was to be completed by the spring of 1944, followed by renewal of the offensive during the summer.