By early 1944, Allied submarines, particularly American submarines, were doing to the Japanese what German U Boat captains could only dream of. No cargo ship flying the Rising Sun was safe anywhere in the Pacific. Moreover, American industry was pumping out new ships faster than crews could be trained to man them. There were enough aircraft carriers that fast carrier “strike groups” were raiding islands and shipping all throughout the Central and South Pacific. Inefficiencies in Japanese industry meant they simply could not keep up with the losses, much less innovate and upgrade their current ship types. Finally, their “Outer Defensive Ring” was under siege and penetrated in a few places: The “Japanese Pearl Harbor”, the Truk lagoon in the Caroline Islands, was a beacon for submarines. And most of its ships and port facilities were destroyed in Operation Hailstone, a concerted air and naval attack to destroy shipping there on 16 February. Heeding the lessons of Tarawa, Nimitz made short work of the Japanese garrisons in the Marshall Islands. The Japanese 28th Army was in process of being destroyed in Burma. Australian, Kiwi and American troops under MacArthur were steadily marching across New Guinea. Landings and land based airpower on New Britain, Bougainville and New Georgia had already isolated and neutralized Rabaul, unbeknownst to the soldiers and Marines fighting toward it from Cape Gloucester. And MacArthur wasn’t even attempting to hide preparations for landings along the north coast of New Guinea and in the Admiralty Islands to its northeast. The Japanese had to fall back; Bushido be damned.
As early as September, 1943, the Japanese Imperial Headquarters considered the withdrawal to a smaller perimeter in the Pacific but the admirals did not want to lose face in front of their bitter rivals, the generals of the Imperial Japanese Army. Their new perimeter would start in Burma, where they would hold the line against Slim’s 14th Army, then attack into India and cut the Ledo/Burma road that supplied the Chinese. The rest of the perimeter would extend to Singapore, the strategically and economically important Dutch East Indies, Dutch New Guinea, the Philippines, and finally the Palau, Marianna, and Bonin Islands. There the Allies were to be stopped.
For a few months they discretely “redeployed” capital ships under the guise of preparing for a massive counterattack. By January 1944, they had no choice but to strip the forward bases of anything that could be used. Everything to the south and east of this line was to be abandoned. But the submarine threat and the lack of industrial output meant that there was only room for irreplaceable equipment, not troops. The remaining garrisons were told they would receive no more support and they were on their own. On 22 February 1944, the last convoy left Rabaul, once the most important Japanese base in the South Pacific, taking with it the last of its vital equipment, and never to return.
300,000 isolated Japanese soldiers, sailors and marines were abandoned to their fate, and left to fight or starve to death