When Guadalcanal was secured, the Solomons were still largely held in Japanese hands or deserted. To the north, the major Japanese base on New Britain, Rabaul, could control the entire area with its large complement of aircraft and its excellent naval anchorage. The Allies held Guadalcanal, with its expanding airfield, and were beginning to grow in strength all through 1943.
During the Battle of Santa Cruz in October 1942, the US Navy lost the USS Hornet, reducing their carrier strength to almost nothing. The USS Enterprise, damaged in combat, was the only operational carrier available. She would face IJN Zuikaku and IJN Shokaku alone for a time. They were the only survivors of the Japanese fleet that attacked Pearl Harbor.
Landing on Rendova in June 1943, the Allies fought through Bougainville and surrounding islands during the first half of the year. So many ships were sunk, the channel down the center of the island chain became known to the Allies as "Ironbottom Sound." The series of engagements around and in the Solomons were intense, costing both sides large numbers of ships, aircraft and men.
The Japanese were not faring any better, losing ships and planes that they could not replace. Far more costly was the loss of men. The Imperial Japanese Navy was choosing to forego parachutes and send away their lifeboats with the enlisted men. Yamamoto had to issue a directive reminding his officers and men that planes and ships could be replaced, and they could not. The trained officer corps was bleeding to death.
It a sad fact of combat that the highest casualties fall upon the junior officers and noncommissioned officers. The rate of captains and admirals going down with their ship, demonstrating their loyalty to the Emperor, was wreaking havoc on his least available asset, his junior officers.
Among the Japanese there was a feeling that without victory there must be death. Admiral Isoroku Yamamoto, hailed as a tactical genius, was considered the most important man. Again, without knowing that the Allies were reading Japanese codes, Yamamoto’s visit to the forward area of Rabaul was detailed in a transmission and sent to all stations. When the US Naval Intelligence got a hold of the schedule, they knew they had an opportunity that might never come again.
Nimitz, when given the option of assassinating his Japanese counterpart, decided he had to seek higher authority. The entire intelligence operation might be compromised if the Japanese realized that Yamamoto’s schedule was decoded. Admiral Ernest King, the highest-ranking officer in the Navy, decided there had to be Presidential approval. Roosevelt signed the order.
On April 18, 1943, P-38 Lightning fighters, the aircraft with the longest range, took off from Henderson Field for Rabaul. They flew for hours, and arrived over Rabaul at the same time as the Mitsubishi G4Y Bomber carrying Yamamoto. The actual pilot who shot down Yamamoto is still in dispute. What is certain is that the greatest Japanese naval hero since Togo was shot down, still clutching his samurai sword. The six pilots who were Yamamoto’s escort could do nothing as their leader was shot down. They were given the choice of death in combat, and within six months five of the six were dead.
As part of the policy of "island hopping" the Japanese base on Rabaul was isolated and cut off from reinforcements. It remained in Japanese hands until the surrender in August 1945. At the time of the surrender, only six aircraft were operational. The garrison had not received supplies or reinforcements since early 1944.