Truk was part of the Japanese Mandated Islands ceded to Japan in 1919. A major fleet anchorage was created there soon after occupation, and over the next twenty-five years the Japanese used Truk as their main base of operations for the Southern Pacific. Admiral Isoroku Yamamoto left for his fateful rendezvous with death over Rabaul from the Combined Fleet Headquarters on Truk.
The attack on Truk was dreaded by the pilots of the fast carriers. Intelligence believed that the island's defenses were very powerful. To facilitate the advance on Japan, the United States Navy decided to reduce the garrison by air attack, especially the potent fighter and bomber force. The Americans hoped this would obviate the need for a ground invasion. They also hoped to destroy any shipping in the island's anchorage. In the first dedicated use of lifesaver submarines, the USS Tang (SS-306) picked up 22 downed aviators, the highest record for a single submarine during the war. Later in 1944 the USAAF would repeatedly attack Truk with B-24 Liberators of the Fifth Air Force.