Battle of Saipan - Background

Background

In the campaigns of 1943 and the first half of 1944, the Allies had captured the Solomon Islands, the Gilbert Islands, the Marshall Islands and the Papuan Peninsula of New Guinea. This left the Japanese holding the Philippines, the Caroline Islands, Palau Islands and Mariana Islands.

It had always been the intention of the American planners to bypass the Carolines and Palaus and to seize the Marianas and Taiwan. From these latter bases communications between the Japanese homeland and Japanese forces to the south and west could be cut. In addition, from the Marianas Japan would be well within the range of an air offensive relying on the new B-29 Superfortress long-range bomber with its operational radius of 1,500 mi (2,400 km).

While not part of the original American plan, Douglas MacArthur, commander of the Southwest Pacific Area command, obtained authorization to advance through New Guinea and Morotai toward the Philippines. This allowed MacArthur to keep his personal pledge, made in his "I shall return" speech, to liberate the Philippines, and also allowed the active use of the large forces built up in the southwest Pacific theatre. The Japanese, expecting an attack somewhere on their perimeter, thought an attack on the Caroline Islands most likely. To reinforce and supply their garrisons, they needed naval and air superiority, so Operation A-Go, a major carrier attack, was prepared for June 1944.