The Advance Across the Pacific

Such was the situation when the United States began its widespread offensive. While major preparations were still in progress, and the heavy attrition of the Solomons and eastern New Guinea campaign was chewing up Japan's best air groups and depleting her shipping and supplies, the first long-range moves in the advance across the Pacific were undertaken. These began unostentatiously with the assault against Attu, on the northern flank of the Japanese defense perimeter in May 1943. On the southern flank, the offensive continued with an advance to Munda in June, to Salamaua, Lae, and Finschafen on New Guinea in September, and Bougainville in November 1943. In the Central Pacific it began with the assault on the Gilbert Islands in November 1943.

Thereafter, the amphibious advance toward Japan continued over two routes. One was up the north coast of New Guinea to the Philippines, the other across the Central Pacific through the Marshalls to the Marianas and Palau and then subsequently on to Iwo Jima and Okinawa. Basically, the advance was for the purpose of projecting United States power to points which cut Japan's supply lines to the south and were within striking range of the Japanese home islands. Objectives were seized for one or more of four purposes: To provide forward air fields so that shore-based aircraft might maintain and project forward United States control of the air; to furnish advance bases for the fleet; to secure land areas for the staging of troops in succeeding advances; and, in the case of the Marianas, to provide bases for long-range air attacks on the Japanese home islands.

In the New Guinea area it continued to be possible to choose objectives for our advance where the enemy was weak, to seal off these objectives from enemy reinforcement and cover advances to them with land-based air, and, in certain instances, to supply the operation entirely by air. Marilinan, Nadzab and other inland bases on New Guinea, which eventually had complements as large as 25,000 men, were occupied, supplied and later moved forward entirely by air. The range of these advances was limited to the combat radius of fighter aircraft.

For long-range amphibious advances against strongly defended positions a typical pattern developed. Japanese bases flanking the United States objective were smothered by a concentration of air power. Such bases as were within reach were hammered by shore-based air. Carrier-based air and available shore-based air softened the area to be occupied, and as the amphibious force moved up, fast carriers advancing beyond the objective struck swift blows at all positions which could threaten the objective area. With close air support from both escort and fast carriers and a concentration of gunfire from combatant ships of the support force, an amphibious assault over the beaches was made. The objective was secured under air support and cover from the carriers, which were not withdrawn until air fields ashore could be prepared and activated.

The amphibious steps along the two principal lines of advance toward Japan were well timed and mutually supporting, even though concentration on one line might have been more rapid. The losses inflicted at Rabaul, primarily by land-based planes from the Solomons and New Guinea, forced the Japanese to the decision not to support their garrisons in the Gilberts, were they to be attacked. The Central Pacific advance into the Gilbert and Marshall Islands in late 1943 and early 1944, and the threat of a fast carrier task force strike against Truk, which eventuated in February 1944, cleared the Japanese Fleet from the New Guinea flank and assisted the move into the Admiralties in March 1944 and the long step up the coast of New Guinea to Hollandia in April 1944, which was followed by a further advance to Wakde and Biak in May 1944. When the Japanese attempted reinforcement of northern New Guinea, the Central Pacific advance into the Marianas in June 1944, forced the abandonment of the operation. The Japanese committed their carriers in the defense of the Marianas, and lost in the Battle of the Philippines Sea practically all their carrier-based air groups sufficiently trained for combat, as well as three carriers sunk. Noemfoor was taken while the Japanese were preoccupied in the Marianas. Landings on Morotai were timed with those in the Palaus.

While the landings in the Palaus were in progress, the fast carrier task force struck Japanese aircraft, air fields and shipping in the Philippines. Preliminary to the Leyte operation, the fast carrier task force with a concentration of more than 1,000 planes attacked Okinawa, Formosa and the Philippines, exacting a large toll of Japanese air power. B-29 strikes from China against air installations on Formosa supported this operation. The landing at Leyte Gulf in the Philippines was correctly assessed by the Japanese as their last opportunity, short of a defense of the Japanese home islands, to throw in all their available forces to check the United States advance in a decisive engagement.

Three days after the landing at Leyte they committed their entire fleet in a three-pronged attack. The plan contemplated that a carrier force advancing from the north would draw off our main strength, while heavy surface forces approaching through Surigao and San Bernardino Straits and covered by Japanese Army and Navy planes from airfields in the Philippines would destroy our transports and supporting strength off the landing beach. The Japanese strategy succeeded in drawing off our main strength to the north. The southern Japanese force was destroyed in a night surface engagement in Surigao Straits. Four carriers in the northern force were sunk off Luzon. Although one of its super-battleships had been sunk by torpedo plane attack, the central force penetrated close to our transports still possessed of overwhelming surface strength. The Japanese commander of the central force testified to the Survey that lack of expected land-based air support and air reconnaissance, fear of further losses from air attack, and worry as to his fuel reserves induced him to withdraw. As a result of this decision to retire, the Japanese failed to secure the objective for which catastrophic losses had been risked and suffered by the other two Japanese forces.

In the ensuing actions in the Philippines, the Japanese lost all the troops and supplies deployed there, plus three and one-half divisions sent in from China and Manchuria. In the Philippines campaign as a whole they committed and lost 9,000 planes. On 1 March 1945, the Japanese decided to send no further supplies to their ground forces outside of the home islands. Except for delaying actions they had been forced to concentrate solely on defense against invasion.

While the liberation of the Philippines was being completed, the Central Pacific forces made the difficult moves into Iwo Jima and Okinawa.