Factors Determining the Nature of the Succeeding Campaign

After the engagements of 1942, certain basic lessons of combat in the Pacific theater had been learned. It appeared that the widely spread Japanese positions could be bypassed or captured, provided that air superiority in the necessary areas was achieved, and provided the required naval support, adequate assault craft, properly trained troops, and full logistics were available. Major preparations were required before decisive advances could be undertaken. In the meantime, however, unremitting pressure could be kept on the Japanese.

Due to the geography of the Empire, the Japanese ground forces depended for their effectiveness upon overseas support in all areas except the main home islands, and even there, overseas imports of raw materials were required. In China, Korea, and Manchuria, an overwater lift to the mainland was involved, and shipping was employed in the supply of troops in Malaya, Burma, and continental regions of the southwest. The islands of the eastern perimeter were completely dependent on supply by sea. Deployed as the Japanese ground forces were on detached land masses, dependent on inadequate shipping, their defeat was necessary only at points of United States choosing. The bulk of them could be bypassed.

The Japanese Navy, which included two 64,000 ton battleships of great fire-power and speed, had lost both operational freedom and striking power due to its limited carrier-based air strength. By late 1943, the United States had available sufficient carriers for clear-cut superiority in the air, and had added to the fleet sufficient modern heavy ships to offer reasonable protection against the Japanese surface strength were it to be committed under bad weather or other conditions limiting the degree to which our superiority in the air could be brought to bear. The ability to destroy the Japanese surface forces, if they were committed, was essential. Furthermore, their destruction would increase the freedom and ease of our further advances.

The limitations imposed by geography and the range of Japanese land-base planes made it impossible for the Japanese to achieve sufficient mobility of their land-based air forces to concentrate their full air strength against us at any crucial point, prior to the invasion of the Philippines and Okinawa. Most of the island atolls were too small to support the necessary air fields, and in New Guinea, the Solomons and the Marianas, logistic, air field construction and ferrying problems made such concentration impossible. Even within the limits so imposed, poor Japanese staff work and tactics resulted in piecemeal employment of their available air strength. Over and above these weaknesses, Japanese aircraft production, pilot training and maintenance were so far behind our own that it was evident that general air superiority over the Japanese could be achieved. This objective received first priority.

The Japanese shipping target was immediately available. In the first year of the war, submarines, capable of long-range offensive action inside the Japanese perimeter, sank more than 10 percent and air planes 4 percent of the merchant ship tonnage which Japan possessed at the start of the war. The strangulation of Japanese overwater movement, thus begun, could be continued both by the submarine and by attack from the air.

Japanese industry and her home population would not be within effective striking distance of United States long-range bombers until bases within 1,500 nautical miles of Japan could be secured.

An advance to strategic positions across the Pacific would give us bases from which to complete the interdiction of Japan's overwater shipping, to mount large scale air attacks against the Japanese home islands, and to prepare for an invasion of the home islands themselves.