Downfall Strategic Plan: Concept Excerpt
“This plan of campaign visualizes attainment of the assigned objectives by two (2) successive operations, the first to advance our land-based air forces into Southern KYUSHU in order to support the second, a knock-out blow to the enemy’s heart in the TOKYO area. The operations are continued and extended until such time as organized resistance in the Japanese Archipelago ceases.
The concept of the OLYMPIC operation visualizes entry into Southern KYUSHU by major joint overseas landing operations after intensive air preparation. Preparatory air operations include assaults by Carrier Task Groups and prolonged action by land-based elements operating in force from the RYUKYUS and MARIANAS. Initial assaults seize and develop the KAGOSHIMA WAN and ARIAKI WAN as ports of entry. The area is occupied as far north as the general line TSUNO-SENDAI to block mountain defiles and prevent hostile interference with our operations.
These operations are expected to require fourteen (14) to seventeen (17) divisions with appropriate supporting troops, drawn from forces available in the PACIFIC with minimum use of redeployed elements. Forty (40) land-based air groups and naval elements for blockade and direct support are established for support of the CORONET operation.
Concept of the CORONET operation visualizes a major joint assault supported by the massed air and naval power in the PACIFIC, to destroy hostile forces and seize the TOYKO-YOKOHAMA area.
Initial operations establish local air support and drive into the KANTO PLAIN from outlying beaches, while defenses of the approaches to the TOKYO WAN and Northern SAGAMI BAY are reduced by intensive naval and air action. Forces are built up by subsequent landings, and operations are continued to the occupation of the TOKYO-YOKOHAMA Area and the KANTO PLAIN.
These operations are expected to require initially twenty-five (25) divisions with appropriate supporting troops, drawn from PACIFIC resources remaining after OLYMPIC, augmented by redeployment. Land-based air elements and naval forces are established as required to support operations in central and northern JAPAN to conclusion, and to operate against the Asiatic Mainland as necessary. Logistic facilities are established in the TOKYO WAN to support consolidation of central and northern JAPAN.
It is estimated that the maximum air garrison will not exceed fifty (50) groups, which figure is subject to revision as situation develops.
Occupation of the KANTO PLAIN is followed by such operations from the OLYMPIC and CORONET areas as may be necessary to terminate organized resistance in the Japanese Archipelago.
If required by the situation prior to CORONET, intermediate operations are conducted to establish advance fighter element in Southern SHIKOKU or Southeast HONSHU to cover our advance.
In event forces allocated OLYMPIC operation are insufficient to accomplish tasks assigned, build-up in OLYMPIC area from elements earmarked for CORONET is continued at the rate of (3) divisions per month beginning about (X plus 30) with supporting troops as required by the situation. The CORONET operation is adjusted accordingly.
In event forces allocated CORONET operation are insufficient to successfully perform tasks assigned, build-up from War Department Strategic Reserve is continued direct to the objective area at a rate of four (4) divisions and appropriate supporting troops per month beginning about (Y plus 90) to a strength required by the situation.
The United States Pacific Fleet conducts the amphibious phases of the operations, supports ground action after landing and covers the operation by naval and air action against hostile supporting air, naval, and land forces.
The Twentieth Air Force, initially employed on strategic targets in coordination with long-range land based and carrier-based air action, tactically supports as necessary the amphibious and ground phases of the respective assaults.
The Commanding General, CHINA Theater cooperates by conduct of diversionary and containing operations within the limits of his capabilities.
Should RUSSIA enter the war prior to completion of the CORONET assault phase, diversions from forces herein allocated may be directed by the Joint Chiefs of Staff in orer to establish and maintain a sea route to Eastern SIBERIA. In this event, the operations outlined abouve are conducted with minimum alteration, such adjustments being made in timing as may be require to procure essential replacements for forces committed.”