Chapter I:
During the years between the end of World War I and the beginning of World War II there were always a few officers at work in Washington on the war plans of the Army and Navy. It was the duty of these officers to study situations that could suddenly arise in which the federal government might resort to the use of armed force, and to propose the courses of action that the services should be ready to take. From tune to time the War or Navy Department approved one of these studies as a war plan to guide the special plans and preparations of their staffs and operating commands. Several war plans were prepared jointly and approved by both departments for the common use of the Army and Navy.
During these years national policy was deeply influenced by popular beliefs ,relating to national security which had in common the idea that the United States should not enter into military alliances or maintain military forces capable of offensive operations. , National policy provided a narrow basis and small scope for military planning. During the 1920's the United States entered into international agreements to limit naval construction and to "outlaw" war. In the 1930's the United States experimented with the use of diplomatic and economic sanctions to discourage military aggression, and with legislation intended to keep the United States out of European and Asiatic wars. As international tension increased, President Franklin D. Roosevelt became more and more anxious over the diplomatic and military weaknesses of the United States. But it was not until the summer of 1939 that he took official notice of the joint war plans of the Army and Navy. The planners had just finished a study of the situations in which the United States might enter a war begun by Germany and Japan. By the outbreak of World War II in September 1939, the Army and Navy were hard at work on their first strategic plan for coalition warfare, on the hypothesis that the United States would join the European colonial powers in defending their common interests in the western Pacific against attack by Japan.
The Study of War With Japan
The strategy of a war in the Pacific with Japan was the only part of American military planning that had a long, continuous history. Since the early 1900's it had been evident that the United States Government, if it should ever oppose Japanese imperial aims without the support of Great Britain and Russia, might have to choose between withdrawal from the Far Fast and war with Japan.
After World War I the Army and Navy paid more and more attention to just this contingency as a result of the resurgence of Japanese imperialism, the exhaustion of Russia and its alienation from the Western world, the disarmament of the United

States, and the withdrawal of the United States from its temporarily close association with the European colonial powers. In the Pacific the Japanese had strengthened their position early in World War I by taking the Marianas, Carolines, and Marshalls. Japanese control of these strategically located islands was confirmed in 1920 by a mandate from the League of Nations. After the Washington naval treaty of 1922, the United States began to fall behind Japan in the construction of new naval vessels.
The Army and Navy watched with growing anxiety during the 1930's as Japan acquired control of Manchuria, seized strategic points on the north China coast, and forbade access to the mandated islands. The Japanese Government acted with growing confidence, in the belief that the United States, the Soviet Union, and the European colonial powers were not likely to take concerted action against its expansion. In 1933 the Japanese Government exhibited this confidence by withdrawing from the League of Nations in the face of the Assembly's refusal to recognize the Japanese puppet regime in Manchuria. Having taken this step with impunity, the Japanese Government served notice, in accordance with the 1922 treaty terms, of its intention to withdraw from the 1922 and 1930 naval limitations agreements, both of which accordingly expired in 1936.
By the mid-1930's the American military planners had finally concluded that Japan could be defeated only in a long, costly war, in which the Philippines would early be lost, and in which American offensive operations would take the form of a "progressive movement" through the mandated islands, beginning with the Marshalls and Carolines, to establish "a secure line of communications to the Western Pacific." 1 The planners then faced the question of whether the makers of national policy meant to run the risk and incur the obligation of engaging in such a war. The Mate Department had not relaxed its opposition to Japanese expansion on the Asiatic continent. This opposition, for which there was a good deal of popular support, involved an ever-present risk of armed conflict.
After the passage of the Philippine Independence Act (Tydings-McDuffie bill) in 1934, the belief gained ground in the War Department that the United states should not run the risk nor incur the obligation of fighting the Japanese in the western Pacific. When the question finally came up in the fall of 193;1, the Army planners took the position that the United States should no longer remain liable for a fruitless attempt to defend and relieve the Philippines and the costly attempt to retake them. The senior Army planner, Brig. Gen. Stanley D. Embick, stated the case as follows:
If we adopt as our peace-time frontier in the Pacific the line Alaska-Hawaii-Panama:
a. Our vital interests will be invulnerable.
b. I n the wont of war with Japan we will be free to conduct our military (including

naval) operations in a manner that will promise success instead of national disaster.2
This view was entirely unacceptable to the Navy planners. The whole structure of the Navy's peacetime planning rested on the proposition that the fleet must he ready to take the offensive in the Pacific should war break out. It was out of the question for the Navy planners to agree to give up planning offensive operations west of Hawaii. For two years the Army and Navy planners engaged in intermittent dispute over the military policy on which they should base plans for fighting a war with Japan. The Chief of Staff of the Army, General Malin Craig, evidently shared the views of his planners, but he was either unable or unwilling to have the dispute brought before the President for decision.3  
The weakness of the American position in the Far Fast and the danger of war steadily became more apparent. The expiration of the naval limitations agreements re-opened the possibility that the United States might fortify Guam, thus partially neutralizing the Japanese position in its mandates (which were presumably being fortified, since it had become impossible to gain access to them or much intelligence about them). The Congress refused to authorize this step. In the summer of 1937 the Japanese began an undeclared war in China--the "China Incident"--bringing closer the moment at which the United Mates must choose either to accept or contest Japanese aims.
The planners finally came to an agreement by avoiding the disputed issues. Early in 1.938 they submitted a revised plan, which the joint Board ; the Chief of Staff and the Chief of Naval Operations) and the Secretaries at once approved. The Navy planners agreed to eliminate references to an offensive war, the mission of destroying Japanese forces, and the early movement of the fleet into the western Pacific, in return for the agreement of the Army planners to eliminate the proviso that any operations west of Midway would require the specific authorization of the President. The revised plan gave no indication of how long it should take the Navy to advance into the western Pacific and tacitly recognized the hopeless position of the American forces in the Philippines. Those forces retained the basic mission "to hold the entrance to MANILA BAY, in order to deny MANILA BAY to ORANGE [Japanese] naval forces," with little hope of reinforcement.4

Alternatives in a World War
The rising danger of war with Japan was in keeping with the growing insecurity of all international relations during the 1930's. Every nation with which the United States had extensive political and economic: relations was affected by the prolonged economic crisis of the 1930's and by its social and political consequences. In Europe the principal phenomena were the renascence of German military power and aims under the -National Socialist Party and the passivity of the British and French Governments, paralyzed by conflicts in domestic politics, in the face of the new danger.
In 1938 the American military staff extended the scope of war planning to take account of the reassertion of German imperial aims. The immediate cause was the German demand made on Czechoslovakia in September 1938 for the cession of a strip of territory along the border. The area contained a large German-speaking minority, among whom the Nazis had recently organized an irredentist movement in order to create a pretext for German intervention. The area also contained strong border defenses and a highly developed munitions industry, which made it by far the most important area, for military purposes, in Central Europe.
The German ultimatum, backed by German troops mobilized on the border of Czechoslovakia, amounted to a demand that Germany be recognized and accepted as the dominant military power on the Continent-an evident objective of German domestic and foreign policy since Hitler's accession to power in 1933. After consolidating his power at home, Hitler had accelerated German rearmament, reintroduced military conscription, and remilitarized the Rhineland. Thereafter, by forming an alliance with Italy (already dedicated to a program of tyranny, autarchy, chauvinism, and conquest), and by intervening in Spain and absorbing Austria, he had greatly strengthened the German position and weakened the British and French position in Central Europe and the Mediterranean. To complement these military measures he had sought to neutralize opposition abroad by subsidizing parallel political movements, propaganda, and treason and by negotiating bilateral trade arrangements and cartel agreements.
The British and French Governments, weighing the value of the French alliance with Czechoslovakia and the Soviet Union against their own unpreparedness, military and political, had an extremely hard decision to make. After conferences at Berchtesgaden and Munich, Prime Minister 1ille Chamberlain, with the concurrence of Premier Edouard Daladier, agreed not to oppose the German ultimatum. In so doing, they went far to relieve Germany of the fear of having to fight again on two fronts at one time, for in abandoning Czechoslovakia, which upon the loss of the Sudeten area became indefensible, they greatly weakened the military alliance between France and the Soviet Union. Their decision constituted admission and resulted in the aggravation of the political and military weakness of their countries.
After Munich the prospect of a general European war, which had briefly seemed imminent, receded, but the military situ-

ation in Europe was far more threatening than before. President Roosevelt warned the American people that the danger had a bearing on the security of the United Mates and warned the world at large that the United States recognized this danger and would act to meet it, specifically in the Western Hemisphere.5 His declaration carried very little weight at home or abroad. Neither tile news reports nor the warnings that accompanied them greatly affected, except perhaps to confirm, the widespread American belief, shared and expressed by many well-known men, that the United States need not and should not accept the risk of being drawn into another European war. 6 The President could neither change nor ignore that belief. His military subordinates were as well aware of that fact as his political adherents and opponents and the heads of foreign governments. Yet his evident concern licensed, as the events obliged, the military planners to study, within narrow limits, the possible effects on American security of action by German, with the support of Italy and, perhaps of Spain, in conjunction with action by Japan.
Early in November the Joint Board sent the joint Planning Committee (JPC) the following problem to study: . . . the various practicable courses of action open to the military and naval forces of the  United State. in the event of  a) violation of the Monroe Doctrine by one or more of the Fascist powers, and (b) a simultaneous attempt to expand Japanese influence in the Philippines.7  
The planners studied the problem during the winter of 1938-39, the winter during which the Germans annexed the rest of Czechoslovakia. They presented the result, five and a half months later, in April 1939. Their final report listed the advantages Germany and Italy would stand to gain by a violation of the Monroe Doctrine and described the form it could be expected to take. What Germany and Italy would try to do would be to establish "German and Italian regimes that would approach or attain the status of colonies," with the usually alleged attendant advantages-increased trade, access to raw materials, and military and naval bases. They might acquire bases "from which the Panama Canal could be threatened to an extent that pressure could be exerted on United Mates Foreign Policies." The probable means of German and Italian aggression with these objectives would be "direct support of a fascist revolution" The planners concluded that the danger of this kind of offensive action in the Western Hemisphere would exist only (1) in case Germany felt assured that Great Britain and France would not intervene; and (2) in case Japan had already attacked the Philippines or Guam, and even then only in case the United States had responded  to the Japanese attack by a counteroffensive into the western Pacific.
The planners considered it quite unlikely that in the near future Great Britain and

France would give Germany the necessary assurances or that Japan would decide to attack. They nevertheless believed that the kind of problem posed-resulting from concerted aggression by Germany, Italy, and Japan-was one that should be taken into account in future planning, and recommended steps to be taken "to overcome salient deficiencies in our readiness to undertake the operations that might be required." 8

This study having been approved by the joint Board, the planners proceeded to distinguish the principal courses of action open to the United States as a belligerent in the crises that seemed most likely to develop out of future German and Japanese moves and the delayed responses thereto in American foreign and domestic policy. They proposed to assume that to begin with "the Democratic Powers of Europe as well as the Latin American States" would be neutral. But they also proposed to set forth in each situation that might arise "the specific cooperation that should be sought" from these powers as allies or as neutrals and, moreover, to provide for possible action in case the United States "should support or be supported by one or more of the Democratic Powers," that is, by Great Britain or France. 9  

This projected series of new plans had a new title-the RAINBOW plans that aptly distinguished these plans from the "color" plans developed in the 1920's for operations against one or another single power (the plans for war with Japan, for example, were called ORANGE). The most limited plan (RAINBOW 1) would provide for the defense of the Western Hemisphere south to the bulge of Brazil (10 south latitude) the Western Hemisphere being taken to include Greenland (but not Iceland, the Azores, or the Cape Verde Islands) to the east, and American Samoa, Hawaii, and Wake (but not Guam or the Philippines) to the west. Two other plans would provide alternatively for the extension of operations from this area either to the western Pacific (RAINBOW 2) or to the rest of South America (RAINBOW 3) . The directive also called for modification of the first three plans under the contingency (RAINBOW 4) that Great Britain and France were at war with Germany and Italy (and possibly Japan), in which case it was assumed that the United States would be involved as a major participant.10

After a few weeks' work under these terms of reference, the joint Planning Committee concluded that the requirements under this fourth contingency w " different and divergent" from t in e three basic plans that separate plans would have to be made to deal with them. The planners pointed out that in case of war among the great powers-using current available forces-with Great Britain and France, and possibly the Soviet Union opposing Germany, Italy, and Japan, and possibly Spain, German and Italian operations in the western Atlantic and in South America would be very much restricted in scope, whereas Japanese operations in the Pacific might be very much extended in scope. The Japanese, if unopposed, might seize

. . . the English and French Islands in the South Pacific, east of 180th meridian, such as

Marquesas, Societies, Samoa, and Phoenix Islands, as well as the extensive English and French possessions in the Western Pacific, and the United States possessions in the Pacific.
The committee therefore recommended that in addition to the three plans against the contingency of a war with Germany, Italy, and Japan, two plans, rather than one, should be drawn up to (:over a war in which not only the United States but also Great Britain and France were involved against that coalition.
One plan should provide for a large-scale American effort against Germany; the other for a large-scale American effort against Japan. The committee stated these two cases as follows:
The United States, England, and France opposed to Germany, Italy, and Japan, with the United States providing maximum participation, in particular as regards armies in Europe.
The United States. England, and France opposed to Germany, Italy, and Japan, With the United States  providing maximum participation in continental Europe, but maintaining the Monroe Doctrine and carrying out allied Democratic Power tasks in the Pacific.
The latter of these contingencies, which the Navy staff had independently been discussing with the British naval staff in ever more definite terms since 1934, the committee considered to be peculiarly important, as involving problems "that might conceivably press more for answers" than all but the first, most limited basic plan (for defending the Western Hemisphere north of 10 south latitude). The committee therefore recommended that it should be placed second in order of priority in the list of five situations to be studied, explaining:
Whether or not we have any possible intention of undertaking a war in this situation, nevertheless we may take measures short of war, and in doing so should clarify the possible or probable war task that would be involved. 11
On 30 June 1939 the joint Board approved the recommended changes, including the recommended change in order of priority. 12 The revised description of the Rainbow plans, as approved, read as follows
a. joint Army, and Navy Basic War Plan Rainbow No. l:
Prevent the violation of the letter or spirit of the Monroe Doctrine by protecting that territory of the Western Hemisphere from which the vital interests of the United States can be threatened, while protecting the United States, its possessions and its sea-borne trade. This territory is assumed to be any part of the Western Hemisphere north of the approximate latitude ten degrees south.
'This plan will not provide for projecting U. S. Army Forces farther south than the approximate latitude ten degrees south or outside of the Western Hemisphere.
b. Joint Army and Navy Basic War Plan Rainbow No. 2:
( 1 ) Provide for the missions in a.
( 2 ) Under the assumption that the United States, Great Britain. and France arc acting in concert, on terms wherein the United States does not provide maximum participation in continental Europe, but undertakes, as its major share in the concerted effort, to sustain the interests of Democratic Powers in the Pacific, to provide for the tasks essential to sustain these interests, and to defeat enemy forces in the Pacific.

c. Joint Army and Navy Basic War Plan
Rainbow No. 3:
(1) Carry out the missions of the Joint Army and Navy Basic War Plan--- Rainbow No. 1.
(2) Protect United States' vital interests in the Western Pacific by securing control in the Western Pacific, as rapidly as possible consistent with carrying out the rapidly in a. d. Joint Army and Navy Basic War Plan Rainbow No.4:
(1) Prevent the violation of the letter or spirit of the- Monroe Doctrine by protecting all the territory and Governments of the Western Hemisphere against external aggression while protecting the United States, its possessions, and its sea-borne trade. This Plan will provide for projecting such U. S. Army Forces as necessary to the southern part of the South American continent or to the Eastern Atlantic.
e. Joint Army and Navy Basic War Plan
Rainbow No. 5:
(1) Provide for the missions in a.
(2) Project the armed forces of the United States to the Eastern Atlantic and to either or both of the African or European Continents, as rapidly as possible consistent with carrying out the missions in a above, in order to effect the decisive defeat of Germany, or Italy, or both. This plan will assume concerted action between the United States, Great Britain, and France. 13
Allied Operations in the Pacific
This analysis of possible courses of action was easily adapted to the situation that existed for several months after the outbreak of war in Europe in September 1939. When the German Army moved into Poland the planning staffs were already working full time on plans for a war in the Pacific against Japan, in which the United States would be allied with the European colonial powers, within the terms of reference of RAINBOW 2. 14 Work on RAINBOW 2 went on during the fall and winter of 1939 and into the spring of 1940.15 During this time-the period of the German-Soviet conquest and partition of Poland, the Soviet war against Finland, and the "sitzkrieg" on the Western Front-Rainbow 2 seemed to be, as the planners had expected it to be, the war plan most appropriate to the military situation. Great Britain and France were at war with Germany and its allies. They controlled northwestern Europe and northern Africa. Their fleets controlled the Atlantic and-though less securely-the North Sea and the Mediterranean. It could be assumed that only a Japanese attack would involve the United States in war, and that, in case of Japanese attack, the United States, while taking precautions in the Western Hemisphere, would set out-with the blessings of the British and French Governments-"to sustain the interests of Democratic Powers in the Pacific, to provide for the tasks essential to sustain these interests, and to defeat enemy forces in the Pacific. 16  
As the Joint Planning Committee had foreseen, planning against this contingency

was indeed complicated. The planners faced a war far more complex than that envisaged in the ORANGE plan, with an immensely greater range of possible Japanese operations to consider, and with very difficult problem; of harmonizing American operations with those of the forces of Australia, New Zealand, and the European powers concerned.
The planners first had to assume how far the Japanese would have extended their control south and west at the moment the United States and the other "Democratic: Powers" began to act. The Navy planners at the outset set up three alternative hypotheses. The first was that Japan would not have begun moving southward from Formosa. In that case the U. S. Fleet might move to Manila Bay, "with certain groups visiting Singapore, Kamranh Bay, and Hong Kong." Ground forces might be moved to the western Pacific at the same time or later. The Navy planners thought that these acts might prevent Japanese moves southward, and hence prevent a war in the Pacific. The second hypothesis was that Japan had taken Hong Kong, Kamranh Bay, and begun operations in the Netherlands Indies, that the United States would react by moving forces to the far Pacific, and that the Japanese in turn would begin operations to seize Guam and the Philippines. The third hypothesis was that the Japanese would already have control of the Netherlands Indies and would have forces in position t0 Isolate Singapore and take the Philippines. In this case, as the Army planners pointed out, "the principal advantages of Allied participation will have been lost and the problem becomes essentially that of an Orange War." 17
Since extensive operations in the Southwest Pacific seemed less likely under the first and third hypotheses, planning for Rainbow 2 proceeded on the second hypothesis . . . that Japan has captured Hong Kong: occupied Kamranh Bay; dominates the coast of  Indo China and has initiated operations against the Dutch East Indies, including British Borneo, and that Japan has force; available to undertake Immediate operations against Guam and the Philippines when it becomes evident that armed forces of the United Status will be moved in strength to the Western Pacific.18
In this ease, the main initial movement of American forces in the Pacific would be to Singapore and the East Indies. The Army planners emphasized that to retake the positions occupied by the Japanese would be a slow, step-by-step process, and that " even day's delay" in the arrival of American forces would allow the Japanese to effect establishments that may require months to dislodge." As a result, they continued, it might be necessary to defer operations against the mandated islands and to take into account the danger that the Japanese might cut the lines of communication through the South Pacific, unless the extension of the Japanese lines might have forced them greatly to weaken their forces in the mandates. To avoid this danger, American forces would move to Singapore, not by way of the Philippines, but by way of the South Pacific : Canton, Phoenix

Islands), Suva ( Fiji Islands), Simpson Harbor ( Rabaul ) , Molucca Sea, and Java Sea.19 These forces would be supplied over the long route across the Atlantic, around the Cape of Good Hope, and across the Indian Ocean, although the planners expected that the United States could and would send air reinforcements by way of the South Pacific, either along the route traced above or by a more southerly route from Hawaii to Palmyra and Christmas, Canton and Hull islands, Suva, New Caledonia, New Guinea, Port Darwin, and Surabaja ( Java). In this war, the joint tasks, in concert with British, French, and Netherlands forces, would be to establish U. S. forces in the East Indies area, obtain control of the area, and drive the Japanese out. The peace settlement would entail Japanese evacuation of Hong Kong, the Philippines, and Guam.20
In trying to lay down assumptions as to the military position of Japan at the time when the United States would act, the planners also ran directly into a second problem---uncertainty as to the course of action of the European colonial powers. By April 1940 the planners had gone about as far as they could without having an explicitly approved basis for assuming what the European colonial powers would do. This, although not prerequisite to planning for joint action by the U. S. and British Navies- --already well advanced on the basis of the President's implicit approval- --was a sine qua non even of a hypothetical exploration of the politically explosive question of sending U.S. Army  forces to defend European colonial possessions in the Far East. The planners had therefore no choice but to recommend that the United States Government should propose conversations with the British, French, and Netherlands authoritarian "as soon as the diplomatic situation permits." They also recommended that the diplomatic conversations "should be conducted in coordination with representatives of the Chief of Staff of the Army and the Chief of Naval Operations. 21
It was logical for the planners to expect that the role of the United States in coalition strategy would be to protect and, if necessary, defend and re-establish its own position and that of the European powers in the western Pacific. The planners had selected this hypothesis for study after taking into account the physical facts of the military situation at the beginning of World War II--order of battle, distances, and so on. So far as it went, their analysis of the American role was correct, and it was to play an important part in strategic planning throughout World War II.

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