'Orange' (i) was the US contingency plan within the 'Color-coded War Plan' scheme for war with Japan (1924/39).

The plan was formulated by the Joint Army and Navy Board, an organisation created in 1903 to consider all matters referred to it by the Secretary of War and Secretary of the Navy requiring inter-service co-operation. Based on the Joint Board’s Strategy of the Pacific, based on Rear Admiral Raymond P. Rodgers’s basic concept of 1911 and finalised on 19 December 1919, the 'Orange' (i) plan was formally adopted on 15 August 1924 on the tacit understanding that the USA would have no allies, and ultimately reflected US Navy rather than US Army thinking in its tacit assumption that the Philippine islands group and other island garrisons in the Pacific could not be held against a Japanese invasion, and were therefore neither to be reinforced nor to receive additional supplies. Such an admission could not be made openly for a host of political and psychological reasons, however, and the plan therefore called for US forces to hold the Manila Bay area in the Philippine islands group as a base until the arrival of naval reinforcements which would relieve the garrison of the Philippines as the first step in an offensive war against the Japanese in the western Pacific.

On the outbreak of war with Japan, therefore, the US Navy’s Pacific Fleet was to concentrate its strength at bases in California, and provide protection against Japanese attacks on the Panama Canal. After the completion of its mobilisation (the ships had only half of their crews in time of peace), the Pacific Fleet was to steam to the western part of the Pacific in order to relieve the US forces holding out on Guam and in the Philippine islands group. After this the Pacific Fleet was to steam to the north for a decisive battle against the Imperial Japanese Navy’s Combined Fleet, and then to blockade the Japanese home islands.

This was in keeping with the theory of Admiral Alfred T. Mahan, a doctrine to which every major navy subscribed before World War II, in which any war was to be decided by engagements between opposing surface fleets.

Rodgers’s concept was closer to the one ultimately used in the Pacific War: a 'leapfrog' campaign to conquer the Marshall islands group and the Caroline islands group held by Japan before the war, the liberation of the Philippine islands group, and the blockade of Japan. Two notable absences from Rodgers’s concept were the decisive battle and the nature of Japanese planning.

US planners failed to appreciate the fact that technological developments in submarines and naval air power had already rendered obsolete Mahan’s doctrine. In particular, they did not understand that aircraft could sink battleships, and that Japan might put the US battleship force out of action at a stroke, as in fact happened during the 'Ai' attack on Pearl Harbor.

In 1935, a navy-sponsored modification called for the capture of islands in the Marshall and Caroline island groups as stepping stones to the Philippine islands group, a tacit admission that the US return to Manila Bay might take years rather than the months first postulated. In 1936, an army-sponsored modification called for the garrison to hold the entrance to Manila Bay rather than the whole of the Manila Bay area, and this modification went some way to recognising the basic impossibility of checking a Japanese invasion of the Philippine islands group.

By 1937, the US Army and US Navy were deadlocked about the strategy to be adopted in the event of any war against Japan. The US Army saw the primary task of its comparatively small forces as the defence of the continental USA, with the Pacific Fleet patrolling no farther to the west that a line through the central Pacific to ensure the safety of the USA’s 'natural strategic frontier' between Alaska and Panama via the Hawaiian islands. The navy was too steeped in the offence-oriented strategic doctrines of Mahan to countenance so defensive an operational role.

The Joint Army and Navy Board entrusted the task of resolving the army and navy differences to Major General Stanley D. Embrick and Rear Admiral James O. Richardson, heads of the army and navy war plans divisions. The two men’s compromise solution was adopted by the Joint Army and Navy Board on 19 February 1938, and this provided for an initial defensive phase (or 'position of readiness') along the lines suggested by the army. At the same time, army and navy forces would prepare for the offensive first against the Japanese mandated territories in the Pacific and second toward the Philippine islands group, which were to be defended around Manila though no mention was made of reinforcement or relief; then there was to be an offensive phase with the war taken to Japan along the lines suggested by the navy.

A number of requirements grew out of 'Orange' (i), including the requirement for a fleet submarine with high speed, long range and heavy torpedo armament: this paved the way to the design and construction of Dolphin with surfaced and submerged displacements of 1,688 and 2,215 tons respectively, surfaced and submerged speeds of 17 and 8 kt respectively, maximum range of 21,600 miles (34760 km), and armament of six 21-in (533-mm) tubes for 18 torpedoes, and one 4-in (101.6-mm) gun. The demand for submarines of this size also drove the development of the problem-plagued Mk XIV torpedo and its troublesome Mk VI exploder, and the considerable expenditure on the development of powerful and compact diesel engines, among them the troublesome Hooven-Owens-Rentschler type.

The Imperial Japanese Navy developed a counter-plan to allow the US Pacific Fleet to sail across the Pacific while using submarines and carrier attacks to weaken it. The Japanese fleet would then attempt to force a battle against the weakened US fleet in a 'decisive battle area' near Japan. Knowledge of 'Orange' (i) also spurred Japan’s demand for a 10/10/7 US/British/Japanese ratio at the Washington Naval Conference, which was considered necessary to provide Japan with superiority in the 'decisive battle area' given the fact that the US had naval commitments in other theatres while Japan did not.

Actual events were very close to the final version of the 'Orange' (i) plan. Carrier battles overshadowed surface action, but the 'leapfrog' campaign was very much as had been anticipated, with progress determined largely by the need to select target islands within range of land-based air power until the US Navy had received sufficient fleet, light and escort carriers to provide cover for its own ships and the landing forces provided by the US Marine Corps sand US Army.

The Imperial Japanese Navy, imbued with the 'decisive battle' doctrine, ignored the vital need for anti-submarine capability. The German and US submarine campaigns against their opponents' merchant shipping demonstrated the need for anti-submarine warfare. While the Allies took extensive measures to combat the threat of German U-boats, the Japanese failed to counter the US submarines which ultimately choked Japan’s industrial production and paralysed its navy. Japan also notably failed to plan or implement any anti-commerce campaign, and the systematic Japanese employment of commerce raiders could have rendered more complex all Allied amphibious operations and more difficult the Allied task of seizing and holding Japanese-held islands.

Soon after the adoption of the revised 'Orange' (i) plan, events in Europe and Asia began to overtake many of the premises upon which the plan was based, and further strategic thinking was diverted to the series of 'Rainbow' plans.

It is worth noting the fact that between the 1898 end of the Spanish-American War and the late 1930s, the army and, to a lesser extent, the navy developed a number of other war plans, identified by the colour coding system, for possible US strategies against several hypothetical war scenarios. The colour-coded plans were officially withdrawn in 1939 in favour of a sequence of five 'Rainbow' plans developed to meet the threat of a two-ocean war against several Axis powers. These plans of the 1920s and 1930s were based on a system of country identification by a code colour: black for Germany (the best-known version of 'Black' being that conceived as a contingency plan during World War I in case France fell and the Germans attempted to seize French possessions in the Caribbean, or launch an attack on the eastern seaboard of the continental USA), blue for the USA as a belligerent, brown for the Netherlands East Indies or, in the event of a civil uprising, the Philippine islands group, citron for Brazil, crimson for Canada, emerald for Ireland (a US landing in connection with 'Red'), garnet for New Zealand, gold for France and the French possessions in the Caribbean and South America, grey for the Azores and/or a Caribbean republic, green for Mexico war (either with Mexico or what was known as a 'Mexican Domestic Intervention' in order to defeat rebel forces and establish a pro-US government'), indigo for Iceland, lemon for Portugal, olive for Spain, orange for Japan, purple for Russia and the USSR and/or a central American republic (probably two separate plans), red for the UK, ruby for India, scarlet for Australia, silver for Italy, tan for Cuba, violet for China (intervention in internal matters), white for the USA (domestic opponent such as any communist attempt at a coup) and further developed as 'Garden Plot' to deal with civil disturbances and civil protests, and yellow for China (international conflict in general and more specifically the defence of Beijing (Peking) and relief of Shanghai during the 2^nd Sino-Japanese War). There were also combinations such as 'Red-Orange', which was necessitated by the Anglo-Japanese military alliance which expired and was not renewed in 1924.

Many of the war plans were extremely hypothetical, considering the state of international relations in the 1920s. Often, junior officers were given the task of updating the plans to keep them busy: this was especially true of 'Crimson'.

Some colours changed over time, and can result in confusion. Interestingly, although the USA had fought its most recent war against Germany and would fight another within a few years, intense domestic pressure emerged for the army to halt when it became known that the service was constructing a plan for a war with Germany, isolationists opposing any consideration of involvement in a future European war. This may have encouraged the army to focus on more speculative scenarios for planning exercises.

On the other hand, some of these plans were likely to be put into effect. For instance, Japan had used the opportunity afforded by World War I to establish itself as a major power and the USA’s primary strategic rival, especially in the Pacific Ocean. After the end of World War I most US officials and planners considered a war with Japan to be highly likely, though it was accorded a lower level of probability when Japan’s civilian government temporarily halted the programme of military expansion, which was resumed during 1931. 'Orange' (i) was the longest and most detailed of the plans, and many of its elements were carried over into 'Rainbow-5', current at the time of Japan’s December 1941 'Ai' attack on Pearl Harbor.

'Green' was also thought likely to be used. During the 1910s relations between Mexico and the USA were often volatile. In 1912, President William H. Taft considered sending an expeditionary force to protect foreign-owned property from damage during the Mexican Revolution. In 1916, US troops under General John Pershing invaded Mexico in search of Pancho Villa, whose rebel band had attacked Columbus, New Mexico. Earlier, US naval forces had bombarded and seized the port of Veracruz, and forced dictator Victoriano Huerta to resign. In 1917, British intelligence intercepted a telegram from the German foreign ministry to its embassy in Mexico City offering an alliance against the USA and assistance in the Mexican reconquest of the south-western portion of the USA. Released to US newspapers, this 'Zimmerman telegram' helped to turn US opinion against Germany and further poisoned the atmosphere between the USA and Mexico. Relations with Mexico remained tense into the 1920s and 1930s.

Between the end of the American Civil War in 1865 and the US entry into World War I during 1917, there were not-infrequent US military interventions in the affairs of Latin American countries, including Panama, Haiti, Cuba and Nicaragua. This policy continued during the 1920s and 1930s, and parts of the 'Gray' and 'Purple' plans were used although the relevant plans were not officially activated.