'Pastel I' was the US initial deception plan associated with 'Olympic' for feint amphibious landings in China, the Kurile islands group and parts of the Japanese home islands other than Kyushu (summer/autumn 1945).

Starting in May 1945 with a cover and deception appendix to a Commander-in-Chief Pacific Ocean Areas staff study for 'Olympic' and continuing with conferences at Admiral Chester W. Nimitz’s advance headquarters on Guam and at Manila, three US deception planners as well as several signals officers and senior planners of General Douglas MacArthur’s Commander-in-Chief Army Forces Pacific headquarters developed 'Pastel' (later 'Pastel I') as an outline deception plan for 'Olympic' together with a proposed transitional 'story' to 'Pastel' from from 'Bluebird', which was the cover plan for 'Iceberg' based on the 'story' of an invasion of Formosa and the south-east coast of mainland China, and on 14 June two men of the deception planning team left for Washington, DC, with the proposed scheme. The two men remained in Washington to a time well into July while the plan proceeded through the US high command staff system. It was a relatively slow process, and led to considerable irritation among the deception planners at the delay. It was not until 29 June, following meetings between the two deception planners and the Joint Security Control that the plan moved forward to the next stage, with the Joint Security Control’s recommended changes to render it compliant with the 'Broadaxe' overall plan for Pacific deceptions in 1945. After the usual staff committee consideration, the Joint Chiefs-of-Staff Committee approved 'Pastel' on 10 July.

Given the huge scale of 'Olympic', involving an initial assault by nine divisions, which was almost double the total of that involved in 'Neptune' (iii) for 'Overlord', 'Pastel' was the most elaborate of all US deception plans in terms of its basic nature and its anticipated execution. As approved by the Joint Chiefs-of-Staff Committee, the stated objective of 'Pastel' was to reduce the Japanese opposition to 'Olympic' by the greatest possible by persuading the Japanese to retain their very substantial land forces in China, dilute their air and naval efforts, reduce their vigilance in the proposed 'Olympic' assault area, reduce the size and rate of their reinforcement, and expend a significant proportion of their available effort on defences in areas other than the proposed assault area. Considerations appreciated as likely to affect the Japanese estimate of the situation included the need to preserve lines of communication on the continent of Asia; the attrition of Japanese forces; awareness that the US forces must perceive that even after an invasion the Japanese government might be transferred to the mainland to continue resistance; the need to retain significant forces in Manchukuo against the possibility that the USSR, which had recently terminated its non-aggression pact with Japan, might enter the war; and the obvious usefulness to the US forces of bases on the mainland. These bases could be used for the continued restriction of movement in the Yellow Sea and the Sea of Japan, the neutralisation of the defences of the home islands, and the destruction of Japanese industry; as bases for operations against mainland forces should the Japanese government flee there or if such forces should refuse to honour a capitulation by Tokyo; and to provide token forces should Soviets forces enter Manchukuo.

The capture of the Chusan and Shanghai areas, on the southern and northern sides of Hangzhou Bay, could allow the creation of such bases, additional airfields and naval anchorages, and also another route by which to supply the Chinese forces. Beaches were available in the areas, and the period between August and March would be suitable for amphibious operations.

Starting 30 days before X-Day, the day on which 'Olympic' was to be launched, it would probably become clear to the Japanese that there would be early landings in Japan, and it should become clear from X-10 that Kyushu was the target area for the initial landing on the home islands. Until X-10, therefore, the Japanese could not ignore the possibility that the initial landing might target Shikoku for its more central location in the home islands as well as its possession of suitable assault beaches, airfields and the sites for the rapid construction of other airfields: moreover, the period from November to February seemed to provide very favourable conditions for operations against it.

Accordingly, for maximum effect in persuading the Japanese to keep major forces in China, 'Pastel' should develop the threat of landing in the Chusan and Shanghai areas on about X-30. Then, at about X-55 the Imperial General Staff should be led to believe that the assault had been postponed but not abandoned, and also should be persuaded instead that there was a specific threat against Shikoku with a target date of X+55. With the real X-Day scheduled for 1 November, therefore, all this translated into the supposed threat of a landing in the area of Chusan and Shanghai on 1 October, and the Japanese should be convinced on about September 7 that this assault had been postponed and that an additional landing on Shikoku had been planned for a time late in December.

The first-phase 'story' in 'Pastel' was that the Joint Chiefs-of-Staff Committee had decided, given the heavy US losses and delays within the 'Iceberg' campaign on Okinawa, the need to release long-service veterans of the Pacific campaign and the logistic difficulties of redeployment of forces from Europe, that there should be no invasion of the Japanese home islands before the autumn of 1946. The 'story' was very carefully constructed to make it clear, largely at the behest of the US Navy, that the need for, or indeed the wisdom of, invading the Japanese home islands was still not a given. Meanwhile, on order to increase strategic bombarding, to speed the delivery of supplies to bolster Chinese strength, and to be ready for any possible evacuation of the Japanese government to the mainland and a Soviet entry into Manchukuo, the Joint Chief-of-Staff Committee had come to the decisions that air and naval bases should be developed in the Ryukyu islands group and that major lodgements should be taken in the areas of Chusan and Shanghai at about X-30 in preparation for a further advance into the region of the Yellow Sea. The land forces for this operation were to total 16 combat divisions and auxiliary troops. In addition, the 'story' added, the Joint Chiefs-of-Staff Committee had ordered the establishment of six divisions in the Aleutian islands group so that amphibious operations could be undertaken against the Kurile islands group late in 1945 as a preface to landings on the large northern island of Hokkaido during 1946.

Then, by X-55 or thereabouts, special means would have implemented the transitional 'story' from 'Bluebird' and 'Broadaxe' that the supposed worsening of the Japanese position in China, the rapidly improving capabilities of the Chinese forces, the unexpected speed of the redeployment of forces from Europe, and the success of the strategic bombing of Japan had led MacArthur and Nimitz to believe that the optimum employment of the originally earmarked for follow-up operations in China, after the Chusan and Shanghai landings, would be the diversion of about eight divisions for an amphibious landing on Shikoku on about X+55 for the development of air bases from which future operations could be supported, the effectiveness of the strategic bombing could be increased, and the blockade of Japan could be further enhanced.

The plan concluded with a general allocation of responsibility and the requirement that a major appendix be readied to set out specific responsibilities and timing.

The addition of the threat from the Aleutian islands group to Hokkaido, in the north of the home islands, reflected 'Broadaxe' and the renewed views of Lieutenant Commander Douglas Fairbanks Jr, the film star and one of the pioneers of US Navy deception, but the latter’s case that the Chusan and Shanghai area should be replaced by Shantung, and Shikoku by Hokkaido, was not accepted. A transitional 'story' for 'Bluebird', that on MacArthur s recommendation the Formosa operation had been indefinitely deferred, was the subject of discussion and agreement, but was through to be inappropriate for 'Pastel' proper.