6. MacArthur wanted the invasion to be an all American operation
Douglas MacArthur has been accused many times of having an enormous ego which sometimes overrode his judgment, but in the case of Operation Downfall, his arguments for the invading troops to be all Americans were sound. They were based on logistics. In an operation so large (Downfall would have been the largest seaborne invasion in history) logistical problems, particularly resupplying the troops engaged in battle with ammunition and other supplies, were inevitable. The British and Australian troops used different weapons, of different calibers than the Americans. This included rifles, sidearms, machine guns, tanks, artillery, and virtually everything else.
American planners depended on reinforcing and resupplying Olympic with units from Coronet if necessary, themselves redeployed from other Pacific theaters of operation. Nonetheless, in the early summer of 1945, Commonwealth forces were committed to participation in Operation Coronet, though MacArthur insisted that they be equipped with American weapons. MacArthur also demanded that units of the Indian Army not be included, to which the planners acquiesced. MacArthur’s argument against the use of Indian troops was based on the difference in language, which he believed could cause communication issues detrimental to his overall command of the ground forces.