The plans of the US and British navies for an Anglo-American war have received little attention because most historians accept the premise that such an event was 'unthinkable'; that the likelihood of war between the United States and the British Empire was so remote as to have become an absurdity. For planners in the armed services, however, who accept as a matter of course that states use force whenever necessary to further their interests, it was natural to assume that any other state would, in certain circumstances, resort to war. Also, while it is true that British and US statesmen did not rate highly the likelihood of war between their two countries, in moments of crisis their thoughts did turn to the possibility. No less a figure than Winston Churchill himself, the architect of the Anglo-American 'special relationship' and, after 1963, an honorary American citizen, could write in 1927 that although it was 'quite right in the interests of peace to go on talking about war with the United States being "unthinkable", everyone knows that this is not true.'
The consequences of the outbreak of war were potentially so great that no responsible decision-maker could afford to dismiss the likelihood out of hand. Americans feared that war with the British Empire might lead to the destruction of the US fleet and the temporary interruption of US overseas trade; to attacks on major industrial centres by British air forces based in Canada; and to the invasion of the continental United States by an imperial army drawn from Britain, Canada, and the other British colonies. For Britain, the results would be just as damaging and much more probable: the destruction of the British fleet, the conquest of British colonies and former colonies in the western hemisphere, the disruption of Britain's overseas trade, and, in the event of defeat, an immense blow to British prestige. Although each of the two assumed that it would never start the war, each also knew that it could not predict the other's conduct with certainty. Historians, however, frequently treat the attempts of British and American military planners to grapple with the problem of an Anglo-American war as a historical curiosity, the product of over-active imaginations with too much time on their hands. Therefore, although the US navy's plans for war against the British Empire have been examined in some detail, they are usually treated as little more than a useful exercise. Indeed, it has been suggested that the 'essential value' of the US naval war plan against Britain -'Plan Red' was to accustom service planners to dealing with the complexities of an Atlantic centred conflict. There is some truth to this view, but it is not the whole truth. From the historian's perspective, Plan Red is of less interest as a stage in the evolution of the later Rainbow plans (5 contingencies for war on multiple fronts) prepared between 1939 and 1941 by the US Joint Planning Committee, than as a window into the strategic mind of the US navy. The same is true of British plans for a naval war with the United States. The British plans have not received the same attention as their US counterparts, for the simple reason that no formal plans were ever committed to paper.
An appreciation of the psychology behind this decision making does, however shed some interesting and useful light on a number of contemporary attitudes. It highlights the competitive, often antagonistic side of Anglo-American relations during the 1920s and the level of mutual mistrust that existed: it is too often forgotten that naval rivalry, war debts, and arguments over belligerent versus neutral rights placed considerable strain on Anglo-American friendship during this period. It also illuminates the perceptions each had of the other's power, most notably the high regard of the US armed forces for Britain. It perhaps, also reveals both navies' assumptions about the efficacy and application of sea power.