War Plan Red Joint Army and Navy Basic War Plan Red was a war plan created by the United States Army and Navy in the late 1920s and early 1930s to estimate the requirements for a hypothetical war with Great Britain ( the " Red " forces ) . " War Plan Red discussed the potential for fighting a war with Britain and its Empire and outlined those steps necessary to defend the Atlantic coast against any attempted mainland invasion of the United States . It further discussed fighting a two - front war with both Japan and Britain simultaneously ( as envisioned in War Plan Red - Orange ) . War Plan Red was not operationalized and did not have presidential or Congressional approval . In the U . S . only the Congress can declare war , and it made no war plans . President Herbert Hoover was known as a pacifist . War Plan Red was developed by the United States Army following the 1927 Geneva Naval Conference and approved in May 1930 by the Secretary of War and the Secretary of Navy and updated in 1934 – 35 . In 1939 on the outbreak of World War II and Britain ' s war against Nazi Germany , a decision was taken that no further planning was required but that the plan be retained . War Plan Red was not declassified until 1974 . The war plan outlined those actions that would be necessary to initiate war between Britain and the United States . The plan suggested that the British would initially have the upper hand by virtue of the strength of the Royal Navy . The plan further assumed that Britain would probably use its Dominion in Canada as a springboard from which to initiate a retaliatory invasion of the United States . The assumption was taken that at first Britain would fight a defensive battle against invading American forces , but that the US would eventually defeat the British by blockading the United Kingdom and economically isolating it . History . War Plan Red was one of a number of U . S . color - coded war plans developed by the U . S . after the First World War . When War Plan Red was declassified in 1974 , it caused a stir in American - Canadian relations because Canada , codenamed " Crimson " in the plan , was to have been the principal target of American forces . Outline . War Plan Red first set out a description of Canada ' s geography , military resources , and transportation , and went on to evaluate a series of possible pre - emptive American campaigns to invade Canada in several areas and occupy key ports and railways before British troops could provide reinforcement to the Canadians - the assumption being that Britain would use Canada as a staging point . The idea was that the American attacks on Canada would prevent Britain from using Canadian resources , ports , or airbases . A key move was a joint US army - navy attack to capture the port city of Halifax , cutting off the Canadians from their British allies . Their next objective was to " seize Canadian Power Plants near Niagara Falls " This was to be followed by a full - scale invasion on three fronts : From Vermont to take Montreal and Quebec , from North Dakota to take over the railhead at Winnipeg , and from the Midwest to capture the strategic nickel mines of Ontario . In parallel , the U . S . Navy was to seize the Great Lakes and blockade Canada ’ s Atlantic and Pacific ports . Zones of operation . The main zones of operation discussed in the plan are : No attacks outside Western Hemisphere . Unlike the Rainbow Five plan , War Plan Red did not envision striking outside the Western Hemisphere . The plan assumed that the British Empire would have a much larger army and slightly larger navy . Because of the Empire ' s historical strength , the United States had traditionally planned for a defensive war with the British . War Plan Red recommended continued use of this strategy even as American military might grow to match Britain ' s . Its authors saw conquering Canada as the best way to attack the British Empire and believed that doing so would cause Britain to negotiate for peace . A problem with the plan was that it did not discuss how to attack the Empire if Canada declared its neutrality , which the authors believed was likely . ( The plan advised against accepting such a declaration without permission to occupy Canadian ports and some land until the war ended . ) Based on extensive war games conducted at the Naval War College , the plan rejected attacking British shipping or attempting to destroy the British fleet . The main American fleet would instead stay in the western North Atlantic to block British - Canadian traffic . The navy would wait for a good opportunity to engage the British fleet , and if successful would then attack British trade and colonies in the Western Hemisphere . In 1935 War Plan Red was updated and specified which roads to use in the invasion . " The best practicable route to Vancouver is via 99 " ( Carlson , 2005 ) . Further , in 1935 Americans planned to build three military airfields near the Canadian border and disguise them as civilian airports . " In February 1935 , the War Department arranged a Congressional appropriation of $ 57 million to build three border air bases for the purposes of pre - emptive surprise attacks on Canadian air fields " ( Berlin Glasnost , 1992 – 2007 ) . The airfields were to be kept secret , but their existence was accidentally published by the Government Printing Office and reported on the front page of the " New York Times " on May 1 , 1935 . American war planners had no thoughts of returning captured British territory . " The policy will be to prepare the provinces and territories of CRIMSON and RED to become states and territories of the BLUE union upon the declaration of peace . " British strategy for war against the United States . The Royal Navy never prepared a formal plan for war with the United States during the first half of the 20th century . The government of David Lloyd George in 1919 restricted the navy from doing so to prevent it from using American naval growth to justify building more ships . Like their American counterparts , most Royal Navy officers viewed cooperation with the other nation as the best way to maintain world peace due to the shared culture , language , and goals , although Britons feared that British attempts to regulate trade during a war with another nation might force a war with the United States . Royal Navy officers generally believed that if war did occur , they could transport an army to Canada if asked , but nonetheless saw it as impossible to defend against the much larger United States , so did not plan to do so , as Canada ' s loss would not be fatal to Britain . An invasion of the United States was unrealistic and a naval blockade was too slow . The navy could not use a defensive strategy of waiting for the American fleet to cross the Atlantic because Imperial trade was too vulnerable . The Royal Navy officers believed that the United Kingdom was so vulnerable to a blockade that , if a superior American fleet appeared near the British Isles , Britain would quickly surrender . The officers planned to , instead , attack the American fleet from a Western Hemisphere base , likely Bermuda , while other ships based in Canada and the West Indies would attack American shipping and protect Imperial trade . The navy would also bombard coastal bases and make small amphibious assaults . India and Australia would help capture Manila to prevent American attacks on British trade in Asia and perhaps a conquest of Hong Kong . The officers hoped that such acts would result in a stalemate making continued war unpopular in the United States , followed by a negotiated peace . Canadian counterpart . Canadian military officer Lieutenant Colonel James " Buster " Sutherland Brown developed an earlier counterpart to War Plan Red called Defense Scheme No . 1 on April 12 , 1921 . Maintaining that the best defense was a good offense , " Buster " Brown planned for rapid deployment of flying columns to occupy Seattle , Great Falls , Minneapolis , and Albany . With no hope of holding these objectives , the idea was to divert American troops to the flanks and away from Canada , hopefully long enough for Imperial allies to arrive with reinforcements . Defence Scheme No . 1 was terminated by Chief of the General Staff Andrew McNaughton in 1928 , two years prior to the approval of War Plan Red .