'Red' (i) was the US 'Color-coded War Plan' contingency scheme for war with the UK in the period between the world wars (May 1930/September 1939).

During the 1920s and 1930s, the US Joint Army and Navy Board developed a number of colour-coded war plans to outline potential US strategies for any or several possible (or rather hypothetical) war scenarios. The plans were developed by the Joint Planning Committee, which later became the Joint Chiefs-of-Staff Committee, and were officially withdrawn in 1939 in favour of five altogether more modern and therefore relevant 'Rainbow' plans developed to meet the threat of a two-ocean war against multiple opponents.

The use of a colour coding system for US war planning stemmed from the wishes of the US Army and US Navy to use the same symbols in their plans. At the end of 1904, the Joint Army and Navy Board adopted a system of colours, symbols and abbreviated names to represent countries, and many war plans became known by the colour of the country to which they were relevant. This was a convention which survived to the end of World War II. As the convention of using colours became accepted, some colours were eventually reused: 'War Plan Gray', for instance, originally referred to Italy but eventually became a plan for the capture and/or occupation of the Azores island group.

In all the plans, it should be noted, the USA was always 'Blue'.

The plan which was the subject of the greatest work and subsequent development was 'War Plan Orange', a series of contingency plans for a war with Japan alone: this plan was outlined in 1919 and officially adopted in 1924. 'War Plan Orange' was the basis, in part at least, for the war actually waged against Japan in World War II, and included a vast economic blockade from mainland China and the plans for interning the Japanese-American population of the Hawaiian islands group.

'War Plan Red' was a plan for war against the UK and Canada, while the plans for operations in different British territories had war plans of different shades of red: the UK was 'Red', Canada 'Crimson', India 'Ruby', Australia 'Scarlet', New Zealand 'Garnet' and all other parts of the British empire 'Pink', though Ireland, at the time a free state within the British empire, was 'Emerald'. The plan was kept updated as late as the 1930s.

'Red' outlined a theoretical war between the USA (the 'Blue' forces) and the British empire (the 'Red' forces). The plan was developed by the US Army during the mid-1920s, and was officially withdrawn in 1939, when it and others like it were replaced by the five 'Rainbow' plans created to deal with the Axis threat.

The 'Red' war was envisaged as a continental war, waged primarily on North American territory between the USA and Canada, on the assumption that Canada was an ideal geographic base for a British war against the USA. There is some debate over whether the plan was actually meant to be put into action. Although an Anglo-US war had been a possibility during the late 19^th century, the likelihood of this declined substantially following the turn of the century. The amicable negotiations of the tense Venezuelan/British Guianan border dispute, the Henceforward Treaty, the establishment of the International Joint Commission, and the Washington Naval Treaty are examples of the increasingly close US-Canadian relationship during this period.

'War Plan Red' is generally characterised as lacking in detail, indicating its low priority in the planners' eyes. 'War Plan Red' was only one of a number of US colour-coded war plans developed at this time. Many of these addressed highly speculative scenarios, since heavily focusing plans on specific countries like Germany would have appeared militaristic and aroused domestic opposition. 'War Plan Red' was declassified in 1974, and caused a stir in US-Canadian relations for Canada, designated 'Crimson' in the plans, was to have been the principal target of the US forces. This war plan did not go into detail regarding offensive or defensive naval campaigns against the UK, at that time still the world’s dominant naval power.

'War Plan Red' was posited on the outbreak of a war between the USA on the one hand and the UK and its commonwealth and empire on the other, and outlined the steps necessary to defend the USA’s eastern seaboard on the Atlantic Ocean against a British attempt to invade the US mainland. It should be noted that 'War Plan Red' did not create any operational details, and lacked both presidential and congressional approval. Only the Congress can declare war, and in this period of US history it made no war plans.

'War Plan Red' was developed by the US Army after the 1927 Geneva Naval Conference, and after being approved in May 1930 by the Secretary of War and the Secretary of Navy, was updated in 1934/35. On the outbreak of World War II in 1939, it was decided that no further planning was required, but that the plan be retained.

The war plan outlined the actions which would have to occur to trigger a state of war between the UK and the USA, and suggested that the British would initially have the upper hand by virtue of the strength of the Royal Navy. The plan further assumed that the UK would probably use its dominion in Canada as a springboard from which to initiate a retaliatory invasion of the USA. The assumption was that the UK would initially fight a defensive battle against invading US forces, but that the USA would eventually defeat the UK by blockading the British Isles and cutting British food supplies.

'War Plan Red' first described Canada’s geography, military resources and transport systems, and went on to evaluate a series of possible US pre-emptive campaigns to invade Canada in several areas and occupy key ports and railways before British troops could provide reinforcements across the Atlantic Ocean. The assumption was that the UK would use Canada as a staging point for an invasion of the USA, and it was posited that US attacks on Canada would prevent the UK from making use of Canadian resources, ports and air bases.

An essential initial US move was a joint army and navy attack to capture the port city of Halifax, Nova Scotia, thereby effectively separating Canada from the possibility of British seaborne reinforcement. The next US objective was to 'seize Canadian Power Plants near Niagara Falls' and then a full-scale invasion on three fronts: from Vermont to take Montreal and Quebec, from North Dakota to take the railhead at Winnipeg, and from the US mid-west to capture the strategic nickel mines of Ontario. In parallel, the US Navy was to seize the Great Lakes and blockade Canada’s Atlantic and Pacific ports.

The primary zones considered in 'War Plan Red' were the eastern maritime provinces (Nova Scotia, New Brunswick and Prince Edward Island); Quebec and the St Lawrence river valley; Ontario and the Great Lakes; Winnipeg; and Vancouver and Victoria.

In the maritime provinces Halifax was to be seized, after a first strike using poison gas, in order to deny the British a major naval base and cut maritime links between Britain and Canada. The plan considered several land and sea options for the attack, and concluded that a landing in St Margarets Bay, a undeveloped area near Halifax, would be superior to a direct assault via the longer overland route. Failing to take Halifax, the USA could occupy New Brunswick by land to cut off Nova Scotia from the rest of Canada at the key railway junction at Moncton.

In Quebec and the St Lawrence river valley, the primary objective was to be the seizure of the cities of Montreal and Quebec, which would isolate the remainder of Canada from the eastern seaboard, preventing the movement of soldiers and resources in each direction. The routes from northern New York to Montreal and from Vermont to Quebec were both deemed suitable for offensive action, and Quebec was the more critical primary target.

In the Ontario and the Great Lakes area, a US occupation would gain control of Toronto and most of Canada’s industry, while also preventing the UK and Canada from using the area for air or land attacks against the US industrial heartland in the mid-west. The plan therefore proposed simultaneous offensives from Buffalo across the Niagara river, from Detroit into Windsor, and from Sault Ste Marie into Sudbury. Controlling the Great Lakes for US transport was seen as logistically necessary for a continued invasion.

In the Winnipeg area, Winnipeg itself was a central nexus of the Canadian railway system for connecting the entire country. The plan foresaw no major obstacles to an offensive from Grand Forks, North Dakota, to Winnipeg.

In the Vancouver and Victoria area, Vancouver was of secondary importance as it was very far removed from the UK, but nevertheless its occupation would deny the British a naval base and sever Canada from the Pacific Ocean. Vancouver could readily be attacked overland from Bellingham, Washington, while Vancouver island could be attacked by sea from Port Angeles, Washington. The port of Prince Rupert in British Columbia had a rail connection to the rest of Canada, but a naval blockade was seen as simple once Vancouver had been taken.

Unlike the later 'Rainbow-5' plan, 'War Plan Red' envisaged no offensive action outside the western hemisphere. The plan assumed that the British would have a much larger army and slightly larger navy. Because of the the British empire’s historical strength, the USA had traditionally planned for a defensive war with the the UK, and 'War Plan Red' recommended the retention of this strategy even as the US military grew in size to match that of the UK. The plan’s authors saw the conquest of Canada as the best way to strike at the British empire, and believed that a successful conquest would prompt the UK to negotiate for peace. One of the plan’s flaws, however, was that it did not discuss how to attack the British empire in the event that Canada declared itself to be neutral, and this was a factor which the plan’s authors believed probable. However, the plan advised against any US acceptance of such a declaration without permission to occupy Canadian ports and some territory until the end of the war.

On the basis of large-scale war gaming undertaken at the Naval War College, the plan rejected the concept of attacking British shipping or attempting to destroy the British fleet. The main US naval strength would instead stay in the western part of the North Atlantic to block maritime traffic between Canada and the UK, await for a good opportunity to engage the British fleet on advantageous terms and, if successful, this would then open the way for the USA to attack British trade and colonies in the western hemisphere.

In 1935 'War Plan Red' was updated, and specified the routes to be employed in the invasion. It was also suggested that the USA should construct three military airfields, disguised as civilian airports, near the Canadian border, and for this task apparently secured a Congressional appropriation of US$57 million to build three border air bases for the purposes. The military nature of these airfields was 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 1 May 1935.

The plan envisaged that no captured British territory would be returned after the war, but instead that these provinces and territories would become US states and territories.

The Royal Navy prepared no formal plan for war with the USA during the first half of the 20^th century. The government of David Lloyd George in 1919 restricted the navy from doing so specifically to prevent it from using US naval expansion to justify the construction of more warships. Like their counterparts in the USA, the majority of Royal Navy officers believed that co-operation with the other nation, on the basis of a shared language, culture and basic democratic ideology, was the best way to maintain world peace. However, the British did fear that attempts to regulate trade during a war with another nation might force a war with the USA as, for instance, it had in 1812.

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 USA, and therefore did not plan to do so, as the loss of Canada would not be fatal to the UK. Moreover, an invasion of the USA was wholly unrealistic, and a naval blockade was too slow. The navy could not use a defensive strategy of waiting for the US fleet to cross the Atlantic because British trade was too vulnerable. Royal Navy officers believed that the UK was so vulnerable to a blockade that, in the event that a superior US fleet appeared off the British Isles, the UK would quickly surrender. The officers planned, instead, to launch attacks on the US fleet from a western hemisphere base such as Bermuda, while other warships based in Canada and the West Indies harried US shipping and protected British trade. The navy would also bombard coastal bases and make small amphibious assaults. India and Australia would co-operate in the capture of Manila in the Philippine islands group, to prevent attacks by US warships based there on British trade in Asia and perhaps a conquest of Hong Kong. The British officers hoped that such acts would result in a stalemate, which would make continued war unpopular in the USA and pave the way to a negotiated peace.

It is worth noting that a Canadian officer, Lieutenant Colonel James Sutherland Brown, developed an earlier Canadian counterpart to 'War Plan Red' as the Defence Scheme No. 1 on 12 April 1921. Maintaining that the best defence was a good offence, 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 US troops to the flanks and thus away from an assault on Canada in a process which would buy the time for empire allies to deliver reinforcements. Defence Scheme No. 1 was terminated by the chief of the Canadian general staff, Major General Andrew G. L. McNaughton in 1929, one year before the approval of 'War Plan Red'.