Possible American Invasion Plans of Canada: War Plan Red and Beyond

The United States and Canada share what is often called "the world's longest undefended border," yet beneath this image of enduring friendship lies a surprising history of military planning. During the interwar period of the 20th century, both nations secretly developed comprehensive strategies to invade each other. The most notable American plan, known as War Plan Red, remains a fascinating study in strategic military planning and historical context. This report examines the development, details, and implications of American plans to invade Canada, especially War Plan Red, along with Canada's counterplan and the strategic thinking that informed these remarkable documents.

The period between the First and Second World Wars represented a significant shift in global power dynamics, particularly affecting relations between the United States, Great Britain, and Canada. Following World War I, the United States emerged as an increasingly dominant global force while Britain's imperial influence began to wane. Britain owed America approximately $22 billion after the war, signaling a fundamental shift in the economic balance of power between these nations9. This transition created uncertainty about future alliances and potential conflicts.

The British Navy had traditionally been structured to defeat the French, German, and American navies simultaneously, but this naval supremacy was increasingly challenged by the United States in the 1920s9. With Germany effectively neutralized as a naval power after WWI, Britain and the United States stood as the world's predominant naval forces4. This situation created strategic tensions despite the nations' ostensible alliance during the Great War.

In this atmosphere of shifting power dynamics and strategic uncertainty, military planners in both the United States and Canada began considering previously unthinkable scenarios. The British Deputy Chief of Naval Staff, Vice-Admiral Sir Osmond Brock, described the possibility of war between Britain and the United States as "very improbable" but notably stopped short of declaring it "impossible"4. It was against this backdrop that military planners began developing contingency strategies for potential conflicts between these historically allied nations.

Interestingly, Canada developed its invasion plan for the United States approximately a decade before the Americans created their strategy for invading Canada13. In April 1921, Lieutenant Colonel James "Buster" Sutherland Brown, who served as Canada's Director of Military Operations and Intelligence, drafted Defence Scheme No. 11. While Brown is sometimes portrayed as a rogue officer acting on his own initiative, he was actually following explicit orders from the Canadian chief of the general staff, who harbored concerns about potential American aggression9.

Defence Scheme No. 1 outlined a Canadian preemptive attack against the United States in the hypothetical case of America initiating hostilities against Canada or the British Empire1. The plan assumed that in the event of conflict, the United States would attempt to capture Montreal and Ottawa initially, followed by Hamilton, Toronto, the Prairie Provinces, and finally Vancouver and Southwestern British Columbia1.

The Canadian strategy called for immediate action upon receiving evidence of American invasion preparations. Flying columns stationed in western Canada would rapidly seize Seattle, Spokane, and Portland. Troops from Prairie Command would attack Fargo and Great Falls before advancing toward Minneapolis. Quebec-based forces would execute a surprise counterattack to capture Albany, while troops from the Maritime Provinces would invade Maine1. This aggressive first strike was not intended as a sustained offensive but rather as a delaying tactic.

After initial incursions, when American resistance intensified, Canadian forces would execute a strategic withdrawal to their own territory. During this retreat, they would systematically destroy bridges, railways, and other infrastructure to impede American pursuit1. The fundamental purpose of this plan was not territorial conquest but rather to buy precious time for Canada to mobilize its defenses and receive reinforcements from Britain.

Brown personally conducted reconnaissance for Defence Scheme No. 1, traveling in plainclothes throughout border regions of the United States from 1921 to 19261. His intelligence-gathering expeditions sometimes took on a somewhat comical character. In his notes from Vermont, Brown described local men as "fat and lazy but pleasant and congenial" and rural Vermont women as "a heavy and very comely lot"9. Historian Pierre Berton characterized these reconnaissance efforts as having "a zany flavour about it, reminiscent of the silent comedies of the day"1.

The United States developed its own plan for invading Canada approximately a decade after Defence Scheme No. 1. War Plan Red, also known as the Atlantic Strategic War Plan, was created following the 1927 Geneva Naval Conference and received approval in May 1930 from Secretary of War Patrick J. Hurley and Secretary of the Navy Charles Francis Adams III2. It was subsequently updated in 1934-352.

War Plan Red represented one component of a more extensive color-coded system of war planning developed by the United States Department of War during the interwar period of 1919-19392. Different potential adversaries were assigned specific colors: War Plan Green covered Mexico, Brown addressed the Philippines, Yellow targeted China, and Orange focused on Japan4. In this system, "Blue" designated the United States, while "Red" referred to the British Empire, with Canada specifically designated as "Crimson"2.

The plan provided a comprehensive assessment of Canada's geography, military resources, and transportation infrastructure before evaluating various pre-emptive strike options2. It did not identify Canada itself as a direct threat but rather as a proxy battlefield in a larger conflict with the British Empire5. The strategic rationale behind War Plan Red recognized that Canada's developed regions were particularly vulnerable due to their proximity to the U.S. border5.

War Plan Red's initial strategy envisioned incursions and short-term occupations of Canadian territory until the broader conflict with Britain reached resolution5. However, the 1935 update to the plan took a more ambitious stance, declaring that the United States would hold any gained Canadian territory "in perpetuity"5. This significant shift suggests an evolution in American strategic thinking regarding potential territorial annexation.

The plan specifically identified Maine as a strategic base for either cutting communications between Quebec/Montreal and the Maritime Provinces or launching strikes against Halifax and New Brunswick6. Control of Niagara power resources and coal supplies from western Canadian provinces was expected to result in "an immediate strangulation of its manufacturing and munitioning capacity"6.

Interestingly, War Plan Red considered it advantageous for the United States if Canada remained allied with Britain rather than declaring neutrality in any conflict. This would provide the U.S. with justification to "employ her greatly superior man-power in overrunning CRIMSON [Canada]"6. The plan identified economic and commercial expansion into previously British-controlled regions as the most likely catalyst for potential conflict between the United States and Great Britain6.

A particularly controversial aspect emerged with the plan's 1934 amendment, which reportedly authorized the use of poison gas against Canadians and included provisions for the strategic bombing of Halifax11. This escalation in proposed tactics reflects the evolving nature of warfare following the First World War and the increased willingness to employ chemical weapons despite their devastating effects during that conflict.

Both Defense Scheme No. 1 and War Plan Red devoted considerable attention to geographical factors that would influence military operations in North America. The Canadian Shield, a massive geological formation in eastern Canada, presented significant challenges for military movements11. Both plans recognized that Canada's vast size and largely uninhabited northern regions would limit most military activity to areas near the U.S.-Canada border.

The American planners produced detailed analyses of what they termed "critical areas" in Canada—regions of strategic importance whose control might materially influence the outcome of any conflict11. These assessments considered tactical, economic, and political factors in determining strategic significance. The Maritime Provinces, Quebec, Ontario, the Prairie Provinces, and British Columbia each received specific attention in these analyses11.

Canada's geographical vulnerability was clearly recognized in War Plan Red, which stated: "Geographically, while CRIMSON provides the RED Empire as a whole with advantageous bases at such widely separated points as to invite an initial dispersion of BLUE armed forces, CRIMSON itself occupies an extremely weak position with respect to BLUE. While its territory is of great extent, all well developed parts thereof lie close to the BLUE border; hence, they are especially vulnerable to attack from BLUE"5.

This assessment accurately identified a strategic reality that persists today: approximately 80% of Canada's population lives within 160 kilometers of the U.S. border7. This concentration of population and infrastructure near the border creates an inherent defensive vulnerability that would significantly influence any military conflict between the two nations.

War Plan Red remained classified until 1974, and Defence Scheme No. 1 similarly remained hidden from public scrutiny for decades2. Their declassification provided historians and military analysts with fascinating insights into interwar strategic thinking. While these plans might seem like historical curiosities, they continue to inform discussions about North American security cooperation and hypothetical conflict scenarios.

Modern military experts generally agree that an American invasion of Canada would likely succeed initially due to overwhelming American military superiority. However, holding conquered Canadian territory would present significant challenges7. The vast geography of Canada, particularly its remote northern regions, would make it extremely difficult to maintain supply lines and effective occupation forces. Winter conditions would further complicate military operations, especially in areas with minimal infrastructure7.

Perhaps more importantly, any American attempt to conquer Canada would likely face substantial resistance, both from Canadian forces and from within American society. The deeply integrated nature of U.S.-Canadian relations means that invasion plans would almost certainly leak, generating significant opposition within the United States itself7. The likelihood of American generals refusing to execute such invasion orders represents a substantial political obstacle to any modern equivalent of War Plan Red7.

A hypothetical modern invasion would also confront significantly different circumstances than those envisioned in the interwar period. Today, the United States and Canada are bound together through NATO, extensive trade relationships, and deeply integrated defense systems12. Recent historical evidence suggests that the United States has struggled with occupation and nation-building even in much smaller and less developed countries12. Given these factors, a successful long-term occupation of Canada seems highly improbable.

Interestingly, some echoes of these historical tensions emerged in early 2025 when U.S. President Donald Trump made controversial statements about Canada potentially becoming "the 51st state"3. While these comments primarily related to trade and economic policies rather than military action, they nonetheless sparked significant concern in Canada. The Canadian Prime Minister Justin Trudeau emphatically responded that there was "not a snowball's chance in hell" of Canada joining the United States3.

When questioned about potential military action against Canada, U.S. National Security Adviser Mike Waltz explicitly stated, "I don't think [President Trump] has any plans to invade Canada"8. Instead, Waltz characterized the administration's position as "a reassertion of American leadership in the Western Hemisphere"8. Despite these assurances, a brief trade war erupted on February 1, 2025, when the United States imposed substantial tariffs on Canadian and Mexican goods10.

These diplomatic tensions, while significant, operate in a completely different context than the interwar period when War Plan Red was developed. Modern interdependence between the United States and Canada creates powerful disincentives for military conflict that simply did not exist when military planners first contemplated these invasion scenarios.

The existence of War Plan Red and Defence Scheme No. 1 serves as a fascinating reminder that even the closest international relationships can experience periods of strategic uncertainty and contingency planning. These plans emerged during a unique historical moment when global power dynamics were shifting dramatically following the First World War. The rise of the United States and the relative decline of British imperial power created legitimate questions about future alignments and potential conflicts.

Both countries approached these contingency plans with professional thoroughness, conducting detailed analysis of geography, infrastructure, and military capabilities. The plans represent serious strategic thinking rather than merely hypothetical exercises, reflecting genuine concerns about national security in an uncertain international environment. Lieutenant Colonel Brown's extensive reconnaissance efforts and the detailed supplements to War Plan Red demonstrate the commitment of military planners to developing credible operational strategies.

Today, the idea of military conflict between the United States and Canada seems almost unthinkable. The two countries share the world's largest trading relationship, extensively integrated defense systems, and numerous formal alliance structures including NATO12. Contemporary tensions primarily manifest in trade disputes and diplomatic disagreements rather than military planning.

Nevertheless, these historical invasion plans provide valuable insights into strategic thinking, contingency planning, and the evolution of North American security arrangements. They remind us that international relationships, even seemingly permanent ones, remain subject to changing circumstances and strategic reassessment. The careful study of War Plan Red and Defence Scheme No. 1 offers important lessons about how military planners approach uncertain futures and prepare for even unlikely contingencies.

Citations:

1. https://en.wikipedia.org/wiki/Defence_Scheme_No._1
2. https://en.wikipedia.org/wiki/War_Plan_Red
3. https://en.wikipedia.org/wiki/Movements_for_the_annexation_of_Canada_to_the_United_States
4. https://www.historyextra.com/period/20th-century/war-plan-red-secret-invasion/
5. https://nationalpost.com/news/canada/war-plan-red-us-canada-britain
6. https://text-message.blogs.archives.gov/2019/02/05/u-s-and-canada-prepare-for-war-against-each-other/
7. https://www.reddit.com/r/imaginarymaps/comments/1cih4nz/plan_red_v2_the_american_invasion_of_canada/
8. https://www.aa.com.tr/en/americas/no-plans-to-invade-canada-says-trumps-national-security-adviser/3477482
9. https://macleans.ca/culture/books/how-canada-planned-to-invade-the-u-s-and-vice-versa/
10. https://en.wikipedia.org/wiki/2025_United_States_trade_war_with_Canada_and_Mexico
11. https://en.wikisource.org/wiki/War_Plan_Red/Supplement_No._3
12. https://macleans.ca/society/canada-51st-state-america/
13. https://themorningnews.org/article/war-plan-red
14. https://www.youtube.com/watch?v=kHC52FFJjfg
15. https://www.politico.com/magazine/story/2018/06/21/that-time-the-us-almost-went-to-war-with-canada-218881
16. https://www.dal.ca/news/2025/01/09/united-states-canada-state-51st.html
17. https://www.nytimes.com/2025/03/03/world/canada/trump-canada-tariff-economy-impact.html
18. https://www.nbcnews.com/politics/donald-trump/trump-national-security-adviser-no-plans-invade-canada-waltz-rcna191374
19. https://www.canada.ca/en/department-finance/news/2025/02/government-of-canada-announces-next-steps-in-its-response-plan-to-unjustified-us-tariffs.html
20. https://www.reddit.com/r/HistoricalWhatIf/comments/1du6c44/if_the_united_states_invaded_canada_how_would_it/