By pure chance, I found out there was a Plan red for the event of war between the states and Britain. The plan was conceived in the late 20s and early 30s of the previous century. It seems the article makes no mention of the expected reasons for such a war.

Initially I assumed it was customary to plan for the event of war with any serious rival - particularly since there were a series of Colour Plans for various war theatres. But the plan was classified until 1974, which seems to indicate it was not expected there would be such a plan.

So, did the United States expect war against Britain and why?

Wikipedia further states the following, which I don't know how to assess, but which seems important:

War Plan Red was developed by the United States Army following the 1927 Geneva Naval Conference and approved in May 1930 by Secretary of War Patrick J. Hurley and Secretary of Navy Charles Francis Adams III and updated in 1934–35; it was not presented for presidential or Congressional approval. Only the United States Congress has the power to declare war.

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    I can't claim any specialist knowledge, but I'd have been surprised if the United States didn't have contingency plans for war against the Great Powers of the 1920s (which included the UK), or other smaller states that might threaten its sphere of influence. That's what strategic military planning is supposed to be about. I would also not be surprised to discover that similar plans exist today. Jun 3, 2017 at 12:13
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    "I assumed it was customary to plan for the event of war with any serious rival". I'd assume that too. Since Britain, with it's large Navy (and Canadian bases), was theoretically the 'greatest' danger to the USA, it would make sense to have plans just in case. Jun 3, 2017 at 12:19
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    And, in any case, it would be very useful to assess current capabilities. In a war with the UK the major factor would have been the fleet, and if that was revealed to be inadequated, getting it up to an acceptable level could have taken more than a decade; comparatively raising an army is relatively easy (the USA did that in a year at the beginning of WWI). So, checking "can we beat them" made sense even if political relations were friendly, because if the answer was no and the UK were to become an enemy, the USA would have a significant disavantage for quite a time.
    – SJuan76
    Jun 3, 2017 at 12:39
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    Also take into acount that if we talk about "Britain" in 1920 we mean "British Empire", with its colonies/puppets in India, Egypt (Suez Channel), the Caribbean, and the Commonwealth. That meant a lot more of possible points of conflict with the USA than "Britain" proper.
    – SJuan76
    Jun 3, 2017 at 12:42
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    In hindsight it can look like the alliances of the first half of the 20th century were "obvious", but that wasn't the case in real time. As late as 1905, Britain considered a future war with France just as likely as a future war with Germany. The US had a long history of conflicts and disputes with the UK (the War of 1812, the Oregon dispute in the 1840's, concerns over possible UK support of the Confederacy in the 1860's, the race for Hawaii, etc.).
    – tbrookside
    May 6, 2019 at 14:08

4 Answers 4


There are many reasons for making such plans. They include:

  • Keeping a planning staff active and in practice.
  • Discovering what forces would be required for different kinds of war, so that the forces created in peacetime are as widely applicable as possible, and you know how to expand them.
  • Actual political potential for a war.

It was conceivable that the fairly friendly relations between the US and UK that had existed during the early twentieth century and WWI could have broken down in the negotiations in 1921-22 over the Washington Naval Treaty. This did not happen.

Studying a conflict with the UK would have been a good example of how to fight a naval war against a powerful opponent, which also has a land border with the USA, via Canada. So it was a good exercise for the planners.

There doesn't seem to have been any realistic expectation of war. Relations during the inter-war years were pretty good, but not perfect. The UK abandoned its alliance with Japan in December 1921 in favour of good relations with the US, although the alliance did not formally end until 1923.

The reason that the plan stayed classified for so long can be attributed to the "paranoid tabloid" school of British politics. There are several British newspapers, currently most notably the Daily Mail and Daily Express, whose appeal seems to be based on sensational and frightening stories. I have no doubt that in 1974 they made a great fuss along the lines of "American Plans To Attack Us!"

The fact that there were outline plans for wars against all the great powers of the period would make no difference to them. Reasonableness and insight are not what they are selling. In the UK, TV has obligations about fairness and balance, but newspapers do not.

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    Actually, there used to be a "fairness doctrine" in American broadcasting but it was dropped in 2011. Freedom of the press is nearly absolute in America - even our libel laws are very limited compared to the UK. If there is any thought given to "fairness and balance" in US media, it does not come from any legal obligation.
    – pokep
    Jun 3, 2017 at 16:28
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    John Dallman - I have no doubt that in 1974 they made a great fuss along the lines of "American Plans To Attack Us!" I would guess their headlines might be more punning. More like "US Plans to Attack Us!" Ha ha.
    – MAGolding
    Jun 3, 2017 at 21:32

Britain was formally allied with Japan. And a war with Japan could theoretically lead to war with Britain. This could happen, for instance, with regard to U.S interests in Asia, particularly China. The U.S. supported an Open Door Policy in that country, the other two did not.

America had gone to war with Britain in 1812, and "come close" several more times in the 19th century.

But it was mostly a "wargaming" exercise to test the 5-5-3 ratio naval tonnage ratio for the U.S., U.K., and Japan, and the impact of the U.S.'s 5 versus the other two's 8.

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    I regret I cannot instantly find any sources or explanations so offer this as comment rather than answer, but I am sure I read that there were people in Britain in the 1920s worried about a future war with the USA, causing Winston Churchill (whose parentage was Anglo-American) to comment that while no sensible person would want it the possibility of war between the USA and British Empire, the 2 biggest naval powers, could not be excluded. I have also read that in the 1920s the British Royal Air Force had plans for possible war with France, as (at that time) the main European military power.
    – Timothy
    Jun 4, 2017 at 13:28
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    China obviously...
    – kubanczyk
    Jun 4, 2017 at 21:58
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    @Timothy:England and France hadn't been allies for that long, and with Germany (temporarily) out of the balance of power equation, war between the other two was plausible; even Hitler noted that in Mein Kampf. And England's balance power calculation had always consisted of keeping its fleet at least as large as that of the next two powers combined; an axiom that was violated by the Washington Conference.
    – Tom Au
    Jun 6, 2017 at 9:58

The US Navy developed plans for a naval war with Great Britain for several reasons:

  1. The US had been to war with GB on multiple occasions.
  2. The Royal Navy was the largest navy in the world.
  3. If the US Navy was built to defeat or significantly damage the Royal Navy they could take it as a given that they could take on any navy in the world on, at worst, equal terms.
  4. The US Navy also had to be able to counter the growing threat posed by the Imperial Japanese Navy, and thus needed to be large enough to fight a "two-ocean" war simultaneously.

Thus the US Navy was not just concerned with a battle in the Atlantic vs. the Royal Navy - it also was concerned that it would have to fight a simultaneous battle in the Pacific against the IJN.

It was not until the Great Depression that this doctrine changed. Prior to his service as Chief of Naval Operations (CNO) Admiral William Veazie Pratt served as part of the US delegation to the London Naval Conference, where he became personally familiar with the men in charge of the Royal Navy from both a military and civilian perspective. When he became CNO in September of 1930 Admiral Pratt recognized that although the Royal Navy was the largest fleet in the world the political realities had changed. America and Great Britain had become long-standing and close allies, and Great Britain and the Royal Navy thus no longer posed a threat to the United States. As such, priorities were shifted. The assumption was made that the Royal Navy would take principle responsibility for fighting in the Atlantic and the Mediterranean, while the US would take principle responsibility for fighting in the Pacific, and that the US Navy could thus be sized appropriately for a "one ocean" war.

I served briefly aboard USS William V. Pratt (DDG-44) as a 1st-class midshipman during the summer of 1978, and so became acquainted with Admiral Pratt's contributions to the US Navy.

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    I commend you for digging into this old question. Main good point here I think is that its the military's job to have war plans ready to go for pretty much any conceivable scenario. This is no different than how the NY Times has obituaries ready to go for any celebrity, even healthy ones. No doubt the UK Navy has a plan for dealing with the US as well. A generic plan for dealing with a small Latin American coastal nation might do for several countries, but clearly the UK is in a class of its own and thus merits its own unique plan.
    – T.E.D.
    Mar 6, 2018 at 14:17

This paper goes into detail about the war plans of both the British and the Americans. It's quite readable, and if you're interested, I'd suggest taking a look.

For the question itself: interpreting your question as if the US and UK are friends, why bother planning for a war against a friend?, then you'd be right, most of the time both sides thought it was unlikely to go to war with each other, but they thought about it anyway in times of crises. After all, even if you know for sure that you will not resort to force, can you say the same of your erstwhile ally?

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. And 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 turned to the possibility. No less a figure than Winston Churchill, 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.'

A second reason is that, no matter how unlikely, if there were a war, the consequences would be dramatic. Think about why people buy insurance for example - sure it's unlikely that your house burns down, but if it does, can you afford to be uninsured?

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.

Finally, war planners keep "in shape" by planning for war. They are more familiar with what assets they have, what (natural) obstacles they might have to deal with, how long it takes to deploy ships from the Pacific to the Atlantic, and so on:

Indeed, it has been suggested that the 'essential value' of the US naval war plan against Britain - Plan Red 3 - 'was to accustom service planners to dealing with the complexities of an Atlantic centered conflict'

You'll find more examples later in the document. For example, British war planners thought about the threat of the US moving a fleet from the Atlantic to the Pacific, via the Panama Canal. This is not just dangerous to British trade, it might have led to the capture of some colonies such as Hong Kong. As a result, British planners thought about capturing the Philippines to deprive the American navy of bases. Either way such a war is going to be complex, and of course, when it's complex, it's necessary to think about it.

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