At a length of 5,522 miles (8,891 kilometers), Canada and the United States share the longest non-militarized border in the world. Today we think of the two nations as the friendliest of neighbors, but at one time both nations had somewhat detailed plans for attacking one another… just in case.

The U.S. plan was titled “Joint Army and Navy Basic War Plan – Red,” and it included plans for the invasion of Canada by the United States as part of a larger worldwide military action. War Plan Red was actually designed for a war against England and it’s Commonwealth. The scenario imagined a conflict between England (code name Red) and the United States (Blue) fighting over vital international trade and commercial interests.

The plan was devised by the Pentagon U.S. military in 1934. In the event of such a military conflict, American planners assumed that England would use Canada (Crimson)⁠— a part of the British Commonwealth⁠— as a staging area for attacks on the United States. The Army had even researched which beaches the British might use for amphibious landings.

The American military wasn’t going to ignore a possible Anglo-Canadian threat, so a strategy for a preemptive takeover was devised. The ninety-four-page document outlined plans for stopping British reinforcements by taking the port of Halifax, then seizing the hydroelectric power plants at Niagara Falls while the Navy blockaded Canada’s Atlantic and Pacific ports. The Navy would also take control of the Great Lakes. Special notice was made about the Royal Canadian Mounted Police and how they were not a force to be taken lightly in a military action.

Next the U.S. Army was to attack in force on three fronts – advancing from North Dakota towards Winnipeg, moving from Vermont to capture Montreal and Quebec, and moving from the upper Midwest to take over the nickel mines of Ontario. The plan also called for a convoy to travel up Route 99 to Vancouver, and for the British colonies in the Caribbean to be taken. The goal of the U.S. was not only to defeat Canada, but to claim it as a prize, as described in the document:

“BLUE intentions are to hold in perpetuity all CRIMSON and RED territory gained. 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.”

All of the plans were discovered at the National Archives when they were declassified in 1974. The original War Plan Red was one of many “color plans” developed as academic exercises in a War Department with too little to do in the 1920s and 30s. The plans were an outgrowth of the creation of the new U.S. Army War College and the U.S. Army War Plans Division. With the development of a planning capacity the Pentagon figured they should get some practice.

As for the Canadians, they had their own plan outlining the invasion of the United States. Developed in 1921, it was called “Defense Scheme Number One,” and it called for Canadian soldiers to march on Albany, Minneapolis, Seattle and Great Falls, Montana. They were well aware that they lacked the military strength to defeat the U.S., so the thrust of the plan was to buy time for the British to arrive and help their commonwealth ally.

The department in Canada responsible for war planning had an annual budget of just $1,200. During the clandestine information-gathering for Defense Scheme Number One, staff members of the department actually entered the United States to take photographs and to procure free maps at gas stations.

Even though these war plans were just wildly imaginative speculation, there have been real invasions of Canada by Americans in the past. During the Revolutionary War, General Benedict Arnold led a failed attack on Canada, and during the War of 1812 U.S. troops attacked Canadians several times, but were driven back. In 1839, Americans and Canadians met in a deadly confrontation over a border dispute… it cost the life of one American cow and a Canadian pig.

In 1866, about eight hundred Irish-Americans in a group called the Fenian Brotherhood tried to make a statement for Irish independence by invading Canada to agitate the English. After crossing the Niagara River into Ontario they defeated a small group of Canadian militia. But when the British approached with a large force of troops, the Fenians mostly retreated back to the United States, where they were arrested. Some were captured by the Canadians and were eventually hanged.

Today some Canadians are still sensitive to talk of an American takeover. The two countries have at least four unresolved border disputes. In 2003 the Canadian Army set up an Internet chat room where citizens could discuss military issues. The Ottawa Citizen reported:

“One of the hottest topics on the site discusses whether the U.S. will invade Canada to seize its natural resources. Many individuals stated that if the such an attack did come, Canada could rely on a scorched-earth policy similar to what Russia did when invaded by Nazi Germany.”

Regardless, within years of the development of War Plan Red, Canada and the United States were allies in World War 2. Eventually both nations developed a common defense strategy for North America and both were charter signers in NATO. For Americans, Canada has secured it’s place in the “Axis of Congeniality,” and today the U.S./Canadian border has the largest number of legal crossings of any border in the world.

So you might wonder, is there an up-to-date 21st Century War Plan Red hidden away some obscure Defense Department office? When asked if such a plan existed today, a spokesman for the Pentagon said, “We don’t acknowledge which countries we have contingency plans for. We don’t acknowledge any of our contingency plans.”

That’s certainly not a denial. So, better not try any funny business, Canada. We might just have a plan.