Great thread.
War Plan Red
Was a plan for the United States to make war with Great Britain. It was developed by the United States Army during the mid 1920s, approved in May 1930 by the Secretary of War and the Secretary of Navy, updated in 1934–35, and officially withdrawn in 1939, following the outbreak of the Second World War.
The war was intended to be a continental war, waged primarily on North American territory between the United States and the British Empire. The assumption was that Canada would represent the primary theater of operations.