We also had a plan for war with England (before D-Day).
The military routinely have contingency plans for every possibility you can thunk of and a few thousand you can’t.
SOP
There is no doubt in my mind that our armed forces can defeat anyone else out there if there was a conventional war.
What would impress me far more than having twelve different plans to defeat the British and any combination of their colonies (yes, I am sure we still have them today) would be a plan to effectively defeat modern threats like terrorists and insurgencies. One that actually works, unlike our counterinsurgency strategy from ten years or so ago that was so complicated that only an academic could think it would work.