This is a pretty old tale and lots of people probably already know about it, but back in the 1920s and 1930s, the United States had a contingency plan for a conflict with Britain called War Plan Red. And, it seems, Japanwas the prime reason why the "special relationship" maybe wasn't quite so special after all at that time.
We all know how things turned out in the end, but for a while there, the Anglo-Japanese Alliance must have been having some funny effects in diplomatic circles in those times when Britannia did still rule the waves.
Apologies if this is boring and something most people already know about. I only (re?)-discovered it this morning and found the subject fascinating.