I have read that in 1939, the Us Navie’s war plans included a study for a proposed attack upon the British Royal navy. Is this true? Why was such a conflict anticipated? And, in the US Navy’s assessment) would the US have been victorious in such a war?
War really wasn’t “anticipated”. But it did give those staffers sumthin to do…
Staff report
http://www.straightdope.com/mailbag/mcanadawar.html
military planners have to provide for a wide range of contingencies. Some, like war with Iran, are highly possible and receive a good deal of effort. Others are deemed less likely, and some are very unlikely but are done (somewhat perfunctorily) anyway.
I would expect that the military has plans to invade or attack every country in the world, and various combinations. It’s good practice, and when the president comes to you and says, “We have to invade Uruguay immediately,” you don’t end up saying, “Well, we need time to make up a plan.”
I’d love to see Liechtenstein’s plans to invade Greenland 
[ol]
[li]Steal underwear[/li][li]???[/li][li]Profit[/li][/ol]
Well there was the wiki article quoted , but since you mentioned 1939 I would have to guess that Britain would have fallen to Germany and that the US would have wanted to keep the British naval units in home waters , from becoming part of the extended kriegsmarine.
Since the USA was not at war with anyone in 1939/40 this is kinda moot. Before commenting about an American naval victory over vichy (mosely) naval assets , I would probably look up any plans for a royal naval evacuation to Allied and Colonial nations.
But I think it would probably look like the destruction of French Naval assets in North Africa.
Declan
There’s also the possibility that country X will be invaded by some other nation and that you’ll be called upon (or take it upon yourselves) to intervene. Much of the same information will be useful in either case - whether it’s an attack against the native government of country X, or an invasion against hostile occupying forces.