Well, the codebook used to break Enigma was captured by a British submarine, and IIRC the work done to break it was all done at Bletchley Park (hence why I actually remember the name; it's kinda famous now round here).
I'm sure there could have been Americans involved on the team (though I believe it was mostly European personnel) but to present it as a solely American effort would be just as wrong as claiming D-Day was a solely British effort - completely incorrect.
Yes, Hollywood does interpret (and plain rewrite...) the facts just to sell more movies, but that doesn't make it ok...