As it stands now, with unlimited railroad movement, land units are apparently the fastest things on earth... far outpacing jet fighters and missiles. It doesn't make sense, and its not fun when you land on someone's coast, only for them to dump *everything* they have on you on the next turn. I'm fine with being driven back into the sea, but not when they're using units from every single city from every facet of their empire, to do it. Currently, an invasion by sea is something you NEVER have to worry about once you get railroads, because you can just as easily have units anywhere you want. This in turn makes navies even more worthless than they are now.