To your question, there are none currently active with the Navy.

The USS New Jersey, USS Missouri and USS Wisconsin have all become museum ships, while the USS Iowa is now in the reserve fleet, with the intention that she would be turned into a museum or memorial as well.

I could be wrong, but I believe I read somewhere, that there is a provision allowing the ships to be converted back to active service within a certain period of time, should they be needed during a wartime emergency.

... AGAINST ALIENS!

Well, the premise of the film is that those ships are participating in wargames when they happened to encounter aliens, so it's not an emergency requirement to begin with.