So I had this idea for a crossover between the movie, The final countdown and the anime / manga zipang. Where it's both an American Navy ship as well as a Japanese Maritime Self-Defense Force ship That are teleported back in time to before Pearl harbor happens or right in the middle of the Pacific war.
At first, at the beginning of the training exercise, these people are buddy, buddy essentially, but after being transported where does the loyalty between these two sets of crew members stand? With their original countries which are now enemies in this timeline or to their allies who are once their enemies? You can imagine the tension these two ships would have in this hypothetical story.