I mean, the movie is called Battleship, and it's about the game Battleship, where players try to sink each other's Battleships. But the Navy doesn't have Battleships anymore, so they are going to start the film on the last floating Battleship which has been mostly decommissioned, along with the aged-but-spry retired Battleship crew who would love one last hurrah.
It's like if they made a movie called Chekov's Gun, and the movie starts by showing you a Gun hanging on the wall with "Property of Chekov" engraved in the stock, and everyone stops to ponder if maybe Chekov's old Gun would still fire if they needed it.