Ancient Battleship Merkava

A cruiser-sized ancient battleship.
This was used in a great war and still few of them are activating around ruin on the planet.
People of Federation Academy estimate Merkava has 6580 times firepower of Federation Fleet's typical cruisers.

They don't appear around Empire and Federation's territory but in case of finding the ancient warship, Federation and Empire are supposed to destroy it together. This treaty is called "double headed operation". Empire and Federation are hostile each other, but they can be temporarily friend by easy theory of games.