The Last Ranger: Warship

The Rangers, built to defend the Regency, destroyed it, sending galactic civilization back to the pre interstellar age.
A thousand years later, a group of civilians stumble across the wreck of one, buried under tonnes of rock. It's intact, still on, and the malevolent, insane AI it holds is still alive.
Only this AI is like no other, and when the planet is threatened by dangerous space pirates, it offers the frightened populace a deal,
Free it from it's hell, let it roam the stars again, and this demon will serve them....