In the late 1970s, the BDM Corporation did a study for what a plausible space warship could look like (thanks to the invaluable Atomic Rockets for its analysis).

It has a spin-gravity crew quarters, is powered by nuclear reactors, and its armament consists of a laser in a de facto turret, a forward facing railgun, and a rear-facing particle beam (because the radioactive particles can’t risk hitting the ship).

The Space Shuttle in the picture is for scale-the whole thing is about two hundred meters long!