Assault Cruiser
The standard TDC ship of the line, the assault cruiser packs a lot of firepower into a conveniently sized (cheap) hull. Mounting six turrets, including a super-heavy dual beam turret, the Assault Cruiser is almost as heavily armed, and faster than its heavier cousin the Diplomat.
Beam Cruiser
The beam cruiser was designed for only one thing, and one thing alone, unloading a massive amount of focused energy into one small area. Whether said area is the hull of an alien battleship, or the crust of a rebellious planet is not something the designers of this ship bothered to specify.
Size Comparison Chart.
From top to bottom: Assault Carrier, Diplomat Heavy Cruiser, Beam Cruiser, Assault Cruiser, Negotiator Heavy Destroyer, GZG NSL Lutznow Class Destroyer.