A non-starship specifically intended for defensive operations inside a star system. Developed on the principle that a non-starship (because of the increased armament made possible by its lack of jump drives) can normally defeat a starship of equal tonnage. SDBs are typically stationed at the vital points of a system (the gas giants, the asteroid belt, the major world, and so on) and attack invading vessels according to one or more predetermined plans.
System Defense Boats range in size from 100 to 5000 tons and are constructed at all tech levels from 8 to 15. There are hundreds of different types, depending upon the specific mission for which they are designed.
Because SDBs have no jump drives, shifting them from system to system can be a problem. Some types have jump shuttles which fit to the craft and provide jump capability. Another method is simple transport in large bulk cargo containers; The SDBs are loaded into 10,000-ton or 20,000-ton bulk carriers for the multi-parsec journey. This method, of course, is not recommended if immediate combat is expected at the destination.