SFB Tugs etc.
In SFB, in addition to the extremely slow freighters, there are "line" warships converted to a cargo carrying role. Tugs and Light Tactical Transports (LTTs).
The original tug was from the Franz Joseph Technical Manual (the Ptlomey). Notice how it looks like a cruiser with a giant pod slung / towed underneath. SFB created "pallet", which fulfill the same role as pods for certain races.
These pods are normally bulk-freight carriers, but someone designed pods filled with such things as weapons, fighter hangers, power systems, etc.
When these special pods are fitted to the tugs, you get the "special" tugs like battle tugs (carrying battle pods), carrier tugs (with hanger pods), etc.
Monitors:
Special ships designed to have DN level firepower. Due to cost-saving measures, the engines are barely capable of moving the ship. They are normally towed to an important system where they are assigned system-defense duties. If a monitor was theoretically sent on a fixed-position assault or an escort mission, the monitor is so slow that it would take forever to get to the target / destination...