modular freighters

http://www.tonyfrancis.free-online.co.uk/Brigade/sfs/pics/SFS038.jpg

The modular freighter with the rigid spine

http://www.tonyfrancis.free-online.co.uk/Brigade/sfs/pics/SFS039.jpg

outfitted as a merchant fighter carrier

http://www.tonyfrancis.free-online.co.uk/Brigade/sfs/pics/SFS040.jpg

outfitted as a merchant auxilliary (armed merchantman)

These fit the model described - containers easily attached/removed,
keeping the control systems as part of the shp spine. In wartime,
containers can be replaced with fighter launch rails, strikeboat tow
anchors, or weapons stations.

<This was, by the by, a totally unsolicited plug... this is a nice mini
concept.>

Someone asked about non-ftl towing? What's the big deal? Make sure your
drive is rated for it. Then just calculate thrust based on the combined
mass of the tug + towed entities. You might want to limit the mass of
the towed package to say something like 1 tug mass or 2 tug masses. Or
maybe 5. Whatever seems right - just so's the tether/control line
doesn't require such a brutal level of signficance.

For reasons aforementioned about the difficulty of control, I believe
the container ship far more sensible. Towing would probably be
restricted to small tugboats working in teams to move disabled or
damaged supertankers or container ships. At the very least, each
individual towed entity would have to have an "emergency breakaway" kit.
This kit would allow a captain to jetison it for more thrust, and would
immediately decelerate the object to speed 0 (for safety in inhabited
systems!). There would, similar to the modern road grid, definitely be a
"maximum safe speed" for these beasties, and you'd need special
licenses.

Except for moving some barges, we rarely use this method today. We
generally have container ships that are far more able to react to
conditions around them than a barge chain for transporting our cargoes.
Garbage moves on barges, so might coal. TVs don't. Least I haven't ever
seen them moved thus.

Anyway, it is an interesting discussion to be sure.