[Strategia_In_Ultima]

Those things would be VERY dangerous, especially if you either
-use a Destroyer sized ship or something or
-mod in small warhead components.
The fast, tough little ships that are hard to hit can be a real threat to the massive warships as the smaller ships can dart in at a Dreadnought or something, and then ram it for a lot of damage. What you could also do is design a Frigate with one or two warheads, the command & control components, the max amount of engines and then fill it up with (emissive) armor. They could be produced in droves as a result of their small cost, and would be extremely effective defenses against orbital bomber raids, as orbital bombers tend to be big ships. Say, three Battleships with Planetary Napalm and an escort Dreadnought with anti-ship weapons (and a to-hit offense and defense penalty) enter orbit over one of your planets with these defenses. You swarm the escort DN's defenses, and completely obliterate it, leaving the orbital bombers very vulnerable to not only the ramming ships (which you could also choose to save for another fight), but also to defense stations and/or satellites and fighters.

Hmm..... gotta put this in Capship..... small kamikaze ships that are more lethal to a Dreadnought-sized ship than a COMCA, while the large capships are the only ships truly capable of attacking planetary defenses.....

But you know, the first thing that sprang to mind after reading your original post was "Leaky Armor". It'll do pretty much what you say you want.