I really don't see what kind of threat the Rapier is. In my opinion it's too damn slow compared to the Lightning.
It's perfectly logical for the AI to send them out on suicide runs, after all it doesn't have to bother about losses like the player does.. heck, it's a machine; it can't. So the Lightning, all though not a neccessaily difficult opponent, outranks the Rapier in my book.
Anyway, when your own ship gets too fast for torpedoes, the AI tends to stop using them totally.
It's really a rather nice thought; the AI saves its torpedoes until they're needed the most. However, they're much better suited against another computer. If the AI doesn't fire all of it's weapons against you it simply means you get more breathing room, right?
The rebel destroyer seems to be the ship best suited for the AI to use. It has all those nice guns for all purposes, missiles, torpedoes, heavy rockets and proton turrets. Come to think of it, so does the Kestrel if you count it's escorts.
I'm out.
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Here's something funny: System 7.5.2