If you can't accept that an older unit occasionally beats a newer unit for better playbalance, and if you're fine with a caravel being around 500 yrs. without some bright thinker toting a few missiles aboard, then you can use the included editor to make the newer units progressively tougher.
The defualt BB has an attack of 18, IIRC, and the Caravel has a defense of 2. If that 0.00001 chance (if I did my math right) of the BB loosing is too much for you, just up the BB's stats.
I said "better playbalance" above. In this case I mean "Less realistic, but more challenging." And its not like Civ is "realistic" anyway. It isn't a wargame, and it isn't a sim. Part of the fun is that it feels a bit like both, but you can't have a game be as simple and broad as Civ and expect it to also be as accurate and realistic as, say, TOAW or Decisive Action.
In CivII I usually won through a military victory, and much of that was because I could get a tech edge and just roll over my less-advanced foes. I like the way it works in CivIII better - much more challangeing. A tech edge still makes you very tough, but you'll have a real fight in front of you.
I've fiddled with the combat stats of most of the modern units myself, but so that the realtionships between the modern units is more to my likeing. An old unit will still rarely beat a more advanced unit - just part of the game. Groan, curse, and accept it - If anyone goes to the trouble to revamp the combat system so that it's "realistic" I've got a copy of TOAW I'd like to sell you - I also want to see your redone economic system for CIv3.
