FOUND IT!
After 3 hours of slowly checking every title in Wikipedia's list of DOS games, halfway through the O's I hit the jackpot.
"Obliterator"
http://en.wikipedia.org/wiki/ObliteratorWhile that is definitely the game, the screenshots are all from the Amiga version, and I'm almost positive I played the IBM version.
How the hell am I going to find a copy of that?
EDIT:
Nevermind! Ebay is swarming with $5 copies. All I have to do is crack out the 'ol floppy drive.
I found a few abandonware sites hosting it as well, but I wasn't sure if it had actually been legitimately released into the wild yet. Considering Psygnosis has been a part of Sony since '93 (
http://www.giantbomb.com/psygnosis-limited/65-448/) I think I'm just going to bite the bullet and order a hard copy.
Here are some screen shots of the game as I played it 18 years ago.