It seems that 30,000 pounds of bomb isn't enough for the USAF:
Pentagon: 30,000 Pound Bomb Too Small - Slashdot
Looking at pictures of the thing, I would have thought the fins and paddle-thingies on the back end would cause serious drag issues.
After all, you only need to get close enough I would have thought and was the design principle behind Barnes Wallis's original idea.