I've just finished a particularly nasty mission - where, to start with, I was hindered by mountains on the east side of the map, and there was a big cannon think in the middle, which attacked everything within range each turn reducing the health of each unit by half. Nice.
I built up a massive force, of bombers and tanks, and took them into the centre, bombing the anti-tank guns and shooting the missile launchers, avoiding the interceptors and rocketing their megatank. I was all ready to attack the HQ after destroying the big cannon - but once that went down (after one megatank strike and one bombing) it was mission over. Run away, fools!