[Krsqk]

I don't think an armor-piercing mortar round is possible (although I could well be wrong). The ballistic use of RPGs is even more unlikely. You'd either have to fire at a high angle to hit your target, giving your round a high probability of being misdirected by wind; and/or you'd have to cut the burn time down for the rounds so they wouldn't go so high first.

If someone does come out with an effective means of attacking the top armor of the tanks, I'm sure the defense industry will find some way to stop it. It's the old "Make a bullet to pierce this armor" "Okay, now make some armor to stop this bullet" routine.