Thrust. Forcing thrust. Against earth. Earth. Earth cracking. Unburrowing from earth. Unburrowing and cracking. Unburrowing and cracking with force. Forcible entry, forcible defeat, forcible, forcible, forcibl-l-l-l-l-eeee...
Crash?
Forcible crash? No.
Oh, wait! No. Yes! No. Might as well, got nothing else here.
Seigent (Seige+Sergeant)? Meh. Worth a try.
Earth.

: Force (Forcible Ascention? Hmmmmeh.) Burrow for one turn. On re-entry, %chance to break opposing shield.
Ability:

: Force: Burrow for one turn. On re-entry, % chance to destroy opposing shield.
The % wouldn't have to be very large, just enough so that it'd take a couple tries.
Or five all at once. Either one works.