Cope's Defense Mod (CDM) is a work-in-progress modification for Dawn of War II. The newest version is 0.5. The goal in CDM is to survive as long as possible against the waves of enemies (currently 40 waves, more to come) with the Space Marine squads (scouts, Tactical Marines, Assault Marines, Heavy Bolter, Apothecary and Techmarine, Force Commander) you receive in the beginning. You can upgrade your squads to be stronger and more effective. Still WIP but you can already download a playable version (which actually is lots of fun).
This shield is _very_ useful. It makes your squad totally immune (!) to ranged attacks and absorbs some damage in melee. Each hit taken in melee will reduce the squads' energy and as soon as the energy hits 0, the shield will disappear.