HE is not very effective against armored vehicles, unless you get a direct hit or a very near miss. However, the blast and fragmentation effects can destroy external mounted stores, blow off radio attennas, and damage optics, rangefinders, etc.
DPICM and BBDPICM is more effective against armored vehicles and this is probably what the OPFOR is using against you. The munitions use a small shaped charge to defeat the top armor of vehicles, which is why you will see photographs of T80 and other vehicles with reactive armor on the top of the turret.
If my memory recalls, the DPICM shaped charge can penetrate 4 inches of top armor.
And since we are discussing artillery vs vehicles, in the event that Cpt Proctor reads this - whatever happened to SADARM? Last I heard, it was in development but that was some years ago. Did it ever make it into inventory of the US military or did the project get cancelled at some point.
