The WP barrage you get at vet 1 is lovely, especially its range. The WP and HEAT barrages have double the range of the auto-fire, so I often toss willy pete on a BG HQ to force them to back off of it.
Also I don't know how many other people realize this, cause I didn't until a couple months ago, but the HEAT barrage does a full 160 dmg to tanks if it hits. Only 3 shells but its pretty accurate with LOS so you can really put a hurt on some of the slower and larger targets in the game if you place it right.
I did not know that! Great info!