Fragmentation mortar and/or round.

[ClayOgre]

You can lob these over buildings, the land and burst, whacking everything within a server specified kill radius. Controlled by the fire key. the longer you hold it down, the further away your round gets lobbed. Aiming might be controlled by a crosshair appearing in your radar, showing distance out from your tank.

Alternatively, you could also make just a plain frag round. Whatever you shoot, whether a tank or a building, the round fragments and sprays deadly shrapnel for a specified radius. Kinda almost like a remote version of shockwave. The mortar version would probably be more balanced, since the tank would have to be almost still to use it, and could not shoot directly ahead, only in an arc.

[Sharpshooter]

So you mean like holding down the fire button getting the round as far as you want, then when you release it it drops down or something? I kinda see what you mean, and I think its a pretty good idea.

[M1A2AbramsTank]

Soooooooooooooo it's like the variable _shotsKeepVerticalVelocity except they go down like an artillery or mortar shell? I think that would be a great idea!