Free Labor Diguised as a Contest: Huge Gun

Basically I need a big gun. A BIIGG one. see the borders.

Rules:

It can shoot anything you want, but having more than one shot/being reloadable is preferable.

It doesn't have to be exactly that size; it can be bigger or smaller, but it's a guideline.

Must be controllable using standard signal cables.

May not use wireless transmission. (There's plenty of space of 8-splitters.)

Must be mobile. I'm planning to attach it to a vehicle.

Must be aimable. (to a fair extent. I don't need full 360.)

Must be officially posted as a derivative by 6/25/2015.
How's this for a BIIIIG gun!