The correct input device for tank gunning is a horizontal and vertical wheel bolted to your desk that you turn with your hands at whatever speed you want the horizontal or vertical to move. Some tank designs are even so kind as to include smaller wheels for fine control.
A mouse closely emulates the gunner's ability to turn wheels quickly or slowly depending on how much movement he wants to make, however it is far too easy to aquire targets, especially on the move, and doesn't feel right.
A keyboard closely emulates the gunner's two sets of wheels if WASD is set to fast movements and arrows are set to fine movements. The right control can even be your fire key. However this setup forces movement at a certain speed when you press the button, which can result in difficulties aiming.
A solution is to incorporate more customization into the keyboard keys. Under the options menu, have a Turret Input panel. This has two sliders which can be adjusted in sensitivity for two sets of keys, one WASD, and one with the arrows. I could set my WASD keys to be very fast for maximum turning speed and my arrows to be very slow for the finest control, or my arrows only slightly slower if it suits my tastes, or even have WASD be fine control if I'd like to gun southpaw. This will also put both hands on the keyboard for commanding the gun, which just feels more mechanical than an ergonomic mouse.
The other solution is to get Logitech to come out with a fake breechblock input device that bolt to your desk. Then we'll see who's against having a loader position!