These artillary cannons would be massive structures, built in a specialized crafting table made for building large weapons. (sort of like the planes mod, where in order to craft that big plane you need a bigger crafting table, this is the same concept)
the cannon would be a large "vehicle" that you would right click to get in, and then move you're mouse to control. When in the vehicle, there would be 2 screens, one of them showing the barrel of the cannon, and the other one showing the area that the shell would hit.
Thats basically it, it would shoot massive shells and well, kaboom, WW2 style.
Instructions for using:
-Build in the crafting table (i do not have recipes)
-right click on a block to set it down (it would be a really big cannon, like the AA guns from the planes mod but way bigger)
-aim the cannon
-left click to shoot!
Thats pretty much it. It might be impossible to do but i figured i'd suggest it anyway since we need some more weapons 
