According to Army Technology, the M777 Howitzer, the standard cannon deployed by American ground forces, has a range of 15.3 miles with standard shells and 24.8 miles with rocket-assisted ammunition. American naval guns reach up to 25 miles as well.
A cannon consists of a strong steel tube that is sealed on one end. Gunpowder is loaded into the sealed end of the tube and a projectile, usually a cannon ball or an artillery shell, is loaded into the other end. When the gunpowder is lit, the ensuing explosion creates a force that pushes the projectile out of the tube at a very high speed, propelling the projectile for miles.