This cannonball was used as ammunition in a muzzle-loading cannon: a weapon in which the projectile and the propellant (the substance used to propel the projectile at great speed) are loaded through the cannon's muzzle.
Made of solid iron, the weight of the cannonballs that a cannon could fire determined its caliber. So a 12-caliber cannon would fire 12-pound cannonballs, with an approximate diameter of 4.7 inches.
Cannonballs were used to pierce the wooden hulls of enemy ships, causing splinters of wood and shrapnel to fly around the deck. This was what actually caused the majority of wounds and casualties in naval battles.