The Cannonball is an obtainable item in Sea of Thieves.
It is used as ammunition for the Cannon.
Cannonballs can be found on almost all locations on the Map, they can be stored on the ship in the cannonball barrel and can be stacked 100 per barrel for a total of 300 stored. Cannonballs are the only projectile that can be fired out of the cannon besides players. Your player can hold 10 cannonballs on them at all time, unlike Banana and Wooden Plank where you can only hold 5 at a time.