Appearance and Design
The King Cannon is a four-wheeled tank with a giant cannon barrel that resembles a screw mounted on it, decoratively designed with the four card suits (spade, heart, club and diamond). On the left side of the tank is a meter gauge that shows how much charge is achieved before the cannon can be fired, and the back is a feed ramp for the giant bullet-shaped cannonballs with drill-design.
The cannon can fire its bullets with drilling force, which is strong enough to cause intense impact to create shock waves that can spread throughout a portion of the ocean. When deflected, the vibrational force was enough to shatter a thick sheet of tempered glass.
When the Trump Siblings took over Clockwork Island years back, they forced the scientists there to create the King Cannon, so as to provide the ultimate weapon for Bear King to become the Pirate King.
Clockwork Island Adventure
When the Straw Hat Pirates arrived onto Clockwork Island and defied the Trump Siblings, the King Cannon had reached its completion stage. Bear King had the Hyena Three unveil it, preparing to kill three of the captured Straw Hats with it as a demonstration, but was interrupted by Monkey D. Luffy before he could actually open fire.
During Luffy's battle with Bear King, Borodo aimed the cannon at the distracted Bear King, but missed by a margin, resulting in the distant sea to be hit instead; the shock waves from the impact can be felt all the way back to the battlefield. Bear King got angry that his cannon was being used by someone else, and shot at Borodo for it, only for Akisu to take the bullet.
When Luffy finally managed to injure Bear King with sheer brute force and perseverance, Bear King immediately got the King Cannon back up straight and fired a cannon shell at him. Luffy used his rubber powers to create a counter force to send the drilling bullet back at Bear King, who managed to prevent the projectile from penetrating his rock-hard defense. However, the vibrations from the spinning bullet caused the tempered glass ground which the cannon stood to shatter, thus dropping the weapon and its wielder into the abyss, leading to the remaining ammunition to explode, which destroyed Clockwork Island's "key", the King Cannon and Bear King all in one blast.
- One Piece Movie — Clockwork Island Adventure, Bear King utilizes the King Cannon in an attempt to kill the Straw Hats.