Gaon Cannon is one of the stronger weapons that appears in the Anime and Manga series One Piece. It is one of the special armaments used by the Thousand Sunny, a ship of the Straw Hat Pirates. The name "Gaon" is probably from the Japanese term for a roaring sound: "gaō", fitting for a lion-themed ship.
This fearsome weapon is mounted in the figurehead of the Thousand Sunny, which is fashioned in the form of a lion's head. This cannon is the strongest weaponry available on the vessel and is known as one of its two special air cannons. Its front installation in the bow of the boat lets it have frontal attacks, so it's extremely vital for their ship's offense ability.
The power that the Gaon Cannon possesses is of an overwhelmingly great proportion, so much so that, when designing a ship, it needed to be taken into consideration. Franky, the shipwright of the Thousand Sunny, had to keep in mind the tremendous force it would unleash when he was constructing the vessel. Its power remains so overwhelming even though it was smaller compared to most battleship cannons; it can only be safely fired from a ship with the sturdiness of the Thousand Sunny.
It is in Episode 389 of One Piece, in the episode "The Sunny's Super-Secret Weapon: Gaon Cannon", where this weapon is firstly introduced. Herein, the outline about the capabilities of this weapon and the role it would play in the arsenal of the Straw Hat crew is delineated. There is an important introduction made for this cannon, as it is a "super-secret weapon" that could turn the tide of any naval battle in favor of its user.
The Gaon Cannon is not a single weapon alone but part of the whole system of defenses and offensive capabilities on the Thousand Sunny. There are sixteen cannons all over this ship, including seven traditional cannons from either side, in addition to the Gaon Cannon and another specialized air cannon. The result is a firepower that makes the Thousand Sunny formidable in the One Piece world.
As far as its operation goes, the Gaon Cannon is operated from a small room available in the bow of the boat. Such strategically placing permits perfect aiming and control over such a powerful weapon. Moments of critical juncture in the adventures of the Straw Hat Pirates often reveal its might as a trump card in fierce battles.
The Gaon Cannon is not the only special feature embedded in the Thousand Sunny. Another notable capability would be the "Chicken Voyage," said to be on the same ranking as the Gaon Cannon in referring to one of the ship's proud, hidden powers. These features establish the Thousand Sunny as one of the most high-tech and powerful ships in the world of One Piece.