The naval cannon was similar in effect to a regular cannon, though it projected fire balls in an arc to cause wide-ranged damage. It was commonly mounted on a narrow craft with outriggers, and was particularly effective against the wooden sides and sails of ships.
Two people were needed to efficiently wield it, with one person steering the boat it was mounted on, and the other to aim and fire the cannon itself.
In Napoli during the early 16th century, the naval cannon's manufacturing was overseen by a man named Eduardo. Though he was given the responsibility to examine the finished product and make final adjustments, he did not approve of Cesare Borgia's plans for the weapon.
In 1502, after being sent by Leonardo to destroy his war machines, the Assassin Ezio Auditore da Firenze traveled to Napoli. He encountered Eduardo there, and was prepared to interrogate him, but Eduardo readily volunteered to lead him to the naval cannon, along with the schematics they had used to build it.
Upon clearing the dry dock of guards, Ezio flooded the area, and steered the naval cannon out into Napoli's harbor. Alternating between steering the boat and firing the naval cannon, the Assassin attacked several Borgia warships moored nearby, destroying a large number of them in the process.
Afterwards, Ezio directed the naval cannon to the center of the boat it was mounted on, and fired it; narrowly leaping into the water before the invention exploded.
- Successfully using and destroying the naval cannon granted the "Splash!" achievement.
- A miniature replica of the naval cannon could be found at the armory in the Tiber Island headquarters after completing the "Loose Cannon" memory.