The Oto Melara was an anti-ship anti-missile anti-air and anti-land 76mm gun developed by the italian army. It was designed to be small enough to mount on a ship. In-game this is a 3 block tall gun. It may look small on the picture but it is quite big actually.
In-game this gun can fire 16 shots before overheating and needing a cool-down. This gun is quite powerful if used correctly. If you want to destroy this cannon you must aim for the lower parts of the main body as that is were the hit-boxes are.