The Harpoon Gun is a light weapon with two firing modes. The first fires the Harpoon without the rope, which simply deals damage. The second fires it with the rope, which can grapple enemy ships. Grappling enemy ships is a prerequisite to boarding.
The rocket-powered Harpoon is one of the oldest, and most effective weapons used among the space-faring races. It is fired into the side of an enemy ship, embedding itself in the hull, and explodes doing serious damage. Doubly useful, a Harpoon Gun can also fire a Harpoon with a cable attached. These Harpoons are used to grapple onto other ships during battle. Grappled ships can be prevented from sailing out of danger or can even be boarded!
The Harpoon Gun is the only weapon in the game that deals more damage against iron than against wood, however this is only true when it isn't used to grapple, if it is, then it does less damage against iron than wood.
For some reason, the Harpoon Gun deals extremely high damage to Dragons.