That is a weapon from the American Civil-War era which was called a "torpedo." It was set on the end of a long wood or metal spar which was in turn mounted upon the bow of whatever vessel used for the attack. The attacking vessel would set out in search of another ship to sink, at which point it would go full-speed ahead and ram the barbed point into the wooden planking of the intended victim. The attacker would then back away, leaving the barb and explosive imbedded in the hull of the other ship. The lanyard would spool out from the attacker until it became taut, activating the trigger and exploding the warhead.
The torpedoes were most often mounted upon "semisubmersible" craft called "Davids," but the most famous torpedo-bearer was the full submersible H.L. Hunley, which in sinking the U.S.S. Housatonic, became the very first submarine to sink an enemy vessel in combat. Unfortunately, the Hunley itself also sank, and no other ship was sunk via submarine until the early days of World War I.