Protection against these weapons was offered by Destroyers in convoys.  
During the Civil War, E. C. Singer developed one of these things that attached to a 40-foot-long pole known as the "spar" variety.  The first modern example of one of these devices was powered by a tank of compressed air, had tapered ends, and was designed for the Austro-Hungarian Empire by the Englishman Robert Whitehead.  During World War II, the Japanese developed extremely (*) fast versions of this weapon known as the "long lance", which also contained a deadly magnetic pistol.  While brainstorming how to defend the Philippines from an enemy attack, Bradley A. Fiske invented the aerial form of these weapons.  The automatically-adjusting horizontal rudders on these weapons were eventually replaced by gyroscopes to keep them at a consistent depth.  Protection against these weapons was offered by Destroyers in convoys.  For 10 points, name these principle weapons of U-Boats.
During the Civil War, E. C. Singer developed one of these things that attached to a 40-foot-long pole known as the "spar" variety.  
naval torpedoes [or spar torpedoes or locomotive torpedoes; do not accept "naval mines"]