Though the term ‘torpedo’ has been used for centuries to describe underwater mines, the modern torpedo, i.e., a self-propelled explosive device, was first developed in the mid-19^th century.  They were first deployed on ships twenty years later as issues such as speed, depth, and directional control continued to be worked on.  By World War I, the torpedo was in common use by all combatants, being fired from surface, subsurface, and air vessels.