In the late 1800s, the invention of the self-propelled torpedo incited a revolution in ship design. Navies needed new vessels to fire them and to defend against them. Enter torpedo boats–fast, lightweight ships that would play a big role in both World Wars. Examine some of these sophisticated speedsters, from the German S-boats, which turned one D-Day rehearsal into a very real battle, the MTB 102, the smallest vessel to ever serve as a Royal Navy flagship, and the PT 109, which made a hero of a young JFK.