The torpedo was the greatest single game-changer in the history of naval warfare. For the first time it allowed any small, cheap torpedo-firing vessel – and by extension a small, minor navy – to threaten the largest and most powerful warships afloat. ROGER BRANFILL-COOK is a qualified battlefield guide, a professional translator from French, and also a writer on military subjects. His most recent book was X.1: The Royal Navy's Mystery Submarine, published in 2013