The submarine was unleashed on an unsuspecting world in 1914 with devastating consequences for its victims. Its development since the turn of the twentieth century had been treated contemptuously by conventional naval opinion. Yet it proved to be a weapon of potentially decisive power. This book traces the development of the submarine, explaining the technical and doctrinal issues that had to be overcome. It goes on to detail and examine the use of the submarine in World War One, focusing on the severe divisions of opinion in the German command as to whether to use their U-boats against British shipping and the consequent British reaction. Admiral Jameson served for twelve years in submarines and through his own experiences and some diligent historical research has written a definitive history of the dawn of the submarine as a mighty weapon of war.