default of such trophies, the ship's papers would be accepted. In order to obtain such proofs of success the submarine had to rise to the surface and approach its victim. The search for food, especially for alcoholic liquor, was another motive that led to such a manoeuvre; and sometimes mere curiosity, the desire to come to close quarters and inspect the consequences of his handiwork, also impelled the Hun commander to take what was, as events soon demonstrated, a particularly hazardous risk. This simple fact that the submarine, even when the danger had been realized, insisted on rising to the surface and approaching the vessel which it had torpedoed, offered the Allies an opportunity which they were not slow in seizing. There is hardly anything in warfare which is more vulnerable than a submarine on the surface within a few hundred yards of a four-inch gun. A single, well-aimed shot will frequently send it to the bottom. Indeed, a U-boat caught in such a predicament has only one chance of escaping: that is represented by the number of seconds which it takes to get under the water. But before that time has expired rapidly firing guns can put a dozen shots into its hull; with modern, well-trained gun crews, therefore, a submarine which exposes itself in this way stands practically no chance of getting away. Clearly, the obvious thing for the Allies to do was to send merchant ships, armed with hidden guns, along the great highways of commerce. The crews of these ships should be naval officers and men disguised as merchant masters and sailors. They should duplicate in all details the manners and the "technique" of a freighter's crew, and, when shelled or torpedoed by a submarine, they should behave precisely like the passengers and crews of merchantmen in such a crisis; a part--the only part visible to the submarine--should leave the vessel in boats, while the remainder should lie concealed until the submarine rose to the surface and approached the vessel. When the enemy had come within two or three hundred yards, the bulwarks should fall down, disclosing the armament, the white battle ensign go up, and the guns open fire on the practically helpless enemy. II