Because of the uncertainty and danger of depending on underwater caches and tenders, each blockader usually returned at the end of two or three weeks to Heligoland, Zeebruge, Ostend, or some other base to take on supplies, report progress and rest the crew. This of course reduces the number of submarines actually on guard. How large that number may have been at any particular time since the blockade began is unknown to everybody except a few persons in Berlin. At the outbreak of the war, Germany had between twenty and twenty-five submarines in commission and a dozen or so under construction. If, as is claimed, the Germans have been completing a new undersea boat every week since the war began, that would have given them by August 1, 1915, a flotilla of seventy-seven, exclusive of losses. If only thirty had been lost, that would have left fewer than fifty submarines to blockade more than fifty seaports, great and small, scattered over more than twenty-five hundred miles of coast. Moreover, these widely scattered blockaders would have to be on duty by night as well as by day. But at night or in fog the periscope is useless; to intercept an incoming steamer, running swiftly and without lights, the submarine must rise and cruise on the surface. It cannot use a searchlight to locate the blockade-runner without consuming much precious voltage and at the same time attracting the nearest patrol-boat. The same disadvantages apply to sending wireless messages from one blockading submarine to another. And as the wireless apparatus of an undersea boat is necessarily low-powered and has a narrow radius, while “oscillators,” bells, and other underwater signaling devices are still in their infancy, it would seem as if the German “U-boats” in British waters must have been suffering from lack of coöperation and team-play. If the captain of a Union gunboat, lying off Charleston during the Civil War, caught a glimpse of a blockade runner, he could alarm the rest of the fleet with rockets and signal guns, but the commander of the _U-99_ off Queenstown cannot count on his consorts if he himself fails to sink an approaching liner. Perhaps the most notable shortcoming of the submarine blockade has been its failure to inspire terror. Contrary to the expectations of nearly every forecaster from Robert Fulton to Conan Doyle, the sinking of the first merchant vessels by submarines failed to frighten away any others. Cargo rates are high in war-time and insurance covers the owners’ risk, so few sailing orders were canceled. As for the captains, they are not noted for timidity, and professional pride is strong among them; most of them have families to provide for, and every one of them knows that behind him stands an eager young mate with a master’s ticket, ready to take the risk and take out the ship if the skipper quits. So the merchant marine accepted the submarine as one of the risks of the trade.