countered such a step by sending back from the war zone an adequate number of craft to protect convoys in and out of the Atlantic ports, in the same manner that convoys were protected in the submarine danger zone in European waters. This is a fact which even many naval men did not seem to grasp. Yet I have already explained that we knew practically where every German submarine was at any given time. We knew whenever one left a German port; and we kept track of it day by day until it returned home. No U-boat ever made a voyage across the Atlantic without our knowledge. The submarine was a slow traveller, and required a minimum of thirty days for such a trip; normally, the time would be much longer, for a submarine on such a long voyage had to economize oil fuel for the return trip and therefore seldom cruised at more than five knots an hour. Our destroyers and anti-submarine craft, on the other hand, could easily cross the Atlantic in ten days and refuel in their home ports. It is therefore apparent that a flotilla of destroyers stationed in European waters could protect the American coast from submarines almost as successfully as if it were stationed at Hampton Roads or Newport. Such a flotilla would be of no use at these American stations unless there were submarines attacking shipping off the coast; but as soon as the Germans started for America a fact of which we could always be informed, and of which, as I shall explain, we always were informed—we could send our destroyers in advance of them. These agile vessels would reach home waters about three weeks before the submarines arrived; they would thus have plenty of time to refit and to welcome the uninvited guests. From any conceivable
point of view, therefore, there was no excuse for keeping destroyers on the American side of the Atlantic for "home defence." Moreover, the fact that we could keep this close track of submarines in itself formed a great protection against them. I have already explained how we routed convoys entering European waters in such ways that they could sail around the U-boat and thus escape contact. I think that this simple procedure saved more shipping than any other method. In the same way we could keep these vessels sailing frm American ports outside of the area in which the submarines were known to be operating in our own waters.
Yet the enemy sent no submarines to our coast in 1917;
