the periscope above the water whenever desired. This speed was so very slow—about one mile an hour—that it could be kept up an entire day without exhausting the electric batteries.
The net result was this: The German submarine necessarily sailed most of the time on the surface with its conning-tower and deck exposed, whereas the Allied submarine when on its hunting grounds, spent all of the daylight hours under water, with only the periscope visible from time to time for a few seconds. Just as the German U-boat could "spot" an Allied destroyer at a great distance without being itself seen, so could the periscope invariably see the German submarine on the surface long before this tiny object came within the view of a U-boat conning-tower. Our submarine commander could remain submerged, sweep the ocean with his periscope until he had picked up the German enemy; then, still under water, and almost invariably unseen, he could steal up to a position within range, and discharge a torpedo into its fragile side. The German submarine received that same treatment which it was itself administering to harmless merchantmen; it was torpedoed without warning; inasmuch, however, as it was itself a belligerent vessel, the proceeding violated no principle of international law.
II
The Allied submarines, like many other patrol craft, spent much of their time in those restricted waters which formed the entrances to the British Isles. Their favourite places were the English Channel, St. George's Channel, which forms the southern entrance to the Irish Sea, and the northern passage-way between Scotland and Ireland. At these points, it may be remembered, the cargo ships could usually be found sailing singly, either entirely unescorted, or escorted inadequately, while on their way to join a convoy or to their destinations after the dispersal of a convoy ; these areas were thus almost the only places where the German submarines had much chalice of attacking single vessels. The territory was divided into squares, each one of which was indicated by a letter; and the section assigned to each submarine was known as its
