[Illustration: FIG. 32.--Diagram illustrating the Dover lighted barrage. This barrage consisted of two lines of lightships, _E_ and _F_, from England _A_ to France _B_. The first line extended from Folkestone _C_ to Cape Gris Nez _D_. The second line _F_ was situated seven miles westwards of the first line. The small top diagram shows how the two pathways of light, with a numerous patrol between, compelled the U-boats to dive in order to avoid observation and destruction by gun-fire. The lower diagram shows the deep-laid mines arranged to receive the U-boats when they attempted to run the blockade in a submerged condition.] By this means the only avenues by which hostile submarines could hope to pass on the surface through the barrage at night were the dark lanes of water between the lightships. It was these points which were closely guarded by strong patrol flotillas, whose duty it was to attack submarines attempting to get through and, with the aid of guns and depth charges, to force them to dive below the surface. Here certain destruction awaited them on the submerged mine-fields. If, however, one line of defence was safely passed by a hostile submarine, there was another to be negotiated seven miles farther on, and once a submarine got between the two lines her chances of escape were indeed small, for whichever way she turned the surface would be covered with fast patrol craft and at night lighted by the rays of many searchlights, while the under-seas were almost impassable with mines. If, however, notwithstanding these defensive systems, a submarine succeeded in passing through and getting to work on the lines of communication with the armies in France, there were hydrophone organisations and patrols all down the Channel from the lighted barrage to the Scilly Islands. By this means a U-boat would be seldom out of the hearing of these instruments for more than an hour or so at a time. The success which attended the perfecting of this vast system was such that German submarines based on the Flanders coast gave up attempting to pass down the English Channel. They tried to go to and from their hunting grounds on the Atlantic trade routes round the north coast of Scotland. Here the great northern systems took their toll. During the first nine months of the year 1918 the German submarine flotillas at Zeebrugge and Ostend lost thirty vessels, and no less than fifteen of these had, at the time of the signing of the Armistice, been discovered lying wrecked under the lighted barrage. CHAPTER XIV OFF TO THE ZONES OF WAR HITHERTO I have dealt with the scientific training of the personnel, the armament and the general organisation of the anti-submarine fleets, leaving it to the imagination of readers to invest the bare recital of facts with the due amount of romance. If, however, a true understanding of this most modern form of naval war is to be obtained, the human aspect must loom large in future pages.