The reason was this: As, day after day and week after week, that awful struggle continued, it became absolutely necessary for the Allies to obtain men and material to make good the fearful losses which the valour and devotion of what was now a whole nation in arms had inflicted upon them, and so all but four were despatched to guard the route between Dover and Calais--eight under the water and eight in the air--and so make it possible for the transports to cross. Of course, this meant that thousands of fresh men and hundreds of horses and guns could be poured into Kent every day; but it also meant that the greater portion of the defenders' most terrible foes were rendered harmless--and this was not the least of the good work that the _Ithuriel_ had done. Of course, that famous "sea-devil," as the invaders called her, was mostly on the spot or thereabouts, and every now and then a crowded transport would lurch over and go down, or a silent, flameless shot would rise up out of some unknown part of the waters and a shell would burst with a firmament-shaking concussion close to one of the airships--after which the airship would burst with a still more frightful shock and distribute herself in very small fragments through the shuddering atmosphere; but this only happened every other day or so, for Erskine and his lieutenant knew a good deal better than to run too many risks, at least just now. So, for twelve weeks of bitter, bloody and unsparing strife the grim, unceasing struggle for the possession of the Capital of the World went on, and when the eighteenth of March dawned, the outposts of the Allies were still twelve to fourteen miles from the banks of the Thames. How desperate had been that greatest of all defences since man had made war on man may be dimly guessed from the fact that it cost the invaders two months of incessant fighting and more than a million men before they planted their guns along the ridges of the North Downs and the Surrey Hills. Meanwhile Gilbert Lennard passed his peaceful though anxious days between Bolton and Whernside, while Auriole, Margaret Holker, Norah Castellan and Mrs O'Connor, with hundreds of other heroines, were doing their work of mercy in the hospital camps at the different bases behind the fighting front. Lord Westerham, who had worked miracles in the way of recruiting, was now in his glory as one of General French's Special Service Officers, which, under such a Commander, is about as dangerous a job as a man can find in the whole bloody business of war. And still, as the pitiless human strife went on with its ceaseless rattle of rifle fire, and the almost continuous roar of artillery, day by day the Invader from Space grew bigger and brighter in the great reflector, and day by day the huge cannon, which, in the decisive moment of the world's fate, was to do battle with it, approached completion.