The World Peril of 1910 by George Griffith

Happily for the defenders of Britain the fleet of aerial submarines, from which so much had been expected for offensive purposes during the proposed "triumphal march" on London, soon became of little or no use in the field.

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.