There was nothing for it but for British valour to bow to the inevitable, and evacuate the town and what remained of its fortifications; and so with sad and heavy hearts the remnant of the brave defenders turned their faces inland, leaving Dover to its fate. Meanwhile exactly the same havoc had been wrought upon Folkestone and Deal. Hour after hour the merciless work continued, until by three o'clock in the afternoon there was not a gun left upon the whole range of coast that was capable of firing a shot. All this time the ammunition tenders of the aërial fleet had been winging their way to and fro across the Strait constantly renewing the shells of the war-balloons. As soon as it began to grow dusk the naval battle commenced. Numerically speaking the attacking force was somewhat inferior to that of the defenders, but now the second element, which so completely altered the tactics of sea fighting, was for the first time in the war brought into play. As the battleships of the League steamed out to engage the opponents, who were thirsting to avenge the destruction that had been wrought upon the land, a small flotilla of twenty-five insignificant-looking little craft, with neither masts nor funnels, and looking more like half-submerged elongated turtles than anything else, followed in tow close under their quarters. Hardly had the furious cannonade broken out into thunder and flame along the two opposing lines, than these strange craft sank gently and silently beneath the waves. They were submarine vessels belonging to the French navy, an improved type of the _Zédé_ class, which had been in existence for more than ten years.[1] These vessels were capable of sinking to a depth of twenty feet, and remaining for four hours without returning to the surface. They were propelled by twin screws worked by electricity at a speed of twenty knots, and were provided with an electric searchlight, which enabled them to find the hulls of hostile ships in the dark. Each carried three torpedoes, which could be launched from a tube forward so as to strike the hull of the doomed ship from beneath. As soon as the torpedo was discharged the submarine boat spun round on her heel and headed away at full speed in an opposite direction out of the area of the explosion. The effects of such terrible and, indeed, irresistible engines of naval warfare were soon made manifest upon the ships of the British fleet. In the heat of the battle, with every gun in action, and raining a hail of shot and shell upon her adversary, a great battleship would receive an unseen blow, struck in the dark upon her most vulnerable part, a huge column of water would rise up from under her side, and a few minutes later the splendid fabric would heel over and go down like a floating volcano, to be quenched by the waves that closed over her.