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.
But as if it were not enough that the defending fleet should be attacked from the surface of the water and the depths of the sea, the war-balloons, winging their way out from the scene of ruin that they had wrought on shore, soon began to take their part in the work of death and destruction.
Each of them was provided with a mirror set a little in front of the bow of the car, at an angle which could be varied according to the elevation. A little forward of the centre of the car was a tube fixed on a level with the centre of the mirror. The ship selected for destruction was brought under the car, and the speed of the balloon was regulated so that the ship was relatively stationary to it.
As soon as the glare from one of the funnels could be seen through the tube reflected in the centre of the mirror, a trap was sprung in the floor of the car, and a shell charged with dynamite, which, it will be remembered, explodes vertically downwards, was released, and, where the calculations were accurately made, passed down the funnel and exploded in the interior of the vessel, bursting her boilers and reducing her to a helpless wreck at a single stroke.
Every time this horribly ingenious contrivance was successfully brought into play a battleship or a cruiser was either sunk or reduced to impotence. In order to make their aim the surer, the aerostats descended to within three hundred yards of their prey, and where the missile failed to pass through the funnel it invariably struck the deck close to it, tearing up the armour sheathing, and wrecking the funnel itself so completely that the steaming-power of the vessel was very seriously reduced.
All night long the battle raged incessantly along a semicircle some twelve miles long, the centre of which was Dover. Crowds of anxious watchers on the shore watched the continuous flashes of the guns through the darkness, varied ever and anon by some tremendous explosion which told the fate of a warship that had fired her last shot.
All night long the incessant thunder of the battle rolled to and fro along the echoing coast, and when morning broke the light dawned upon a scene of desolation and destruction on sea and shore such as had never been witnessed before in the history of warfare. On land were the smoking ruins of houses, still smouldering in the remains of the fires which had consumed them; forts which twenty-four hours before had grinned defiance at the enemy were shapeless heaps of earth and stone, and armour-plating torn into great jagged fragments; and on sea were a few half-crippled wrecks, the remains of the British fleet, with their flags still flying, and such guns as were not disabled firing their last rounds at the victorious foe.
To the eastward of these about half the fleet of the League, in but little better condition, was advancing in now overwhelming force upon them, and behind these again a swarm of troopships and transports were heading out from the French shore. About an hour after dawn the Centurion, the last of the British battleships, was struck by one of the submarine torpedoes, broke in two, and went down with her flag flying and her guns blazing away to the last moment. So ended the battle of Dover, the most disastrous sea-fight in the history of the world, and the death-struggle of the Mistress of the Seas.