Happily for the defenders of Britain the fleet of aËrial 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.

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.

At midnight on the twelfth of March Tom Bowcock had announced that all was ready for the casting. Lennard gave the order by electric signal. The hundred converters belched their floods of glowing steel into what had once been Great Lever pit; night was turned into day by a vast glow that shot up to the zenith, and the first part of the great work was accomplished.

At breakfast the next morning Lennard received the following cablegram from Pittsburg:

"All ready. Crossing fourteenth. Give particulars of comet away when you like. Pittsburg Baby doing well. How's yours?—Parmenter."

In order to understand the full meaning of Mr Parmenter's curt cablegram it will be necessary to go back for a little space to the day when he made his hurried departure from the Clyde in the Minnehaha. It will be remembered that he had that morning received a cablegram from New York. This message had read thus:

"Complete success at last. Craft built and tried. Action and speed perfect. Dollars out, hurry up.

"Hingeston."

Now the signer of this cablegram, Newson Hingeston, was an old college friend of Mr Parmenter's, and therefore a man of about his own age. He was a born mathematician and engineer, and, like many another before him, the dream of his life had been the conquest of the air by means of vessels which flew as a bird flew, that is to say by their own inherent strength, and without the aid of gas-bags or buoyancy chambers, which he, like all the disciples of Nadar, Jules Verne, Maxim and Langley, had looked upon as mere devices of quackery, or at the best, playthings of rich people, who usually paid for their amusement with their lives.

His father died soon after he left college, and left him a comfortable little estate on the north-western slopes of the Alleghanies, and a fortune in cash and securities of a million dollars. The estate gave him plenty to live upon comfortably, so he devoted his million to the realisation of his ideal. Ratliffe Parmenter, who only had a few hundred thousand dollars to begin with, laughed at him, but one day, after a long argument, just as a sort of sporting bet, he signed a bond to pay two million dollars for the first airship built by his friend that should fly in any direction, independently of the wind, and carry a dead weight of a ton in addition to a crew of four men.

Newson Hingeston registered the bond with all gravity, and deposited it at his bank, and then their life-ways parted. Parmenter plunged into the vortex of speculation, went under sometimes, but always came to the top again with a few more millions in his insatiable grasp, and these millions, after the manner of their kind, had made more millions, and these still more, until he gave up the task of measuring the gigantic pile and let it grow.

Meanwhile, his friend had spent the best twenty-five years of his life, all his fortune, and every dollar he could raise on his estate, in pursuit of the ideal which he had reached a few minutes later than the eleventh hour. Then he had sent that cable. Of course, he wanted the two millions, but what had so suddenly happened in England had instantly convinced him that he was now the possessor of an invention which many millions would not buy, and which might decide the fate of the world.

Within twelve hours of his arrival at his friend's house, Ratliffe Parmenter was entirely convinced that Newson Hingeston had been perfectly justified in calling him across the Atlantic, for the very good reason that he spent the greater part of the night taking flying leaps over the Alleghanies, nerve-shuddering dives through valleys and gorges, and vast, skimming flights over dim, half-visible plains and forests to the west, soaring and swooping, twisting and turning at incredible speeds, in fact, doing everything that any bird that ever flew could do.

When they got back to the house, just as dawn was breaking, and Mr Parmenter had shaken hands with Hiram Roker, a long, lean, slab-sided Yankee, who was Hingeston's head engineer and general manager, and had fought the grim fight through failure to success at his side for twenty years, he said to his friend:

"Newson, you've won, and I guess I'll take that bond up, and I'd like to do a bit more than that. You know what's happening over the other side. There's got to be an AËrial Navigation Trust formed right away, consisting of you, myself and Hiram there, and Max Henchell, my partner, and that syndicate has to have twenty of these craft of yours, bigger if possible, afloat inside three months. The syndicate will commence at once with a capital of fifty millions, and there'll be fifty more behind that if wanted."

"It's a great scheme," Hingeston replied slowly, "but I'm afraid the time's too short."

"Time!" exclaimed Mr Parmenter. "Who in thunder thinks about time when dollars begin to talk? You just let me have all your plans and sections, drawings and the rest of your fixings in time to catch the ten o'clock train to Pittsburg. I'll run up and talk the matter over with Henchell. We'll have fifty workshops turning out the different parts in a week, and you shall have a staff of trustworthy men that we own, body and soul, down here to assemble them, and we'll make the best of those chaps into the crews of the ships when we get them afloat.

"Now, don't talk back, Newson, that's fixed. I'm sleepy, and that trip has jerked my nerves up a bit. Give me a drink, and let's go to bed for two or three hours. You'll have a cheque for five millions before I start, and we shall then consider the Columbia our private yacht. We'll fly her around at night, and just raise Cain in the way of mysteries for the newspapers, but we won't give ourselves away altogether until the fleet's ready."

As they say on the other side of the Atlantic, what Ratliffe Parmenter said, went. He wielded the irresistible power of almost illimitable wealth, and during the twenty-five years that Hingeston had been working at his ideal, he and Maximilian Henchell, who was a descendant of one of the oldest Dutch families in America, and one of its shrewdest business men to boot, had built up an industrial organisation that was perhaps the most perfect of its kind even in the United States. It was run on lines of absolute despotism, but the despotism was at once intellectual and benevolent. To be a capable and faithful servant of Parmenter and Henchell, even in the humblest capacity, meant, not only good wages and provision for life, but prospects of advancement to the highest posts in the firm, and means of investing money which no outsider would ever hear of.

Wherefore those who worked for Parmenter and Henchell formed an industrial army, some fifty thousand strong, generalled, officered and disciplined to the highest point of efficiency, and faithful to the death. In fact, to be dismissed from any of their departments or workshops was financial death. It was like having a sort of commercial ticket-of-leave, and if such a man tried for work elsewhere, the answer was "If you can't work for P. and H. you must be a crook of some sort. I guess you're no good to us." And the end of that man was usually worse than his beginning.

This was the vast organisation which, when the word went forth from the headquarters at Pittsburg, devoted the best of its brains and skill to the creation of the AËrial Fleet, and, as Mr Parmenter had said, that Fleet was ready to take the air in the time he had allowed for its construction.

But the new ships had developed in the course of making. They were half as long again as the Columbia, and therefore nearly twice as big, with engines four times the power, and they carried three guns ahead and three astern, which were almost exact reproductions of those of the Ithuriel, the plans of which had been brought over by the Minnehaha on her second trip.

The Columbia had a speed of about one hundred miles an hour, but the new models were good for nearly a hundred and fifty. In appearance they were very like broad and shallow torpedo boats, with three aeroplanes on either side, not unlike those of the Flying Fishes, with three lifting fans under each. These could be driven vertically or horizontally, and so when the big twin fans at the stern had got up sufficient way to keep the ship afloat by the pressure under the aeroplanes the lifting fans could be converted into pulling fans, but this was only necessary when a very high speed was desired.

There was a signal mast and yard forward, and a flagstaff aft. The guns were worked under hoods, which protected the gunners from the rush of the wind, and just forward of the mast was an oval conning-tower, not unlike that of the Ithuriel, only, of course, unarmoured, from which everything connected with the working of the ship could be controlled by a single man.

Such is a brief description of the AËrial Fleet which rose from the slopes of the Alleghanies at ten o'clock on the night of the fourteenth of March 1910, and winged its way silently and without lights eastward across the invisible waters of the Atlantic.

There is one other point in Mr Parmenter's cablegram to Lennard which may as well be explained here. He had, of course, confided everything that he knew, not only about the war, but also about the approaching World Peril and the means that were being taken to combat it, to his partner on his first arrival in the States, and had also given him a copy of Lennard's calculations.

Instantly Mr Max Henchell's patriotic ambition was fired. Mr Lennard had mentioned that Tom Bowcock, Lennard's general manager, had proposed to christen the great gun the "Bolton Baby." He had spent that night in calculations of differences of latitude and longitude, time, angles of inclination of the axis of the orbit, points and times of orbital intersection worked out from the horizon of Pittsburg, and when he had finished he solemnly asked himself the momentous question: Why should this world-saving business be left to England alone? After all the "Bolton Baby" might miss fire by a second or two. If it was going to be a matter of comet-shooting, what had America done that she could not have a gun? Were there not hundreds of eligible shafts to be bought round Pittsburg? Yes, America should have that gun, if the last dollar he possessed or could raise by fair means or foul was to be thrown down the bore of it.

And so America had the gun, and therefore in after days the rival of the "Bolton Baby" came to be called the "Pittsburg Prattler."