On the first day of July, 1908, a scene which was destined to become historic took place in the great Lecture Theatre in the Imperial College at Potsdam. It was just a year and a few days after the swimming race between John Castellan and the Englishman in Clifden Bay.

There were four people present. The doors were locked and guarded by two sentries outside. The German Emperor, Count Herold von Steinitz, Chancellor of the Empire, Field-Marshal Count Friedrich von Moltke, grandson of the great Organiser of Victory, and John Castellan, were standing round a great glass tank, twenty-five feet long, and fifteen broad, supported on a series of trestles. The tank was filled with water up to within about six inches of the upper edge. The depth was ten feet. A dozen models of battleships, cruisers and torpedo craft were floating on the surface of the water. Five feet under the surface, a grey, fish-shaped craft with tail and fins, almost exactly resembling those of a flying fish, was darting about, now jumping forward like a cat pouncing on a bird, now drawing back, and then suddenly coming to a standstill. Another moment, it sank to the bottom, and lay there as if it had been a wreck. The next it darted up to the surface, cruised about in swift curves, turning in and out about the models, but touching none.

Every now and then John Castellan went to a little table in the corner of the room, on which there was a machine something like a typewriter, and touched two or three of the keys. There was no visible connection between them—the machine and the tank—but the little grey shape in the water responded instantly to the touch of every key.

"That, I hope, will be enough to prove to your Majesty that as submarine the Flying Fish is quite under control. Of course the real Flying Fish will be controlled inside, not from outside."

"There is no doubt about the control," said the Kaiser. "It is marvellous, and I think the Chancellor and the Field Marshal will agree with me in that."

"Wonderful," said the Chancellor.

"A miracle," said the Field Marshal, "if it can only be realised."

"There is no doubt about that, gentlemen," said Castellan, going back to the machine. "Which of the models would your Majesty like to see destroyed first?"

The Kaiser pointed to the model of a battleship which was a very good imitation of one of the most up-to-date British battleships.

"We will take that one first," he said.

Castellan smiled, and began to play the keys. The grey shape of the Flying Fish dropped to the bottom of the tank, rose, and seemed all at once to become endowed with human reason, or a likeness of it, which was so horrible that even the Kaiser and his two chiefs could hardly repress a shudder. It rose very slowly, circled among the floating models about two feet under the surface and then, like an animal smelling out its prey, it made a dart at the ship which the Kaiser had indicated, and struck it from underneath. They saw a green flash stream through the water, and the next moment the model had crumbled to pieces and sank.

"Donner-Wetter!" exclaimed the Chancellor, forgetting in his wonder that he was in the presence of His Majesty, "that is wonderful, horrible!"

"Can there be anything too horrible for the enemies of the Fatherland, Herr Kanztler," said the Kaiser, looking across the tank at him, with a glint in his eyes, which no man in Germany cares to see.

"I must ask pardon, your Majesty," replied the Chancellor. "I was astonished, indeed, almost frightened—frightened, if your Majesty will allow me to say so, for the sake of Humanity, if such an awful invention as that becomes realised."

"And what is your opinion, Field Marshal?" asked the Kaiser with a laugh.

"A most excellent invention, your Majesty, provided always that it belongs to the Fatherland."

"Exactly," said the Kaiser. "As that very intelligent American officer, Admiral Mahan, has told us, the sea-power is world-power, and there you have sea-power; but that is not the limit of the capabilities of Mr Castellan's invention, according to the specifications which I have read, and on the strength of which I have asked him to give us this demonstration of its powers. He calls it, as you know, the Flying Fish. So far you have seen it as a fish. Now, Mr Castellan, perhaps you will be kind enough to let us see it fly."

"With pleasure, your Majesty," replied the Irishman, "but, in case of accident, I must ask you and the Chancellor and the Field Marshal to stand against the wall by the door there. With your Majesty's permission, I am now going to destroy the rest of the fleet."

"The rest of the fleet!" exclaimed the Field Marshal. "It is impossible."

"We shall see, Feldherr!" laughed the Kaiser. "Meanwhile, suppose we come out of the danger zone."

The three greatest men in Germany, and perhaps on the Continent of Europe, lined up with their backs to the wall at the farther end of the room from the tank, and the Irishman sat down to his machine. The keys began to click rapidly, and they began to feel a tenseness in the air of the room. After a few seconds they would not have been surprised if they had seen a flash of lightning pass over their heads. The Flying Fish had sunk to the bottom of the tank, and backed into one of the corners. The keys of the machine clicked louder and faster. Her nose tilted upwards to an angle of about sixty degrees. The six-bladed propeller at her stem whirled round in the water like the flurry of a whale's fluke in its death agony. Her side-fins inclined upwards, and, like a flash, she leapt from the water, and began to circle round the room.

The Kaiser shut his teeth hard and watched. The Chancellor opened his mouth as if he was going to say something, and shut it again. The Field Marshal stroked his moustache slowly, and followed the strange shape fluttering about the room. It circled twice round the tank, and then crossed it. A sharp click came from the machine, something fell from the body of the Flying Fish into the tank. There was a dull sound of a smothered explosion. For a moment the very water itself seemed aflame, then it boiled up into a mass of seething foam. Every one of the models was overwhelmed and engulfed at the same moment. Castellan got up from the machine, caught the Flying Fish in his hand, as it dropped towards the water, took it to the Kaiser, and said:

"Is your Majesty convinced? It is quite harmless now."

"God's thunder, yes!" said the War Lord of Germany, taking hold of the model. "It is almost superhuman."

"Yes," said the Chancellor, "it is damnable!"

"I," said the Field Marshal, drily, "think it's admirable, always supposing that Mr Castellan is prepared to place this mysterious invention at the disposal of his Majesty."

"Yes," said the Kaiser, leaning with his back against the door, "that is, of course, the first proposition to be considered. What are your terms, Mr Castellan?"

Castellan looked at the three men all armed. The Chancellor and the Field Marshal wore their swords, and the Kaiser had a revolver in his hip pocket. The Chancellor and the Field Marshal straightened up as the Kaiser spoke, and their hands moved instinctively towards their sword hilts. The Kaiser looked at the model of the Flying Fish in his hand. His face was, as usual, like a mask. He saw nothing, thought of nothing. For the moment he was not a man: he was just the incarnation of an idea.

"Field Marshal, you are a soldier," said Castellan, "and I see that your hand has gone to your sword-hilt. Swords, of course, are the emblems of military rank, but there is no use for them now."

"What do you mean, sir?" exclaimed the Count, clapping his right hand on the hilt. After what he had seen he honestly believed that this Irishman was a wizard of science who ought not to be trusted in the same room with the Kaiser. Castellan went back to his machine and said:

"Draw your sword, sir, and see."

And then the keys began to click.

The Field Marshal's sword flashed out of the sheath. A second later the Chancellor's did the same, and the Kaiser's right hand went back towards his hip pocket.

Castellan got up and said:

"Your Majesty has a revolver. Be good enough, as you value your own safety, to unload it, and throw the cartridges out of the window."

"But why?" exclaimed the Kaiser, pulling a Mauser repeating pistol out of his hip-pocket. "Who are you, that you should give orders to me?"

"Only a man, your Majesty," replied Castellan, with a bow and a smile; "a man who could explode every cartridge in that pistol of yours at once before you had time to fire a shot. You have seen what has happened already."

William the Second had seen enough. He walked to one of the windows opening on the enclosed gardens, threw it open, dropped the pistol out, and said:

"Now, let us have the proof of what you say."

"In a moment, your Majesty," replied Castellan, going back to his machine, and beginning to work the keys rapidly. "I am here, an unarmed man; let their Excellencies, the Chancellor and the Field Marshal, attack me with their swords if they can. I am not joking. I am staking my life on the success or failure of this experiment."

"Does your Majesty consent?" said the Field Marshal, raising his sword.

"There could be no better test," replied the Kaiser. "Mr Castellan makes an experiment on which he stakes his life; we are making an experiment on which we stake the welfare of the German Empire, and, perhaps, the fate of the world. If he is willing, I am."

"And I am ready," replied Castellan, working the keys faster and faster as he spoke, and looking at the two swords as carelessly as if they had been a couple of walking sticks.

The sword points advanced towards him; the keys of the machine clicked faster and faster. The atmosphere of the room became tenser and tenser; the Kaiser leaned back against the door with his arms folded. When the points were within three feet of Castellan's head, the steel began to gleam with a bluish green light. The Chancellor and the Field Marshal stopped; they saw sparkles of blue flame running along the sword blades. Then came paralysis! the swords dropped from their hands, and they staggered back.

"Great God, this is too much," gasped the Chancellor. "The man is impregnable. It is too much, your Majesty. I fought through the war of '70 and '71, but I surrender to this; this is not human."

"I beg your pardon, Excellency," said Castellan, getting up from the machine, and picking the two swords from the floor, "it is quite human, only a little science that the majority of humanity does not happen to know. Your swords, gentlemen," and he presented the hilts to them.

"Bravo!" exclaimed the Kaiser, "well done! You have beaten the two best soldiers in the German Empire, and you have done it like a gentleman. But you are not altogether an Irishman, are you, Mr Castellan?"

"No, sir, I am a Spaniard as well. The earliest ancestor that I know commanded the Santiago, wrecked on Achill Island, when the Armada came south from the Pentland Firth. The rest of me is Irish. I need hardly say more. That is why I am here now."

The Kaiser looked at the Chancellor and the Field Marshal, and they looked back at him, and in a moment the situation—the crisis upon which the fate of the world might depend—was decided. It was not a time when men who are men talk. A few moments of silence passed; the four men looking at each other with eyes that had the destinies of nations in the brains behind them. Then the Kaiser took three swift strides towards Castellan, held out his hand, and said in a voice which had an unwonted note of respect in it:

"Sir, you have convinced me. Henceforth you are Director of the Naval and Military operations of the German Empire, subject, of course, to the conditions which will be arranged by myself and those who are entrusted with the tactical and strategical developments of such plan of campaign as I may decide to carry out on sea and land. And now, to put it rudely—brutally, if you like, your price?"

Castellan took the Kaiser's hand in a strong, nervous grip, and said:

"I shall not state my price in money, your Majesty. I am not working for money, but you will understand that I cannot convert what I have shown you to-day into the fighting reality. Only a nation can do that. It will cost ten millions of marks, at least, to—well, to so far develop this experiment that no fleet save your Majesty's shall sail the seas, and that no armies save yours shall without your consent march over the battlefields of the world's Armageddon."

"Make it twenty millions, fifty millions," laughed the Kaiser, "and it will be cheap at the price. What do you think, Herr Kantzler and Feldherr?"

"Under the present circumstances of the other monarchies of Europe, your Majesty," replied the Chancellor, "it would be cheap at a hundred millions, especially with reference to a certain fleet, which appears to be making the ocean its own country."

"Quite so," said the Field Marshal. "If what we have seen to-day can be realised it would not be necessary to pump out the North Sea in order to invade England."

"Or to get back again," laughed the Kaiser. "I think that is what your grandfather said, didn't he?"

"Yes, your Majesty. He found eight ways of getting into England, but he hadn't thought of one of getting out again."

Since the days of the Prophets no man had ever uttered more prophetic words than Friedrich Helmuth von Moltke spoke then, all unconsciously. But in the days to come they were fulfilled in such fashion that only one man in all the world had ever dreamed of, and that was the man who had beaten John Castellan by a yard in the swimming race for the rescue of that American girl from drowning.