Thrilled by the nature of the communication made by the British officer, Frank, Billy and Pudge stood there staring at one another.

Of course it was not so very difficult for Frank to understand just why this invitation to accompany the raiding party of British aviators had come to them. Back of it all was the French Government, he felt certain. Before going into the business of making heavy investments connected with the new American seaplane patents it was only natural they should desire to witness an efficient test of the machine’s superiority over any aëroplanes they already possessed.

The contemplated raid would afford such a test. Competent critics, those other experienced birdmen, would be near to gauge the capacity of the Sea Eagle. In other words, the French Government did not want to “buy a pig in the poke.” Unless the hybrid sea and aircraft could meet the requirements laid down, they would not dare risk squandering great amounts of money in those hard times to duplicate her model.

Frank was greatly pleased. It seemed as though he and his chums had received a magnificent compliment in being honored with such an invitation.

“Of course, Major Nixon, you have been authorized to see us, and extend this courtesy?” he asked, as a starter.

“I can show you my credentials in that line, Frank,” the genial officer replied, without the least hesitation or embarrassment, which he accordingly proceeded to do, thus relieving the other’s mind in the beginning.

“Everything is shipshape, sir,” said Frank. “Now let us talk about the conditions under which we are to be allowed to accompany the expedition”

“Please keep your voice lowered as much as you can while I instruct you,” begged Major Nixon.

“You are thinking of those German spies who are said to be everywhere?” ventured Frank, who had heard much talk along these lines ever since arriving at Dunkirk.

Indeed, the stories that passed current concerning spies were astonishing. Most of them Frank did not believe in at all, for he knew they were founded on the fears of the people. At the same time the secret agents of the Kaiser were certainly vigilant as well as bold, and if one had to err at all it were better to be on the safe side.

“In times past I haven’t taken much stock in the wild stories that have been going around,” said the soldier, smiling; “but we certainly know there are spies in Dunkirk at this very hour. In fact, you boys have had pretty strong evidence that your operations while here have been watched day by day.”

“Yes,” remarked Billy, “and after what happened last night we are ready to believe almost anything, sir. I remember reading that sometimes the walls have ears, and I guess it may be so.”

“Under such conditions then it is best that we get our heads close together and talk in very low tones,” said the officer. “There are guards posted all around the stockade now, and yet in spite of that precaution some of those German spies are smart enough to play the game.”

“Anchors and aëroplanes, but this is exciting enough to please even a fellow built like you are, Billy!” muttered Pudge, who was mopping his red forehead with his handkerchief, though the others did not consider it any too warm there in the hangar of the great seaplane.

“I am unable to tell you at this minute the exact hour when the start will be made,” Major Nixon whispered. “Much depends on the state of the weather, and the arrival of the fleet of aëroplanes from across the Channel, for most of them will come from England, you understand.”

“Conditions being favorable, then,” observed Frank, “you believe that by another morning the start of the raiding party will take place?”

“Yes, undoubtedly,” came the answer. “We wish to take advantage of the unusually good weather conditions. Then, besides, we have learned through certain sources of information that the Germans on their own hook are planning an extensive dash with their aëroplanes and dirigibles on the coast cities on the Channel. It is in hopes of balking that, as well as accomplishing other results that more than thirty seaplanes will make this stupendous raid on their submarine bases at Ostend, Zeebrugge and Blankenberghe.”

“Sandwiches and sauerkraut!” Pudge was heard to gasp, as though his breath were almost taken away by the magnitude of this assertion; for he had never as yet seen as many as thirty aëroplanes assembled together, and certainly not in action.

“Is that the only motive of the raid, Major Nixon?” Frank asked, for he invariably made it a point to acquire all the information possible.

“Well,” continued the soldier, “to be perfectly frank with you, there are a number of other objects which such a sudden attack is likely to influence. It is aimed to destroy the railway station at Ostend so as to greatly hinder the movement of troop trains and those carrying ammunition and supplies. Then, at Bruges, other damage may be done.”

“But isn’t there still another big object in it?” insisted Frank.

“I suppose you are referring to the great submarine blockade of the coasts of Great Britain which Germany proposes to inaugurate next week?” said Major Nixon. “Yes, although I have not been so informed, I can guess readily enough that by means of this raid it is hoped to extensively damage their submarine base at Zeebrugge, and injure the movement in the beginning.”

“In other words,” said Frank, “Great Britain means to throw down the gage of battle, and warn Germany she can make just as dashing raids as anyone. No one nation is mistress of the air in this world war—as yet.”

Major Nixon smiled as he heard those last two words, and saw the quick look of pride which the young aviator threw toward the monster seaplane that was housed in that hangar.

“It’s plain that you have the utmost confidence in the ability of your machine to wrest that supremacy from the Germans, if once France secures the right to manufacture a fleet of Sea Eagles,” he remarked, as he laid a hand upon the shoulder of Frank Chester, of whom the bluff soldier had become quite fond in the short time they had known each other.

“Then it is understood, Major, that we keep ourselves in readiness to start out so as to be on the move at dawn, for I don’t imagine such a great fleet of aëroplanes would wish to make a start in the darkness of night.”

“No, there is no necessity of such a thing,” came the quick reply. “In fact, one of the objects of this raid is publicity. We do not aim to creep up and damage the enemy in the dark. We want him to see the astonishing sight of such a mass of darting seaplanes descending on his coast towns like a flock of eagles, and destroying military property, not citizens’ private homes, mind you.”

“I think,” said Frank, “I can speak for my friends here as well as myself, Major, when I promise to be ready for the signal. How will we know when to start out, for we shall all sleep here to-night?”

“There is only one condition which you will be asked to meet,” said the other.

“Then tell us what it is, sir.”

“The French Government will expect to have a representative aboard the Sea Eagle during the flight, not to interfere in the slightest degree with your mastery of the seaplane, but simply to take notes concerning her behavior under every sort of condition.”

“We certainly agree to that condition, Major Nixon,” said Frank heartily. “In fact, I should have asked that one be sent out with us. It is a part of our policy to fully satisfy the authorities we’ve been dealing with for nearly a year, now, that everything we claim, and much more, is possible with our advanced model of a hydro-aëroplane.”

“Very good, and I am pleased to know it,” said the officer. “I shall have to go back to town, now, but I will advise the local representative of the Government that you accept the conditions. By early dawn there will appear here a skillful aviator with written credentials, and I hope his ultimate report will be all you boys hoped it to be. My word! I only wish I were going with you, but other duties must claim my attention.”

He shook each one of them warmly by the hand.

“The best of luck, Frank,” were his last words at parting. “I trust that you may have an experience calculated to dwarf anything that has ever come your way.”

Frank, as he contemplated what a thrilling adventure lay before them, fancied that this wish on the part of Major Nixon was in a fair way of coming true. It certainly would be difficult to imagine a more exciting experience than taking part in an aërial raid, where more than thirty seaplanes started out to bombard strongly fortified coast defenses of the enemy, each raider subjected to a continual fire from every known species of anti-aircraft gun known to modern warfare.

After the soldier had left them, the three Boy Aviators sat around and talked in low tones. They had barred the door, and so far as they could see there was not the slightest chance that any eavesdropper could get close enough to overhear what they said. Nevertheless, the caution of Major Nixon had its effect upon them and there was no loud conversation except when ordinary matters were touched upon.

Frank always liked to “potter” around and give little touches of improvement to some part of the seaplane in which he had such a deep interest. No one knew its good and bad qualities as well as Frank; even its inventor had not studied these points as carefully as the young aviator.

So it happened that from time to time the boy made numerous little improvements that he figured would cause the motors to work more smoothly, or strengthen some part of the framework that showed signs of weakness.

Half a dozen times Frank left his two chums, sitting there killing time, to attend to something connected with the plane. He had carefully examined to find what had caused the accident that gave them such a thrill when thousands of feet above the earth.

“The same thing will never occur again, that I’m as sure of as I am of my own name,” he told Billy, when the other asked him about it.

Several hours had passed since the soldier had left them. Pudge, having taken a stroll outside, came back to report that there were at least a dozen British “Tommies” standing guard around the enclosure in which the hangar had been erected.

“It’s a good thing, too,” said Pudge, “because a crowd has come out from town to hang around here in hopes we’ll make a flight to-day. Oilskins and onions, but I should think there must be a hundred people if there’s one. But those Tommies are ready to use their bayonets on the first fellow who tried to climb up and peep over the stockade.”

“There are two guards, I noticed, down by the end of the trestle, where it strikes the water,” observed Billy, who had been moving around.

Frank was doing some little job under the seaplane, and at this moment came sauntering toward his two mates. Billy, happening to glance up at the other’s face was surprised to see that Frank looked excited; at least his eyes sparkled strangely, and there was a grimness in the way he had set his jaws.

Billy, always inclined to be explosive, might have burst out with a question only that he received a quick and expressive look from Frank, accompanied by the placing of a finger on his lips. Then, as Frank dropped into a chair beside them, Billy leaned over to whisper:

“What’s up now, Frank, that you’re looking so mysterious?”

“I’ve just made a discovery, that’s all,” came the same sort of careful reply. “Fact is, after all our precautions we’ve been outwitted, for there’s a spy hidden in the hangar right now!”