resounding bass one.

"I'm not Andy; but I'll accept the invitation."

As the owner of the voice, a tall, well-set-up man with a military bearing, stepped into the room all the Scouts sprang erect at attention, and gave the Scout salute. Then they broke into three cheers.

"Why, Lieutenant Duvall, what are you doing here?" exclaimed Rob, coming forward.

The young officer shook hands warmly with the leader of the Boy Scouts. Then, while the others pressed closer to the lieutenant—the same officer who had conducted the aviation tests at the "tunnelled house"—he addressed Rob.

"The fact is, I came down here to see if you are willing to tackle some more adventures," he said.

"Are we—" began Rob; but a roar from the Scouts interrupted him.

"Just you try us, Lieutenant."

"More adventures? Great stuff!"

"I'm ready right now."

"You can count on me."

The air fairly bubbled with confusion and excitement.

The Lieutenant roared with laughter.

"I do believe if you boys were told to lead a forlorn hope up to a row of machine guns you'd do it," he exclaimed; "but all this time I've been leaving my friend outside. May I bring him in?"

"Why ask the question?" exclaimed Rob. "This room is at the disposal of the United States Army at any time."

"Well, in this case it must be at the disposal of the Navy also," smiled the officer. Then, turning his head, he called to someone outside in the hallway, "Dan, the Eagles are prepared to receive the Navy."

At the word, a stalwart young man of about Lieutenant Duvall's age, stepped into the room. He was deeply sun-burned, and had an alert, upright carriage that stamped him as belonging to Uncle Sam's service.

"Scouts of the Eagle Patrol," said Lieutenant Duvall, with becoming formality, "allow me to present to you Ensign Daniel Hargreaves, of the United States Navy, just now detailed on special service."

Once more came the Scout salute, and then, given with a will, the long drawn "Kr-e-e-ee" of the Eagles.

The naval officer's eyes twinkled.

"These are Eagles that can scream with a vengeance," he exclaimed to his companion.

"Yes; and they can show their talons on occasion, I can assure you," declared Lieutenant Duvall. "But 'heave ahead,' as you say in the Navy, Dan, and put your proposition before them."

The boys greeted this announcement with wide-open eyes. Somehow or other they felt impressed immediately that they were on the verge of another series of important adventures; that the unexpected visit of the officers had something to do with their immediate future. And in this they were not the least bit out of the way, as will be seen.

CHAPTER II.

THE FACE AT THE TRANSOM.

"Of course what I am going to say will be held strictly confidential?" began Ensign Hargreaves, looking about him at the bright, eager faces of the young Eagles.

"We are Boy Scouts, sir," responded Rob proudly.

"I beg your pardon; but what I am going to say is so important to the nation that one word of it breathed abroad might cause endless complications and the ruin of certain plans. I have come to see you because my friend, Lieutenant Duvall, told me that he did not know anywhere in the country of a band of boys of similar resourcefulness, courage and high training."

"That's going some," whispered Tubby, behind a plump hand, to Merritt Crawford.

"I said no more than they deserved, Dan," observed Lieutenant Duvall.

"So I should imagine from what you told me about the part they played in the matter of the biplane and the tunnelled house," responded the young officer. "I came to you for another reason, also," he went on reverting to the subject in hand; "I have heard that as well as being land scouts you are thoroughly at home on the water."

"Well," said Rob, "we've all of us been brought up here on the south shore. I guess we are all fair sailors and know something about sea-scouting as well as the land variety."

"It is mainly for that reason that I came to you," rejoined the naval officer. "For the mission which I am desirous to have you undertake a knowledge of sea conditions is essential."

"Gee! He's a long time coming to the point," mumbled Tubby impatiently.

"Have any of you boys ever heard of the 'Peacemaker submarine'?"

"So called because the nation possessing it would be so formidable as to insure naval peace with other countries?" exclaimed Rob quickly. "Yes, sir, I've heard of it."

"What has reached your ears about it?"

"Why, a week ago the papers said that a submarine of that type had been sold to Russia and shipped for that country from the factory of the inventor at Bridgeport, Connecticut," said Rob, with growing wonder as to what all this could be leading.

"Correct. But that submarine never reached Russia!"

"Did the ship that was carrying it sink?" asked Tubby innocently.

"No," smiled the ensign, amused at the fat boy's goggling eyes and intent expression; "the Long Island, the freighter conveying it, did not sink. Instead, it hung about the coast, and then, under cover of fog, slipped into the harbor of Snug Haven on the South Carolina coast. Snug Haven is a small place and a sleepy one. Under the blanket of fog the Long Island slipped in, as I have said. Then the submarine was hoisted overboard by means of a derrick, and under her own power run to anchorage off a small island not far from Snug Haven. The captain and crew of the Long Island were sworn to secrecy, and so far as we know not a soul, but those directly interested, is aware of the present location of the Peacemaker."

"But why, if the submarine was sold to Russia, was she not sent there?" inquired the mystified Rob.

"For the excellent reason that she was not sold to Russia at all," was the naval officer's rejoinder; "that was simply announced for the benefit of inquisitive newspapers who have been trying for a long time to get at the details of the 'Peacemaker submarine.' But it is not alone the newspapers we have had trouble with. Foreign spies, anxious to secure the Peacemaker for their governments, have harassed us at Bridgeport ever since the keel plates were laid."

"Then the United States has bought the submarine?" asked Merritt Crawford.

"Not yet. But the construction and principles of it are so efficient that Uncle Sam wishes to have first call on the craft."

"And you are going to test it at this lonely island in South Carolina?" cried Rob, guessing the truth.

"Perfectly right, my boy," was the response. "Off that little-frequented coast, beset with islands and shoals, we hope to carry out our tests unobserved. At Bridgeport this would have been an impossibility, and for that reason the story of the sale to Russia was concocted. Russia, I may add, was about the only country not represented by spy service at Bridgeport."

"And you say that nobody but the officials directly connected with the craft has any knowledge of its whereabouts?" asked Rob with deep interest.

"As far as it is humanly possible to be certain, such is our positive belief."

"But where do we fit into all this?" sputtered Tubby, acutely coming to the main point.

"I am coming to that," was the response. "From what I have told you, you will have gathered that no ordinary class of watchmen could be trusted to keep quiet about what is