Though it was nearing the first of November, the day, near land, was ideally soft and balmy. As many of the midshipmen as could sought the platform deck of the “Farnum.” Those, however, who belonged to the engineer division were obliged to spend the greater part of their time below.

By the time that the three craft were in the ordered formation, abreast, and well started down Chesapeake Bay, the parent vessel signaled that the designated cadets were to take charge of the handling of the submarine boats.

Jack Benson cheerfully relinquished the wheel to Cadet Midshipman Merriam, and stepped out on to the platform deck. At need, as in case of accident or misunderstanding of signals or orders, Benson was still in command. While all ran smoothly, however, Mr. Merriam enjoyed command.

Hal, being likewise relieved in the engine room, came also out on deck.

“Where's Eph?” inquired the young commander of the “Farnum.”

“Eph seems to have Truax on the brain,” laughed Jack.

“Well, Truax is a queer and surly one,” Hal admitted. “This morning he gives one the impression of peeking over his shoulder all the time to see whether he's being watched.”

“So Eph means to humor him by watching him, eh?” asked Jack.

Hal laughed quietly.

Some of the cadets who were familiar with the landmarks of Chesapeake Bay pointed out many of the localities and sights to the two submarine boys.

At last, however, Eph was obliged to call for Hal.

“You know, Hal, old fellow, I've got to look out for the feeding of a lot of boarders to-day,” complained Eph, whimsically.

This task of Eph's took time, though it was not a hard one. The food for the cadets had been sent aboard. Eph had to make coffee and heat soup. For the rest, cold food had to do. The young men, on this trip, were required to wait on themselves.

“Why don't you go on deck a while, Truax?” asked Hal, kindly.

“Don't want to,” snapped the fellow, irritably. So Hal turned his back on the man.

“Doesn't that part need loosening up a bit, sir?” asked the cadet in charge of the engineer division.

“Yes,” replied Hastings, after watching a moment; “it does.”

“I'll do it, then,” proposed Truax, roughly. He attempted to crowd his way past Hal, but the latter refused to be crowded, and stood his ground until the midshipman passed him a wrench. Then Hastings loosened up the part.

“You might let me do a little something,” growled Sam Truax, in a tone intentionally offensive.

“Don't forget, Truax, that I'm in command in this department,” retorted Hal, in a quieter tone than usual, though with a direct, steady look that made Sam Truax turn white with repressed wrath.

“You won't let me forget it, will you?” snarled the fellow.

“No; for I don't want you to forget it, and least of all on this cruise,” responded Hal Hastings.

“Silence!” ordered Hal, taking a step toward him.

Sam Truax opened his mouth to make some retort, then wisely changed his mind, dropping back into his former seat.

The noon meal was served to all hands. By the time it was well over the mouth of the Bay was in sight, the broad Atlantic rolling in beyond.

The sea, when reached, proved to be almost smooth. It was ideal weather for such a cruise.

Then straight East, for an hour they went, getting well out of the path of coasting vessels.

“Hullo! What in blazes does that mean?” suddenly demanded Hal, pointing astern at starboard.

The “Pollard” lay tossing gently on the water, making no headway. Hardly ten seconds later the “Hudson” signaled a halt.

Then followed some rapid signaling between the gunboat and the submarine that had stopped. There was some break in the “Pollard's” machinery, but the cause had not yet been determined.

“Blazes!” muttered Jack, uneasily. “It couldn't have happened at a worse time. This looks bad for our firm, Hal!”

Finally, a cutter put off from the “Hudson,” with a cadet midshipman in charge. The small boat came over alongside, and the midshipman called up:

“The lieutenant commander's compliments, and will Mr. Benson detail Mr. Hastings to go over to the 'Pollard' and assist?”

“My compliments to the lieutenant commander,” Jack replied. “And be good enough to report to him, please, that Mr. Hastings and I will both go.”

“My orders, sir, are to convey you to the 'Pollard' before reporting back to the parent vessel,” replied the midshipman.

The cutter came alongside, taking off the two submarine boys, while Eph Somers devoted himself to watching Sam Truax as a bloodhound might have hung to a trail.

Arrived on board the good, old, familiar “Pollard,” Jack and Hal hurried below.

“The machinery is too hot to handle, now, sir,” reported one of the naval machinists, “but it looks as though something was wrong right in there”—pointing.

After seeing this done, the two submarine boys left for the platform deck, for the engine room was both hot and crowded.

“How long is it going to take you, Mr. Hastings?” asked the naval officer in command of the “Pollard.”

“Half an hour to get the parts cool enough to examine, but I can't say, sir, how long the examination and repairs will take.”

So the officer in command signaled what proved to be vague and unsatisfactory information to Lieutenant Commander Mayhew.

“This is a bad time to have this sort of thing happen,” observed the naval officer in charge.

“A mighty bad time, sir,” Jack murmured.

“And the engines of the 'Pollard' were supposed to be in first-class condition.”

“They were in A-1 condition, when the boat was turned over to the Navy,” Jack responded.

“Do you imagine, then, Mr. Benson, that some of the naval machinists have been careless or incompetent?”

“Why, that would be a wild guess to make, sir, when one remembers what high rank your naval machinists take in their work,” Jack Benson replied.

Jack and Hal were both worried. The sudden break had a bad look for the Pollard boats, in the success of which these submarine boys were most vitally interested.

At last, from below, the suspected parts of the engine were reported to be cool enough for examination. The naval officer in charge followed Jack and Hal below.

Taking off his uniform blouse and rolling up his sleeves, Hal sailed in vigorously to locate the fault. Machinists and cadets stood about, passing him the tools he needed, and helping him when required.

At last, after disconnecting some parts, Hal drew out a long, slender brass piston.

As he held it up young Hastings's face went as white as chalk.

“Do you see this?” he demanded, hoarsely.

“Filed, crazily, and it also looks as though the inner end had been heated and tampered with,” gasped Jack Benson.

“This, sir,” complained Hal, turning around to face the naval officer in charge, “looks like a direct attempt to tamper with and damage the engine. Someone has done this deliberately, sir. It only remains to find the culprit.”

“Am I sure?” repeated Hal, all the soul of the young engineer swelling to the surface. “Take this piston, sir, and examine it. Could such a job have been done, unless by sheer design and intent?”

“Will the lieutenant permit me to speak?” asked the senior machinist, taking a step forward and saluting.

“Yes; go ahead.”

“Yesterday morning, sir,” continued the senior machinist, “we thought the engines needed some overhauling by someone more accustomed to them than we were. We saw one of the machinists of the 'Farnum,' sir, hanging about on shore. So we invited him aboard and asked him to look the engines over.”

“Describe the man,” begged Jack.

The senior machinist gave a description that instantly denoted Sam Truax as the man in question.

“Did you leave him alone in here, at any time?” demanded Hal.

“Let me see. Why, yes, sir. The man must have been alone in here some three-quarters of an hour.”

There seemed, now, very little need of carrying the investigation further.

“You think we're in running order, now?” asked that officer.

“If you give the speed-ahead signal, sir, I think you'll feel as though you had a live engine under your deck,” Hal assured him.

The signal was given, the “Pollard” immediately responding. She cut a wide circle, at good speed, returning to her former position, where the propellers were stopped.

“You suspect your own machinist, who was aboard?” asked the naval officer, in a low tone, of the submarine boys.

“If you'll pardon our not answering directly, sir,” Captain Jack replied, “we want to have more than suspicions before we make a very energetic report on this strange accident. But we shall not be asleep, sir, in the matter of finding out. Then we shall make a full report to Mr. Mayhew.”

“Success to you—and vigilance!” muttered the naval officer.

The gunboat's cutter came alongside, transferring Jack and Hal back to the “Farnum.”

Hal went directly below to the engine room.

“You fixed the trouble with the 'Pollard'?” demanded Eph Somers, eagerly.

“Yes,” Hal admitted.

“Why, I don't know as I'd want to commit myself in too offhand a way,” replied Hal, slowly, as though thinking.

“What appeared to be at the bottom of the trouble?”

“Why, it may have been that one of the naval machinists, not understanding our engines any too well, allowed one of the pistons to get overheated, and then resorted to filing,” Hal replied.

“What? Overheat a piston, and then try to correct it with a file?” cried young Somers, disgustedly. “The crazy blacksmith! He ought to be set to shoeing snails—that's all he's fit for.”

“It looks that way,” Hal assented, smiling.

Artful, clever Hal! He had carried it all off so coolly and naturally that Sam Truax, who had been closely studying Hastings's face from the background, was wholly deceived.

“This fellow, Hastings, isn't as smart as I had thought him,” muttered Truax, to himself.

The interrupted cruise now proceeded, the parent vessel signaling for a temporary speed of sixteen knots in order to make up for lost time.

Twenty minutes later came the signal from the “Hudson:”

Word was immediately passed below, and all the cadets of the engineer division came tumbling up.

To these, who had been in the engine room constantly for hours, the cool wind blowing across the deck was highly agreeable.

For the speed dash Captain Jack Benson had again taken command. He passed word below to Eph Somers to take the wheel in the conning tower.

Eph, therefore, came up with the last of the cadets from below. In the excitement of the pending race it had not been noticed by any of the submarine boys that Williamson was already on deck, aft. That left Sam Truax below in sole possession of the boat's engine quarters.

The gunboat now fell a little behind, leaving the two submarines some four hundred yards apart, but as nearly as possible on a line.

“Look at the crowd over on the 'Pollard's' decks,” muttered Hal. “They're all Navy folks over there.”

“And they mean to beat such plain 'dubs' as they must consider us,” laughed Captain Jack, in an undertone.

Suddenly the signal broke out from the gunboat.

“Race her, Eph!” shouted Captain Jack.

“Aye, aye, sir!”

Eph Somers's right hand caught at the speed signals beside the wheel. He called for all speed, the bell jangling merrily in the engine room.

A little cheer of excitement went up from the cadets aboard the “Farnum” as that craft shot ahead over the waters. The cadets were catching the thrill of what was virtually a race. At the same time, though, these midshipmen could not help feeling a good deal of interest in the success of the “Pollard,” which was manned wholly by representatives of the Navy.

In the first three minutes the “Farnum” stole gradually, though slowly, ahead of the “Pollard.” Then, to the disgust of all three of the submarine boys, the other craft was seen to be gaining. Before long the “Pollard” had the lead, and looked likely to increase it. Already gleeful cheers were rising from the all-Navy crowd on the deck of the other submarine.

From looking at the “Pollard” Captain Jack glanced down at the water. His own boat's bows seemed to be cutting the water at a fast gait. The young skipper, knowing what he knew about both boats, could not understand this losing to the other craft.

“The Navy men must know a few tricks with engines that we haven't guessed,” he observed, anxiously, to young Hastings.

“I don't know what it can be, then,” murmured Hal, uneasily. “There aren't so confusingly many parts to a six-cylinder gasoline motor. They aren't hard engines to run. More depends on the engine itself than on the engineer.”

“But look over there,” returned Captain Jack Benson. “You see the 'Pollard' taking the wind out of our teeth, don't you?”

“Yes,” Hal admitted, looking more puzzled.

“Do you think our engines are doing the top-notch of their best?” asked Benson.

“Yes; for Williamson is a crackerjack machinist. He knows our engines as well as any man alive could do.”

“Do you think it would do any good for you to go below, Hal?”

“What?”

“Williamson might get it into his head that I went below because I thought he was making a muddle of the speed. As a matter of fact, he knows every blessed thing I do about our motors, and Williamson is loyal to the core.”

“I know,” nodded Captain Jack. “I'd hate to hurt a fine fellow's feelings. Yet—confound it, I do want to win this burst of speed. It means, perhaps, the quick sale of this boat to the Navy. If we're beaten it means, to the Secretary of the Navy, that he already has our best boat, and he might not see the need of buying the 'Farnum' at all.”

“Give Williamson two or three minutes more,” begged Hal. “You might tell Eph, though, to repeat, and repeat, the signal for top speed. That'll show Williamson we're losing.”

Jack Benson walked to the conning tower, instructing Eph Somers in a low tone.

“I've signaled twice, since the first time,” Eph replied. “But here goes some more.”

“I wonder what's going wrong with our engines, then,” muttered Captain Jack, uneasily.

“It ain't in careless steering, anyway,” grumbled Eph. “I'm going as straight as a chalk line.”

He continued to look worried, for, by this time, the “Pollard” was at least a good two hundred and fifty yards to the good in the lead.

“I'm afraid,” muttered Hal, rejoining Benson, “that I'll simply have to go below.”

“I'm afraid so,” nodded Jack. “We simply can't afford to lose this or any other race to the 'Pollard.'”

“Williamson knows that fully as well as we do, though,” Hal Hastings went on. “And Williamson—”

Of a sudden Hal stopped short. He half staggered, clutching at a rail, while his eyes stared and his lips twitched.

“Why—why—there's Williamson—aft on the deck!” muttered Hastings.

“What!”

Jack, too, wheeled like a flash. Back there in a crowd of cadets stood the machinist upon whom the submarine boys were depending for the best showing that the “Farnum” could make.

“Williamson up here!” gasped Hal. “And—”

“That fellow, Truax, all alone with the motors!” hissed Captain Jack. Then, after a second or two of startled silence:

“Come on, Hal!”

Jack Benson stole below on tip-toe, though with the machinery running so much stealth was not necessary. Right behind him followed Hal.

As the two gained the doorway of the engine room Sam Truax had his back turned to them, and so did not note the sudden watchers.

There was a smile of malicious triumph on Truax's face as he turned a lever a little way over, thus decreasing the ignition power of the motors.

Both Jack and Hal could see that the gasoline flow had been turned on nearly to the full capacity. It was the poor ignition work that was making the motors respond so badly. A little less, and a little less, of the electric spark that burned the gasoline and air mixture—that was the secret of the gradually decreasing speed, while all the time it looked as though the “Farnum” was doing her level best to win the race.

Whistling, as he bent over, Sam Truax caught up a long, slender steel bar. With this he stepped forward, intent upon his next wicked step.

Sam Truax stood watching for his chance to thrust the steel bar in just where it would inflict the most damage. Then raising the bar quickly, he poised for the blow.

“Stop that, you infernal sneak!” roared Jack Benson, bounding into the engine room.

“Neither,” retorted Captain Jack, coolly. “I command here, and you know it. Put that bar down, and leave the engine room.”

“Come and take the bar from me—if you dare!” taunted the fellow, a more wicked gleam flashing in his eyes.

“Hal!” called Jack, sharply.

“Aye!”

“Call two or three of the cadets down here. Don't make any noise about it.”

This order was called without Benson's turning his head. He still stood facing the sneak while Hal sped away.

“Now, I've got you alone!” gloated Truax. “I'll finish you!”

A scornful smile curled Jack's lips as he gazed steadily back at his foe.

“Truax, you're a coward, as well as a sneak.”

“I am—eh?”

With another nasty oath Truax stepped quickly forward, the steel bar upraised.

He took but one step, however, for Captain Jack Benson had not retreated an inch.

Nor did Jack have his hands up in an attitude of guard.

“No.”

“Then you'll have to make good in a moment, for we're going to attack you.”

“Bah! I can stave in two or three heads before any number of you could stop me,” sneered the fellow, in an ugly voice.

“You could, but you won't dare.”

“I won't?”

“Not you!”

At that instant rapid steps were heard. Hal Hastings returned with three of the midshipmen, behind them Williamson trying to crowd his way into the scene.

“Just tell us what you want, Mr. Benson,” proposed Cadet Merriam, amiably.

“This fellow has been 'doping' our engines,” announced Captain Jack. “And now he's threatening to stand us off. We'll close in on him from both sides. If he tries to use that steel bar on any of us—”

“If he does, he'll curse his unlucky star,” declared Midshipman Merriam. “Come on, gentlemen. We'll show him some of the Navy football tactics!”

The three midshipmen approached Truax steadily from the right. Jack, Hal and Williamson stepped in on the left.

Having to watch both sides at once, however, he made a fizzle of it. The bar came down, but struck the floor.

Then, with a yell, the midshipmen leaped in on one side, Jack leading the submarine forces on the other. Mr. Merriam's trip and Jack's smashing blow with the fist brought Truax down to the floor in a heap.

“Now, cart this human rubbish out of here!” ordered Jack Benson, sternly. “Don't hit him—he isn't man enough to be worthy of a blow!”

Swooping down upon the prostrate one, Hal and the midshipmen seized Sam Truax by his arms and legs, carrying him bodily out of the engine room.

“Williamson,” commanded Captain Jack, “stop the speed.”

“In the race, sir. We—”

“Stop the speed,” repeated Benson.

“You're the captain,” admitted Williamson. Grasping the twin levers of the two motors he swung them backward.

“Disregard any signal to go ahead until we've had a chance to inspect the motors,” added Captain Jack.

Then the submarine skipper darted out into the cabin.

“Hold him please, until I can have the wretch taken care of,” requested Captain Jack, making for the spiral stairway to the conning tower.

Just as the young skipper stepped out on deck he heard the “Hudson's” bow-gun break out sharply in the halting signal.

Taking a megaphone, Benson stood at the rail until the gunboat ranged up alongside.

“Have you broken down?” came the hail from the gunboat's bridge.

“I thought it best to stop speed, sir. We'll have to look over our engines before it will be safe to attempt any more speed work,” Captain Jack answered. “I've caught a fellow tampering with our machinery. We hold him a prisoner, now. Can you take him off our hands, sir?”

“One of your own men?” came back the question.

“Of course, sir.”

“We'll send a marine guard to take him, on your complaint, Mr. Benson.”

“Thank you, sir.”

“You've had treachery aboard, have you?” asked the lieutenant commander, as he climbed up over the side.

“Rather. A new machinist, taken aboard just before we sailed from Dunhaven. The same fellow who must have played the trick on the 'Pollard's' engines yesterday,” Benson replied.

“I'll be glad to have a fellow like that in irons in the brig aboard the 'Hudson,' then,” muttered Mr. Mayhew. “I couldn't understand, Mr. Benson, how you were doing so badly in the full speed ahead dash.”

“The prisoner below is the answer, sir,” Captain Jack replied. He then led the corporal and two marines below. The corporal produced a pair of handcuffs, which he promptly snapped over Truax's wrists.

“You'll be sorry for this, one of these days,” threatened Truax, with a snarl that showed his teeth.

“Some day, then, if you please, when I have more leisure than I have now,” Jack retorted, dryly. “This man is all yours, corporal.”

“Coxswain, return for me after you've taken the prisoner to the 'Hudson,'” directed Mr. Mayhew. “Now, Mr. Benson, I would like to see what has been done to your engines.”

“That's just what I want to know, too,” responded Jack.

They found Hal and Williamson hard at work, inspecting the motors.

“The ignition power was lowered, and that may have been the most that the fellow did,” said Hal. “Yet, at the same time, before putting these engines to any severe test, I believe they ought to be cooled and looked over.”

Lieutenant Commander Mayhew frowned.

“These delays eat up our practice cruise time a whole lot,” he grumbled.

“I'll put the engines through their paces, and chance mischief having been done to them, if you wish, sir.”

“In the days to follow, sir,” put in Benson, earnestly, “I think we can more than make up for this delay. We won't have the traitor aboard after this.”

“What earthly object can the fellow have had for wanting to damage your motors?” demanded the naval officer, looking hopelessly puzzled.

“I can't even make a sane guess, sir,” Jack Benson admitted.

An hour and a half later the “Hudson” and the two submarines headed back for a safe little bay on the coast. Here the three craft anchored for the night.