Creeping stealthily forward beneath the water, the D-16 was advancing to the attack. Lord Hastings stood at the periscope and Jack was at his elbow. The vessel was prepared for action, and the crew stood at attention.

Lord Hastings touched Jack on the shoulder.

“Tell the watch to keep a sharp lookout for submarines,” he said. “The chances are that they have been thrown out in front of the battleships.”

Jack departed and gave the necessary order, after which he returned to his position.

It was just after dusk on the evening following the day on which Frank had been captured. All day and all during the previous night the D-16 had kept near the bottom, maneuvering first this way and then that, and not once had they caught sight of an enemy’s submarine, nor had they risen to the surface for a look about.

But now Lord Hastings had decided upon action. He had idled long enough. Therefore, after preparing for action, the D-16 had risen sufficiently to give her periscope free play, and the commander now gazed over the water.

“German battleship ahead,” he called to Jack. “Slow to five knots.”

The speed of the submarine slackened.

“Take the lookout yourself, Mr. Templeton,” was the next command.

Jack did as commanded, and peered intently ahead. In the dark murky water he could see but a few feet, for it had not been deemed advisable to turn on the searchlight and thus make a target for the enemy’s submarines.

However, the D-16 was progressing at a snail’s pace and could be halted upon the instant. Therefore, there was not much danger of encountering any obstacle, providing the man on lookout attended to his duties properly.

Suddenly a dark object loomed up ahead. Quick as a flash Jack signalled the engine room and the D-16 came to an abrupt stop. Jack reported to Lord Hastings.

“Dark object right ahead that looks like a submarine submerged,” he said calmly.

“Give the order to back away a hundred yards, then fire a torpedo into her,” was Lord Hastings’ command.

Slowly the D-16 backed away from the dark object ahead, and an instant later a sharp “click” gave evidence that a torpedo had been launched. Immediately Jack flashed on the searchlight.

While his eyes could not follow the flight of the torpedo, the huge and powerful searchlight showed him the result. Struck squarely amidships the German submarine, for such the object ahead proved to be, seemed to split wide open. The water poured in in a dense volume, and suddenly the enemy sank.

Jack shuddered.

“Must be a terrible death,” he muttered to himself. “However, if we had not sunk her she would probably have sunk us.”

Once more he reported to Lord Hastings.

“Way clear now, sir,” he said.

“Good,” was the reply. “Make your speed five knots and continue your course.”

Perhaps ten minutes more and then Lord Hastings gave the command to heave to. For, through the periscope, less than a quarter of a mile away, he could make out the form of a giant German battle cruiser, a trifle to starboard.

The electric signal board flashed its message of death:

“No. 5 torpedo!”

“Ready!”

“Fire!”

“Click!”

Just this little sound and then Lord Hastings gave the command to rise, for he wished to witness the effect of the torpedo on the German cruiser.

The D-16 rose swiftly, but not as swiftly as the torpedo had sped on its way. For when the submarine reached the surface the torpedo had already done its work, and the German cruiser was helpless. Men were jumping into the sea on all sides and swimming away.

Jack was struck with a sudden idea. He turned to Lord Hastings.

“If we could pick up one of those fellows,” he said, pointing, “perhaps we could find out what has happened to Frank.”

“Good,” replied Lord Hastings, “it shall be done.”

Upon his command the submarine forged ahead slowly directly toward the doomed German cruiser. Heads of men swimming began to bob up and down on both sides. Jack, leaning over the side, which was almost level with the water, suddenly stretched forth a hand and dragged a German petty officer aboard.

Frightened almost out of his wits, for he had not perceived the dark outline of the submarine, the German struggled fiercely; but he was no match for Jack, who soon subdued him.

The man was dragged below, and upon Jack’s request, the submarine was again submerged.

When the prisoner learned that he was aboard the British submarine he braced up, and when he found that he was not to be harmed, he proved willing to talk.

“Where is the English prisoner whom you captured yesterday?” Lord Hastings asked him.

“He has been sent ashore,” was the reply. “He was to have been taken to Berlin today, to be held as a prisoner of war; but I understand that for some reason it was put off till tomorrow.”

“I see,” said Lord Hastings, and as he did not wish to put the prisoner on his guard, he talked for some minutes of other matters.

“By the way,” he said finally, “how is our friend guarded? Is he locked in a cell, or what?”

“Yes,” was the reply. “He refused to give his parole, so naturally he had to be confined. However, he is perfectly comfortable and is being well cared for.”

“So he is locked up in the fort,” said Lord Hastings. “Then there is no chance of his being so foolish as to attempt to escape.”

“It certainly would be foolish,” said the prisoner, “although once outside the cell, he might lose himself for a while; but of course there would be no chance of his getting out of the country. You see, we are perfectly safe here, or were until you came along, so it is unnecessary to keep such a close watch.”

“And where is the fort where he is confined?” asked Lord Hastings.

“Only a short distance from the edge of the canal. It is called Fort Kaiserin.”

“Well,” said Lord Hastings as he turned away, having learned all that he desired to know, “I guess we had better get away from this spot or one of your submarines is liable to find us. Mr. Templeton, you may escort the prisoner to your own quarters and place a sailor on guard.”

Jack led the prisoner to his own cabin and, after stationing a sailor at the door, returned to Lord Hastings.

“What have you on your mind, sir?” he asked.

“What do you mean?” asked his commander.

“Why,” said Jack, “I know you were not asking all those questions for nothing.”

“That is true,” was the reply. “I was thinking that by donning German uniforms and going ashore, we might possibly rescue Frank.”

“I had thought of that myself, sir; and I believe it might be done.”

“So do I.”

“Then shall we make the attempt, sir?”

“Yes,” replied Lord Hastings, “we shall.”

“Good. When?”

“At once. We have no time to lose.”

“But the submarine. How shall we know where to find her?”

“I’ll fix that. Send Brennan to me.”

Jack departed and returned a moment later with Brennan, the chief engineer.

“Brennan,” said Lord Hastings, “Mr. Templeton and I are going to take the launch and go ashore. As soon as we have gone I want you to submerge just to the edge of the periscope and remain there until you see us returning. Then rise immediately to take us aboard, for we may come in a hurry.”

“But if an enemy should approach in the meantime, sir?” asked Brennan.

“In that case you will, of course, submerge at once, and then, making a detour, return to approximately the same spot. It may be necessary to take chances, but you will have to do that.”

“Very good, sir,” said Brennan, saluting.

Lord Hastings turned to Jack.

“We’ll go to the surface now,” he said. “We may as well start at once.”

Five minutes later, in the little launch, they were skimming over the water toward the shore, which they could just see in the darkness. They felt sure that they had quitted the submarine unobserved.

As soon as they were over the side, Brennan, in accordance with instructions, had immediately submerged.

Before leaving they had both attired themselves in German uniforms, and felt comparatively safe.

The run to shore took perhaps fifteen minutes.

When they at last set foot on land their first thought was for a hiding place for the launch. Several trees overhanging the canal at the point where they had landed afforded a slight shelter and into their shadow the launch was pulled.

“It’s the best we can do, and I guess she won’t be seen,” said Jack.

“At any rate we’ll have to take a chance,” replied Lord Hastings. “Now let’s go.”

They turned their faces westward, where, in the distance, they could make out the outlines of the German fortifications.

“How are we going to know which is Fort Kaiserin?” asked Jack.

“We’ll have to ask,” was the reply.

“Won’t that give us away?”

“I don’t think so. We can say we just came here.”

This plan was followed and a soldier directed them to the fort. They were just about to enter it and trust to luck, when their attention was attracted by the sound of a scuffle a short distance down the street.

“Let’s see what it is about,” said Jack. “It may help us in some way.”

Lord Hastings nodded his assent, and they dashed toward a struggling knot of men only a few yards away.