Five minutes later and the D-16 was once more on her way, while behind her the ruins of a German submarine strewed the sea.

Immediately the D-16 had again submerged, Lord Hastings summoned Jack, Frank and the captured German officer to his quarters. Here, after motioning all to seats, he addressed the German commander.

“Captain,” he said quietly, “you are now aboard a British submarine that is about to attempt a passage of the Kiel canal.”

“What!” exclaimed the German officer, jumping to his feet. “It is impossible!”

“You are mistaken, sir,” replied Lord Hastings calmly. “With your help, I should say that it would be a matter of little moment.”

“With my help?” inquired the German officer.

“Exactly. You shall give us your assistance.”

“But, sir——” began the German.

Lord Hastings interrupted him with a wave of his hand.

“Protests will do no good,” he said quietly. “I take it that you are familiar with the locations of the mines and other danger points in and guarding the entrance to the canal. Am I right?”

The German officer bowed his head in assent.

“Then,” said Lord Hastings, “I fail to see why we should have much difficulty getting through.”

“You mean,” said the German slowly, “that you expect me to pilot your vessel through the canal?”

Lord Hastings bowed courteously.

“Exactly,” he replied.

The German officer drew himself up indignantly.

“That, sir,” he said, “is hardly a fair thing to ask of a prisoner.”

“Perhaps not, you being the prisoner,” replied the commander of the D-16. “Still, you may have heard that ‘All’s fair in love and war.’”

“And if I refuse?” said the German.

“Well, it’s hard to say,” replied Lord Hastings quietly. “But I can say this much: We cannot be burdened with any human excess.”

“You mean you will kill me?”

“Oh, no; nothing like that. Rather, I should suggest setting you adrift in a small boat.”

The German was silent for some moments, musing.

“And I might say,” continued Lord Hastings, “that you would be given no water or provisions.”

“You might just as well shoot me outright,” said the German.

Lord Hastings shrugged his shoulders.

“I couldn’t quite do that,” he replied.

“Well,” said the German officer, “if I must, I must, and that’s all there is about it.”

“I am glad you are so sensible,” said Lord Hastings. “Now, I shall turn the vessel over to you at once; but remember, at the first sign of treachery, there will always be a bullet waiting for you.”

The German bowed, but made no reply. Lord Hastings summoned a sailor, and instructed him to put the German officer in charge of the helm, but to keep close watch over him. The sailor and the German commander then left Lord Hastings’ quarters.

“Great Scott!” exclaimed Frank when they had gone. “Do you mean to tell me that you would have carried out your threat?”

“Well, hardly,” replied his commander with a laugh. “However, as you see, a threat in the proper place often works out advantageously.”

“Still,” said Jack, “I am not exactly satisfied that he means to play straight with us. He gave in too easily to suit me.”

“The same thought struck me,” declared Frank.

“Oh, I guess he’ll put us through,” said Lord Hastings.

“I’m not so sure,” from Frank skeptically.

“Well,” said Lord Hastings, “we’ll watch him carefully, and his first false step will be his last. We can’t afford to take chances now. One of us must be near him all the time.”

Thus it was arranged and Jack volunteered to take the first watch. Frank elected to take the second and Lord Hastings announced that he would take the third. This watch, it was agreed, would be maintained until they had passed through the canal.

Jack made his way at once to the helm, where he took up his station, while Frank and Lord Hastings turned in. Here the lad sat for four straight hours, not once relaxing his vigilance. Then Frank relieved him.

All went well in this second watch until there was but an hour of it left. Then the German commander turned to Frank.

“I’ll have to ask you to rise three fathoms,” he said.

“Rise?” said Frank. “What for?”

“Because,” was the reply, “the water is very shallow just ahead, and we shall run aground. We are now approaching the entrance to the canal.”

Frank looked at his captive long and searchingly. There was still a doubt of the German’s honesty of purpose in his mind, and for a moment he was undecided.

“We must rise at once,” said the German.

Frank made his decision quickly. “Very well,” he said quietly.

He stepped to the signal tube and gave the necessary order. A moment later the rising of the vessel became perceptible, as the water was slowly forced from her tanks.

Frank, not perfectly satisfied, however, stood facing the German officer, his hand on his revolver, determined to use it at the first sign of treachery.

But his uneasiness was without cause. When the submarine had risen the required distance, at a word from the German, her speed was increased and she moved forward again.

“Is there not danger of striking a mine up here?” asked Frank.

“There are a few about,” was the reply, “but I can guarantee that we shall not strike one. When the depth of the water permits, we shall go lower again.”

With this Frank was forced to be satisfied.

His four hours up, Frank was relieved by Lord Hastings, to whom he related what had occurred.

Lord Hastings listened quietly.

“I’m sure he will try no tricks,” he said. “However, I’ll keep an eye on him.”

“Still,” said Frank, “I have a premonition that all is not right.”

Lord Hastings laughed, and Frank retired.

Now the Kiel canal is not very long, sixty-one miles of water connecting the North and Baltic seas. It extends across the narrowest portion of Germany close to the boundary between Germany and Denmark, thus making a passage for German vessels from one sea to the other.

Lord Hastings had kept his own reckoning and believed, while he was not familiar with these waters, that he could determine when the Baltic end of the canal had been reached.

And, indeed, it seemed that he was right.

It was just after his watch, when Jack had relieved him and while he lingered in the compartment, that the German turned to Lord Hastings and said:

“You may rise now. You have done what it has been believed impossible for any hostile ship to do. You have passed through the Kiel canal.”

At that moment Frank, refreshed by a few hours’ sleep, entered.

As Lord Hastings was about to give the signal to rise, Frank stepped forward.

“One moment, sir,” he exclaimed. “Something tells me that all is not right. We had best be careful, sir.”

The German drew himself up.

“Do you mean to insinuate——” he began.

Jack silenced him with a word. Then he, too, turned to Lord Hastings.

“I can’t explain why, sir,” he said, “but I believe Frank is right. Also, you may remember, sir, how he has been right on more than one occasion and that you said hereafter you would place unusual confidence in his premonitions.”

“Bosh,” said Lord Hastings scornfully. “It is true I did say that, but this time there can be no mistake. I have kept the reckoning myself, and the German is right. By this time we should have reached the Baltic end of the canal.”

“But, sir,” protested Frank, “could he not have steered us the same distance, but in another direction? Is it not possible that when we come up we may be right in a nest of the enemy’s ships, or under the guns of their fortifications?”

“It is possible, yes,” replied Lord Hastings, “but you are wrong. You are both letting your imaginations run away with you. No; I am sure the man is up to no trick.”

“At least, sir,” protested Frank, “do not rise clear to the surface without looking about through the periscope.”

“That is good advice, and it shall be heeded,” said Lord Hastings. “Mr. Templeton, you may give the command to rise.”

Jack saluted and did as commanded, and with the periscope just above the water, the D-16 became stationary. Frank put his eye to the periscope and started back with an exclamation of dismay.

At the same moment the German officer sprang to the signal tube, and, in perfect English, gave the command to rise to the surface.

Jack took in the situation upon the instant and sprang toward the German even as he leaped toward the tube. But he was too late, and before he could countermand the order, the D-16 floated upon the surface of the water.

Jack, in the meantime, was grappling with the German officer, who had drawn a concealed revolver and was attempting to bring it to bear upon Lord Hastings. Frank sprang to his assistance, and Lord Hastings, unmindful of the struggle, and thinking only of the mistake he had made, stepped quickly from the compartment, and opening the conning tower, made his way to the bridge.

And there, he, too, started back in dismay, and no wonder. For what his eyes beheld was this:

Dead ahead rose the sheer walls of a massive fortress, the powerful guns of which swept the narrow canal for miles. And at either side, with the D-16 squarely between them, four battle cruisers rode gently on the waves.

Lord Hastings took one quick look at the flags that floated above the big battle cruisers, then dived hurriedly below.

For the flags that fluttered in the breeze were the flags of Germany!