Below, Jack and Frank were still struggling with the German officer, but Lord Hastings had no time to lend them a hand. He raised his voice in a shout, and the crew came running at his command.

“Submerge instantly!” he cried.

But already sharp eyes aboard the German cruisers had caught sight of the submarine, and even as she sank suddenly from sight a single gun roared. The aim of this particular gunner was excellent; for the periscope of the D-16 was carried away as clean as a whistle.

Lord Hastings, who had been peering through it from below, was instantly aware of what had happened, and he immediately rushed to the compartment where the searchlight was placed and turned it on. This was now the only eye the submarine had with which to look for danger ahead.

Lord Hastings again raised his voice and a sailor came running to him. The commander of the vessel turned the lookout over to him and rushed to where he had left Frank and Jack.

When Frank had gone to his friend’s assistance, he had thought that together they would have little trouble overcoming the German officer. But the latter, in spite of Jack’s strength and all that Frank could do, was giving a good account of himself.

Blow after blow he landed upon each of the lads, but none had the power behind it to put them down. Time after time the two lads had closed in on him, only to be shaken off for the German was as slippery as an eel.

But finally Jack succeeded in gaining a strangle hold on the German, and putting forth his greatest strength, bore him to the floor, where both lads piled on top of him, pinioning his arms and legs. It was at this moment that Lord Hastings appeared upon the scene and rushed forward to lend a helping hand.

In falling the German’s head had come in violent contact with the floor, and he now lay still.

“Tie him up quickly,” commanded Lord Hastings. “We haven’t any time to waste on him.”

Jack and Frank hastened to obey, and soon the captive was securely bound.

The two lads noticed the signs of anxiety on their commander’s face and Frank asked:

“What’s the matter, sir?”

“Matter is that we are in a veritable nest of the enemy,” replied Lord Hastings. “Also our periscope has been shot away.”

“But we can rig up the other in no time,” said Jack.

“So we can,” said his commander, “but in the meantime they are likely to send a flotilla of submarines below to look for us.”

“Then we shall have to hustle,” said Frank.

“Hustle is the proper word,” agreed Lord Hastings. “Come with me.”

He led the way to the foot of the broken periscope, and quickly summoned several members of the crew. With all possible haste the second periscope, carried for just such an emergency, was brought out and run up.

“The only way we can tell whether it is adjusted properly,” said Lord Hastings, “is to rise, and that is exceedingly dangerous.”

“Well, we shall have to take a chance,” said Frank.

“So we shall,” was the reply. “You may give the order, Mr. Templeton.”

Jack did as commanded, and slowly the submarine began to rise. Lord Hastings stood at the foot of the second periscope, peering intently into it. At last he raised his hand in a sudden signal, and immediately the vessel began to sink again.

“It’s all right,” said the commander, turning to the lads. “I caught a glimpse of the surface.”

“Then we are all fixed again,” said Frank thankfully.

“Yes.”

“Then,” said Jack, “I should say the thing to do is to put as great distance as possible between us and the enemy.”

“The only draw back to that,” said Lord Hastings, “is that I do not know just where we are and to move in any direction is decidedly dangerous.”

“Weren’t you able to recognize the surroundings?” asked Frank.

“No; the canal is fortified all along, and all the fortifications look alike to me.”

“Well,” said Jack, “how about the prisoner? Don’t you think he can be made to pilot us out of danger?”

“No,” was the reply, “I don’t. I am absolutely positive he would refuse, no matter what the result. I am convinced that the only reason he agreed before was because he figured he could put us in the power of his friends. I don’t believe he scared worth a cent.”

“Nor I,” agreed Frank.

“Well, then what is to be done?” asked Jack.

“We shall just have to feel our way along carefully,” replied Lord Hastings. “But we must get away from this spot immediately. There is no telling what they may dump over on us. Straight ahead, Mr. Templeton, at seven knots.”

“Very good, sir,” replied the lad, and repeated the command to the engine room.

Lord Hastings himself took the helm, and Frank again stood watch in the forward compartment. For an hour they proceeded without incident, and then Lord Hastings decided to rise and take a look about.

Accordingly the pumps were set to work, and as the water was forced from the submersion tanks, the D-16 rose toward the surface. Lord Hastings, Frank and Jack ascended to the bridge.

“Well,” said the former, “we seem to have given them the slip.”

“It looks that way, sir,” replied Frank, after a quick glance over the water.

In the distance they could make out the forms of the battle cruisers, but evidently those aboard the German vessels did not perceive the submarine, lying low in the water.

Suddenly as the three stood talking, a figure bounded upon the bridge from below, and before any of the three could raise a hand to stop him, crossed the deck and hurled himself into the sea.

“Great Scott!” cried Frank. “It’s the German!”

“Impossible!” exclaimed Jack. “He was too securely bound to free himself.”

“But I am positive that is who it was,” said Frank.

All rushed to the side of the bridge, and peered intently into the water, waiting for the figure of the man to reappear upon the surface. Perhaps a minute later, they made out his form, quite a distance from the vessel, and swimming toward the distant German vessels with powerful strokes.

“Now I wonder how he managed to get——” began Jack, and paused suddenly.

For Frank, throwing off his coat, had hurled himself into the water and set out in pursuit of the fugitive.

“Here! Come back here!” called Jack to his friend.

Lord Hastings added his voice to Jack’s.

“Come back,” he cried. “Let him go.”

Frank waved one arm in the air and called back over his shoulder:

“I’ll get him. You wait right here for me if I am gone a year!”

Jack turned to Lord Hastings.

“Shall I jump over and bring him back?” he asked.

Lord Hastings shook his head.

“No,” he replied. “Let him go. If he can catch the German, all right; but I doubt it. However, when he finds that the chase is hopeless and that he is likely to fall into the hands of the enemy, he will turn back.”

“I’m not so sure about that,” said Jack. “Frank is rather hot headed at times, you know, and he is likely to chase him clear aboard a German warship.”

“I give him credit for more sense than that,” said Lord Hastings.

“So do I,” said Jack, “at times. At other times he loses his head altogether.”

“Well, the best thing we can do is to wait and see what happens,” said Lord Hastings. “The only thing that worries me is that the German may prove more than a match for him should he overtake him.”

“I’ll leave it to Frank to get himself out of any trouble like that,” said Jack. “The only thing that I am afraid of is his hot-headedness.”

In the meantime, exert himself as he would, Frank realized that he was not lessening the distance between himself and the fugitive; but the lad was not one to give up the chase so easily. He gritted his teeth and muttered to himself:

“I’ll get him if I have to chase him all around the world.”

After a time Frank’s hopes arose, for a quick look ahead showed him that he had gained a trifle. This encouraging sign lent strength to his arms. He struck out more vigorously than before, as he realized that it was only a question of time until he overtook his quarry.

But what the lad did not know was that at that very instant the lookout on the nearest German warship had caught sight of the two swimmers. A shouted command aboard the German vessel, and a launch put off over the side and dashed rapidly toward the German officer in the water.

This Frank did not see, and so swam on in ignorance of the danger that threatened. Raising his eyes, a couple of minutes later he saw the German officer as he was picked up by the boat, and for the first time realized that he was in a ticklish situation.

“Great Scott!” he muttered to himself. “Why didn’t I keep my eyes open? I hope they are satisfied with saving him and let me alone.”

He turned quickly, and made for the D-16 as fast as he could swim.

But his hopes were to prove fruitless, as a quick glance over his shoulder told him. In the launch he perceived the German commander gesticulating violently and pointing in his direction.

“I guess it’s up to me to hustle,” he told himself.

Now the German launch started after him, gaining at every stroke the lad made.

Lord Hastings and Jack perceived the turn of affairs, and Jack cried out:

“Get the launch over quick and man it. Unless we can lick these fellows, Frank is a goner.”

The crew acted with promptness, and in a twinkling the launch of the D-16 also was racing toward the swimming lad.