The D-16 made the return journey very slowly, for the master hand of Lord Hastings was lacking and Frank, being no navigator and his knowledge of the lay of the land very poor, was forced to proceed cautiously. In Lord Hastings’ cabin, Jack was still busy dressing his commander’s wound.

He found, after an examination, that it was not as serious as he had at first feared. The long bladed knife had caught Lord Hastings on the left side, halfway between the waist and the shoulder, and, turning up, had opened a deep gash clear to the shoulder. Lord Hastings was very weak, for the wound had bled profusely, but he was in no danger.

Jack performed a creditable operation upon the wound, and after he had bandaged it carefully, Lord Hastings lay back and went quietly to sleep. Then Jack took command of the vessel.

It was early morning when Jack gave the signal to rise, for he wanted to be sure that he had passed all danger points before coming to the surface. When they did bob up from beneath the water, he found that he had gone too far by more than a mile. However, no harm was done, and the D-16 was quickly brought about and soon lay under the lee of the Queen Elizabeth.

Here she lay till midday when Jack went aboard to report. The commander was very anxious when he learned that Lord Hastings was wounded, but he accepted Jack’s report instead and announced that he would visit Lord Hastings some time during the day.

“Well,” said Frank to his commander as he sat at his side, “I guess this settles our Constantinople trip.”

“Why so?” asked Lord Hastings.

Frank was surprised.

“Why we can’t go with you in this condition,” he replied.

Lord Hastings smiled faintly.

“A little thing like this is not going to stop me,” he said. “True, I can do no fighting, but I can still navigate the boat.”

“But it is impossible,” said Frank.

“No, it is not impossible,” said Lord Hastings. “We shall go.”

At this moment Jack came in, and when he learned what Lord Hastings proposed to do, he attempted to dissuade him. So did the commander of the Queen Elizabeth when he came to visit Lord Hastings that afternoon.

But the commander of the D-16 was not to be dissuaded.

“I am the commander of this vessel,” he said grimly, “and when I give an order I want it obeyed. Mr. Templeton, you will get under way an hour after nightfall.”

Jack saluted. He said nothing, for he knew that to say anything would be useless. He had never seen his commander in just this frame of mind before, but he was smart enough to realize that Lord Hastings meant what he said.

Night fell. An hour later, in accordance with his orders, Jack gave the signal, and the D-16 sank slowly from sight.

Lord Hastings called Frank.

“Help me to my place at the periscope,” he said quietly.

“But, sir,” protested Frank.

“There are no buts,” said Lord Hastings. “Help me to my post.”

Frank said nothing further, but obeyed.

Seated in a chair beside the periscope, Lord Hastings took a long breath. Then he called to Jack.

“I’ll do the watching here,” he said. “You run the ship in response to my signals.”

Jack saluted.

Frank took the lookout, as usual, and once more the huge searchlight lighted up the water under the Dardanelles.

The time wore on, still all stood at their posts. Morning came and Lord Hastings said:

“According to my calculations we should now be in the Sea of Marmora. We will go up for a look about, Mr. Templeton.”

The D-16 rose until her periscope showed Lord Hastings the signs about her.

“Very good,” he said slowly. “You may go down to your previous depth.”

The D-16 sank again.

“See anything, sir?” asked Frank.

“Enough to know that my calculations were correct and that we are in the Sea of Marmora.”

“Any vessels in sight, sir?”

“Couple of merchantmen, as nearly as I could make out.”

“Did they see us, sir?”

“I think not. In fact I am sure of it.”

“That’s good, sir.”

“So it is. You may proceed at twenty-five knots.”

The D-16 gathered headway and soon was traveling along under the water at a great rate.

“Won’t we have to be careful of mines along here, sir?” asked Jack.

“I do not believe they have mined much as yet. They figure that there is little danger of the Allies forcing an entrance for some time to come. However, we may as well be careful. Take the lookout, Mr. Chadwick.”

Frank saluted and returned to his post.

“The only place we shall have to be really careful,” said Lord Hastings, “is when we near Constantinople. No matter how safe the Turks may have felt, it is hardly possible they have not taken all emergency precautions.”

“If not,” said Jack, “the German officers who have been put in charge of their forces will have done it for them.”

“I guess there is no doubt about that,” was the reply. “The Germans are thorough in everything they do.”

“Shall we land in Constantinople, sir?”

“I think not—unless it is necessary for some purpose that may arise later. Right now I see no need of landing.”

“There are sure to be Turkish warships there, sir?”

“I should think so, surely.”

“When do you reckon we shall reach there?”

“I had planned to enter the harbor about midnight.”

“Best time for such work, sir.”

“We’ll be aided by a moon tonight—or should be, at least.”

And it was midnight when the D-16, with her deck barely awash, drew into the harbor of Constantinople, slinking silently along, with every man at his post, seeking out her prey.

“Warship dead ahead,” called Lord Hastings, and gave the command to stop. “We couldn’t want a better place to launch a torpedo,” he added. “A miss at this distance is out of the question.”

The crew stood at attention, and action came swift and fast.

“Fire!” came the command at last.

A torpedo sped on its way.

Immediately the D-16 darted away to a safe place, and then arose to the surface to see the result of its work.

A half moon lighted up the scene about them, and Frank and Jack ascended to the bridge. Lord Hastings remained below.

Of a sudden a terrible din broke the stillness of the night. Hideous cries went up into the sky. Searchlights broke forth and swept the harbor. Aboard the Turkish warship, the victim of the submarine’s torpedo, confusion reigned. Officers tried in vain to restore some semblance of order among the crew until they could ascertain the extent of the damage done.

It was impossible. Never the coolest sailors in the world, the Turks lost whatever courage they may have possessed and a panic ensued aboard the wounded warship, which soon spread to other vessels in the harbor. There seemed to be no doubt in the mind of any as to the cause of the explosion.

“We’ll go down and try another one,” said Jack calmly.

They descended below, and a few moments later the D-16 was moving toward another victim. This ship and then a third were torpedoed with unerring aim, and the panic which followed above was terrible to behold.

In the city itself word of the disaster spread, and the Sultan and his cabinet, believing that the fall of the capital was imminent, hurriedly got together what papers of state they could lay their hands upon, and dashed in automobiles from the city.

“Well,” said Jack to Lord Hastings, “I guess we might as well call it a good night’s work and let it go at that.”

“I am of the same opinion,” replied his commander. “We must have created a terrible furore.”

“There is not much question about that,” said Frank with satisfaction. “I would like to go ashore and see what is going on.”

“I wouldn’t object to that either,” said Jack.

“It’s impossible,” declared Lord Hastings. “You would surely be captured.”

“I don’t think so,” said Jack. “In this confusion a boat could easily be launched and no one would be the wiser. Then, if you remained right here, we could return without trouble.”

“Besides,” interposed Frank, “we might be able to learn something of advantage.”

“What do you say, sir?” asked Jack.

Lord Hastings hesitated.

“I should say no, of course,” he replied at last, “but I find it hard to deny you boys anything. I suppose it could be done, if you exercised the proper precautions.”

“We will, sir,” broke in Frank. “Have no fear of that.”

“Nevertheless, it is just that that I am fearful of,” said Lord Hastings slowly. “You see, I know you of old.”

“Then we can’t go, sir?” asked Frank, greatly disappointed.

“I didn’t say that,” replied Lord Hastings.

“Then you mean we can, sir?”

“Well, yes, if you will give me your solemn promises to be very careful.”

“We will do that, sir, won’t we, Jack?”

“We will,” was his friend’s reply.

“In that event,” said Lord Hastings, “you have my permission to go. You will also promise to return within three hours.”

“We promise that also, sir,” said Jack.

“Then you may go; but if I were you I would remove your uniforms and don civilian clothes. Then you may pass muster anywhere, as there are many foreigners in the city.”

Jack and Frank heeded this advice, and hastened to their cabin to change their clothes.