Lieutenant Stein entered the room.

"It's all right," he said. "Captain Von Cromp has given his consent. If you wish, I will conduct you up."

"Thanks," said Jack, and the two lads followed the officer.

Captain Von Cromp was on the bridge when the two boys emerged from below, and he walked over to them.

"I regret," he said, "that you should have had to witness what you have; but it is the fortune of war, you know."

"I have heard that before," said Frank dryly.

"Tell me, would you have blamed us had we put up a more stubborn fight below a while ago?"'

"No," was the reply. "I could blame you for nothing you did to an enemy in time of war and especially under such a stress of excitement."

Lieutenant Stein bade the boys good-night and went below. After some further talk, Captain Von Cromp followed him, and the boys were left alone on the submarine, save for the single man on look out.

Frank walked up to the latter and engaged him lit conversation.

A few moments later he turned Away, saying to the sailor that he and his friend "would take a turn or two about before going below."

Walking swiftly up to Jack, Frank said in a low voice:

"See if you can't find that small boat they used to pick us up."

"What--?" began Jack, but Frank interrupted him.

"Never mind the reason," he said. "Help me find it, that's all.

We'll have to hurry. Where do you suppose they put it?"

A few moments later they came upon the little craft, now above water, placed where the sea could not reach it when the submarine was submerged. Luckily it was out of view of the German on the bridge, and the two lads succeeded in unloosening it and getting it overboard without being seen.

Then Frank walked quickly back to the spot where the periscope protruded from below. Opening his coat he took the explosive out and, drawing a handkerchief from his pocket, tied it to the diminutive mine and hung the latter on the tube.

"Now for this German," he said to himself. "It wouldn't do for him to see that before I am ready."

He approached the man once more and asked several questions.

"Well," he said finally, "I guess I shall have to say good-night."

The German's reply was choked in his throat. Frank sprang forward, flung one arm around the man's, neck, and with the other clutched him by the throat, to prevent an outcry.

Then he freed one arm and struck out heavily. The German fell without a murmur. Frank ran across the deck to where he had left Jack.

"Into the boat quick!" he exclaimed.

Jack needed no further urging. Frank dropped lightly in after him, and soon they were rowing rapidly away.

"Give me that gun," said Frank after they had pulled some distance from the submarine.

"What are you going to do with it?" asked Jack.

"I'll show you," replied Frank grimly. "Give me the gun!"

Without another word Jack pa.s.sed the weapon to his friend.

"Now," said Frank, "lower yourself over the side of the boat and when I say dive, dive!"

"See here," said Jack, taking Frank by the arm. "Have you gone crazy? What do you think you are going to do?"

"I don't think anything about it," replied Frank, more quietly now. "I know what I am going to do."

"Well, what is it then? Out with it."

"Do you see that object hanging to the periscope tube on the submarine?" asked Frank.

"Yes, I see it. Why?"

"Don't you know what it is?"

"No; what is it?"

"Well, that's the little plaything I found in Lieutenant Stein's cabin. I'm going to bore a little hole through it with this gun you were kind enough to get for me."

"Good Heavens!" exclaimed Jack "You'll blow tip the submarine with all on board!"

"My idea exactly," replied Frank carefully.

"But--" protested Jack.

"The fortune of war, you know," said Frank, with some sarcasm.

"You heard Captain Von Cromp say he wouldn't blame us for anything we might do. Besides, they didn't give the poor fellows on that British battleship any warning, did they?"

"No," said Jack, "but--"

"Well, there are no buts here. You climb overboard and get ready to dive. When this bullet goes through that little plaything there will be an explosion that will kick up considerable excitement hereabouts. That's why I asked you if you couldn't get a rifle. We could have gone a little farther away then."

"Now see here," said Jack. "I guess those fellows have it coming to them. They don't deserve any better than they will get. As you say, 'the fortune of war.' I'm not kicking about that. What I want to know is if you can hit that thing."

"Hit it? Of course I can hit it. You dive when I say the word, and when you come up, if you do, come up, I'll guarantee you won't see any submarine."

"But how about you?" demanded Jack. "If I dive before you fire, how are you going to get away before the explosion?"

"I don't calculate I'll get away before it, but I'll be in the water the minute I fire. I won't wait to see whether I hit it or not. However, I'll drop the revolver in the boat, so in case I miss the first time, it will be dry enough to use again."

"But--" began Jack.

Frank stood up in the boat and pointed the revolver directly at the submarine.

"No more words," he said quietly. "Are you ready?"