"I don't know," came Harry's hesitating reply. "I'll try!"

Accordingly the boy clambered from his position near the forward bulkhead to the compartment amidships, where the pumps were located. A shift of valves followed by a touch on the levers connecting the storage batteries with the electric pumps started the process of emptying the ballast tanks.

Almost instantly the forward end of the craft began to rise. Very shortly the deck was in a level position. Then, as Harry continued to empty the water ballast, Frank and Ned, a.s.sisted by Jimmie and Jack, threw the clutch on the propeller shaft out of contact in order to permit the tail shaft to turn without moving the engines.

They then endeavored to turn the portion of the shaft which projected through the stern bearing in the back up motion to free the propeller.

They hoped thus to release the rope which they believed to be wound around the outboard portion of the shaft.

Strive as they might, however, the shaft stubbornly refused to move.

Their utmost efforts were unavailing.

At length, out of breath and exhausted, Ned sank back upon a locker. He looked at his companions with a curious expression.

"What's the matter, Ned?" inquired Jack anxiously. "Are you ill?"

"I feel badly, boys," replied Ned. "Unless we can devise some means to free that line from the shaft, we are in a pretty tight fix!"

"How near the surface can you bring the boat, Harry?" asked Frank.

"The gauges show that we're about two and a half fathoms down at present," replied Harry. "I have pumped a lot more water out than would ordinarily be required to bring us to the surface."

"Then we must be held by that line!" declared Ned.

"Let's try some other maneuver with the ship before we give up!" put in Jack. "We're not half though our experiments yet!"

"All right, what'll you try?" asked Ned in a despairing tone.

"I don't know," was the answer. "But we're going to do something to help get us out of this fix. How would it do to fill the tanks to sink us as far as we can go? Then we could empty them in a hurry, which would make the boat rise swiftly. The jounce would perhaps break the line and let us up so we could get some fresh air."

"If we don't get some fresh air pretty soon, we'll have to do something desperate. The reserve tank is nearly exhausted!"

In compliance with Jack's suggestion, the ballast tanks were again filled. Gradually the "U-13" descended to the bottom. As the deck began to tilt forward, as it had done when the craft was first stopped, Harry threw into operation every pump that could be used to empty the water from the ballast tanks. The boat rose rapidly.

With a jerk that nearly threw the boys off their feet, the "U-13" came to a rest. The gauges still showed the same depth as before.

Ned's face turned ashen as he sank upon a locker. The others gathered around him, expressing sympathy. The boy was clearly distressed.

"Never mind, Ned!" spoke up Frank. "We're coming out all right! The only trouble is that we haven't tried the right thing yet!"

"But I can't seem to think of a thing to do in this case," protested the other. "I'm all out of ideas! I'm sorry that we tried to follow that other submarine. I wish we had taken Jimmie's advice!"

"Never mind that now, Ned. We're close to the surface. If it becomes necessary, I will volunteer to be shot out of the torpedo tube. I can rise to the surface, swim about until I get my wind again, and then dive and cut the rope. That will release the whole ship!"

"Jimmie, that's awfully good of you to offer that, but I feel that I should be the one to do it," was Ned's reply.

"No, sir!" declared Jimmie promptly. "You're in no condition to attempt anything like that. You're worried, and your heart action is not right just now. My mind is a blank, and my heart is as sound as a bullet! I'm just the one for the job!"

As if the matter were understood, Jimmie began divesting himself of his clothing. He deposited his jacket on the locker beside Ned.

"Harry," he said, turning to his chum, "will you see that the torpedo tube is connected up and in working order? You might try a discharge for practice. We can spare a little of this air!"

By the time Jimmie had stripped and secured a knife to a belt about his waist, Harry p.r.o.nounced the tube ready for operation.

"Now, fellows," said Jimmie, shaking hands with his chums, "there's about one chance in a million that I won't get through this all right. If you are not up to the surface in five minutes, you may know that I've failed.

Then you'd better send out another lad!"

"Me next!" shouted Jack, beginning to remove his shoes.

Harry was peering from the heavy gla.s.s protecting the forward porthole.

As Jimmie stepped forward to enter the torpedo tube, Harry held up a warning hand. He turned an anxious face to his friends.

"There's something outside here!" he announced in an anxious tone. "I saw it once, but didn't get a clear view!"

"What did it look like?" asked Jimmie. "Is it alive?"

"I'm not sure, but I think it's another submarine!"

"Probably the real 'U-13' come up to look us over. Never mind those fellows. I'm going ahead and cut this wagon loose!"

"Wait a minute!" cried Ned. "I see the craft over here to starboard. It's a peculiar vessel, too! I think I see a man!"

"I see him, too!" declared Frank from a porthole a short distance aft.

"Do you suppose he's trying to get us to descend again?"

"Maybe that's it! Let's try it, anyway!" offered Harry.

"Go ahead!" agreed Ned in a tone that showed he was again taking heart.

"Let's act on the suggestion. We can try our scheme later!"

Harry's hand had already found the levers. In a moment the ballast tanks were being filled with water. Gradually the vessel sank.

As the light grew more dim at the increased depth, Jimmie declared he could see the other vessel descending at about the same speed.

Presently the two craft were at the limit of their travel. The visitor rested on the deck of the Wanderer, while the 'U-13', in which the boys were imprisoned, hung again at an angle from the line.

Directly the lads saw the figure that had formerly attracted their attention. It was climbing the main shrouds of the wrecked ship. When the man reached a position level with their craft he began making signs and motions. In his hand he flourished a knife.

"Looks rather bad for us!" commented Jack.

"Don't you get him?" asked Jimmie impatiently. "He understands our predicament and intends to help us! He motioned out that he is going to climb the rigging until he can find the rope. Then he'll slide down it until he lands on our stern. If we'll agree not to start the engines while he's there, he'll cut the rope. But we must be ready at the ballast tanks to let the vessel settle slowly to the deck of the ship, so he can get off and clear the line from the propeller!"

"I don't believe it!" stated Jack. "I think he meant to cut the line as soon as he gets to it and let us settle down slowly. What would be the sense of his riding around the ocean seated on the stern of a disabled submarine? He's got too much sense for that!"

"Maybe you're right!" admitted Jimmie. "Let's float the boat on an even keel and see. I'm going to dress again!"

Even as the lad hastened to put on his clothes the boys felt a sudden dip made by the submarine. Gradually they descended.

"Hurrah, he did it!" exultantly cried Ned. "Now, where has he gone? I do hope he'll free the propeller wheel at once!"