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!"