he rudders has broken, sir," was the answer. "It's thrown us
off our even keel. I'll start the gyroscope, and that ought to
stabilize us."

"The gyroscope!" cried Tom. "I didn't bring it. I didn't think we'd
need it!"

For a moment Earle looked at his commander. Then he said:

"Well, perhaps we can make a shift if we can repair the broken rudder.
We must have struck a powerful cross current, or maybe a whirlpool,
that tore the main rudder loose. We've rammed a sand bank, or stuck her
nose into the bottom in some shallow place, I'm afraid. We can't go
ahead or back up."

"Do you mean we're stuck, as we were in the mud bank?" asked Mr.
Hardley.

"Yes," answered Tom, and Earle nodded to confirm that version of it.

"But we'll get out!" declared Tom. "This is only a slight accident. It
doesn't amount to anything, though I'm sorry now I didn't take my
father's advice and bring the gyroscope rudder along. It would have
acted automatically to have prevented this. Now, Mr. Earle, we'll see
what's to be done."

All night long they worked, but when morning came, as told by the
clocks, they were still in jeopardy.

And then a new peril confronted them!

Earle, coming from the crew's quarters, spoke to Tom quietly in the
main cabin.

"We'll have to turn on one of the auxiliary air tanks," he said. "We've
consumed more than the usual amount on account of the men working so
hard, and we used one of the compressed air motors to aid the
electrics. We'll have to open up the reserve tank."

"Very well, do so," ordered Tom.

But a grim look came to his face when Earle, returning a little later,
reported with blanched cheeks:

"The extra tank hasn't an atom of air in it, sir!"

"What do you mean?" asked Tom, in fear and alarm.

"I mean that the valve has been opened in some way--broken perhaps by
accident--and all the air we have is what's in the submarine now. Not
an atom in reserve, sir!"

"Whew!" whistled Tom, and then he stood up and began breathing quickly.

Already the atmosphere was beginning to be tainted, as it always
becomes in a closed place when no fresh oxygen can enter. Without more
fresh air the lives of all in the submarine were in imminent peril. And
even as Tom listened to the report of his officer, he and the others
began gasping for breath.

CHAPTER XVII

WHERE IS IT?

"Down on your faces!" called Tom to those with him in the cabin. "Lie
down, every one! The freshest air is near the