"Probably a shark come to finish us up quickly," he replied
calmly.

Both lads, with a last effort, swam desperately from the place.

But suddenly the waters of the North Sea parted, and a long,
cigar-shaped object came to the top and rested lightly on the
water.

"What is it?" asked Jack again in no little alarm

Before Frank could reply, a man suddenly appeared on the top of
the object, apparently from nowhere, and glanced about. He
espied them, and as suddenly disappeared. He reappeared almost
in an instant, however, followed by another.

And now both lads discovered what the object was, an object that
had arrived just in time to save them from a watery grave. They
could see that the two men wore the uniform of the German navy.

The long, cigar-shaped object was a German submarine.





CHAPTER IV

ABOARD THE X-9