ss!" he stated presently. "I can see the
flash of that cannon. It seems to be pointed this way!"

"Let 'em shoot, they can't see anything but the periscope and they'd have
an awful time hitting that!" boasted Jimmie.

Scarcely had the lad spoken before the vessel was shaken by the force of
a mighty concussion. A gigantic wave tossed the craft up and forward with
a heave that threw the boys off their feet.

"What was that?" gasped Jimmie glancing at his companions with a
terrified face. "Has one of the fuel tanks blown up?"

"Nothing doing!" replied Harry. "I think that cannon hit the mine we just
passed. I'm glad we were no closer!"

"We'll soon be out of their range!" stated Jimmie. "Shut up your
periscope and we'll go deeper. Give us a little more speed, Harry!"

In an hour Jimmie declared that they should be out of sight of the island
altogether. The engines had been working at full speed ahead. Harry
nursed the machinery constantly, knowing that it was new and would,
therefore, require considerable care. Their urgent need for speed induced
the lads to crowd the machinery to the limit, and Harry was gratified to
note that every part responded properly to its task.

"Well, Mackinder," stated Ned as the tension on their nerves began to
relax with the increasing distance traveled, "we're surely grateful to
you for suggesting that we get away as you did!"

"My motive was largely a selfish one, I must confess," returned
Mackinder. "I wanted very badly to get away from that island."

"How did they ever get hold of you, anyhow?" questioned Jack.

"I left Amsterdam the same evening you did. After the Lena Knobloch went
past us as she did I knew there was little use trying to delay you.
Therefore, my aide and myself left at once on a train for Rotterdam.
There we found a fishing boat which we thought would answer our purpose.
We induced the captain to take us aboard, intending to cross to England.
After traveling some distance the storm overtook us. We were blown far
out of our course. The vessel was badly battered. The crew left in a
panic, leaving me on board. Just in time the German destroyer came along
and took me off. That's it in a nutshell."

"Yes, and then when you discovered us in our little boat you went and
told the captain of the destroyer a lot of nonsense, didn't you?"
questioned Jimmie in a somewhat aggressive manner. "Why did you do it?"

"I only told him that you had at one time a package that bel