astings, "that for submarine warfare
there is nothing to equal the motorboat--particularly a swift motorboat
such as this; and we are now on our way to join the fleet."

"Fleet? Fleet of what?" asked Jack, with some sarcasm. "Fleet of
motorboats, perhaps?"

"Precisely," said Lord Hastings with a smile, and added: "You don't seem
to think much of the idea."

"No, I don't, sir," was the reply. "I was in hopes that we were to feel
a real vessel beneath our feet once more. What good is a motorboat
against a submarine, anyway?"

"That's what I would like to know," agreed Frank.

"I'll tell you," replied Lord Hastings. "But first let me ask you
something. Do you remember, the other day, of asking me to explain the
mystery of the vanishing submarines?"

"Yes, sir," replied both lads.

"Very well. The solution of this mystery is, primarily, motorboats."

"What do you mean, sir?" exclaimed Jack.

"Just what I say. In the main, the possible hundred German submarines
that have disappeared recently have been accounted for by high-speed,
powerfully armed motorboats. The government has discovered, after much
experimenting, that the one craft with an advantage over a submarine is
a powerful motorboat; and England now has a fleet of several hundred
scouring the seas in the proximity of the British Isles."

"But I can't see where they would do any good," said Jack.

"In the first place," said Lord Hastings, "they are so small that they
escape the notice of a submarine until the motorboat is almost upon
them; and then it is too late for them to act. Also, the motorboat,
being small, is a much more difficult object to hit with a torpedo--it
is, in fact, a very poor target. Then again, a motorboat is so much
swifter than a submarine that the advantage is all with the motorboat."

"By Jove, sir! the way you explain it I can see the advantages," said
Jack eagerly.

"And so can I," agreed Frank.

Lord Hastings smiled.

"You are easily convinced," he replied. "Had some of the admiralty
officials been convinced half so easily, this submarine menace might
have been effectually stopped long before this."

As the motorboat continued down the Thames, each occupant remained busy
with his thoughts. It was Frank who broke the silence.

"What has happened to the torpedoboat destroyers, sir?" he asked. "I
understood they were the real submarine foe, with their heavy nets."

"They are still in use," replied Lord Hastings. "You know