rfare of yours
is going to get a bit exciting."

"Yes," said Erskine, "I think it is. Halloa, Great Caesar! That must be
that infernal invention of Castellan's brother's; the thing he sold to
the Germans--the sweep!"

As he spoke a grey shape leapt up out of the water and began to circle
over the _Ithuriel_. He snatched the transmitter from the hooks, and
said, in quick, clear tones:

"Castellan--sink--quick, quick as you can."

The pumps of the _Ithuriel_ worked furiously the next moment. Lennard
held his breath as he saw the waves rise up over the decks.

"Full speed ahead again, and dive," said Erskine into the transmitter.
"Hold tight, Lennard."

The floor of the conning-tower took an angle of about sixty degrees, and
Lennard gripped the holdfasts, of which there were two on each wall of
the tower. He heard a rush of overwhelming waters--then came darkness.
The _Ithuriel_ rushed forward at her highest speed. Then something hit
the sea, and a quick succession of shocks sent a shudder through the
vessel.

"I thought so," said Erskine. "That's John Castellan's combined airship
and submarine right enough, and that was an aerial torpedo. If it had
hit us when we were above water, we should have been where those French
chaps are now. You're quite right, this sort of naval warfare is getting
rather exciting."

CHAPTER X

FIRST BLOWS FROM THE AIR

The _Flying Fish_, the prototype of the extraordinary craft which played
such a terrible part in the invasion of England, was a magnified
reproduction, with improvements which suggested themselves during
construction, of the model whose performances had so astonished the
Kaiser at Potsdam. She was shaped exactly like her namesake of the deep,
upon which, indeed, her inventor had modelled her. She was one hundred
and fifty feet long and twenty feet broad by twenty-five feet deep in
her widest part, which, as she was fish-shaped, was considerably forward
of her centre.

She was built of a newly-discovered compound, something like
papier-mache, as hard and rigid as steel, with only about one-tenth the
weight. Her engines were of the simplest description in spite of the
fact that they developed enormous power. They consisted merely of
cylinders into which, by an automatic mechanism, two drops of liquid
were brought every second. These liquids when joined produced a gas of
enormously expansive power, more than a hundred times that of steam,
which actuated the pi