utes the sea-plane's objective came in sight: a broad line
of railway crossing a canal by means of a steel bridge. It was evident
that the Germans meant this base to be a permanent one, for the bridge
was of massive construction, strong enough to bear the transport of the
heavy 42-centimetre guns, and yet sufficiently high above the waterway
to admit the passage of large lighters with towering deck-cargoes.

"Stand by!" cautioned the Flight-Sub. "Keep cool. Do as well as you
have already done, and everything will go like greased lightning."

Volplaning at an acute angle, the sea-plane swooped down upon her
quarry. Shrapnel shells burst over, in front, behind, and underneath
her. It seemed impossible that such a frail object could escape
destruction.

At five hundred feet the Flight-Sub checked her downward course.

"Now!" he ordered. "And again!"

Two puffs of white smoke marked the points of explosion of the powerful
bombs. One had fallen fifty yards short of the bridge; the other had
burst almost at the junction of the railway lines.

Round spun the sea-plane. As she turned Ross could discern the second
of the aerial raiders gliding down, while the third was still at a
great altitude. Before the one in which Ross was flying could again
soar over its target the second sea-plane had dropped three of her
missiles. All fell close to the bridge. The work of demolition was
accomplished, for when the smoke and dust cleared away the substantial
fabric had been precipitated, a mass of twisted steel, into the canal.

[Illustration: "THE WORK OF DEMOLITION WAS ACCOMPLISHED"]

"Two more on the station and then we've finished," exclaimed the
Flight-Sub. "Ready?"

"Ay, ay!" replied Ross.

He turned his head to watch the progress of the other sea-planes. One
was still maintaining a terrific altitude, and showed no signs of
making a volplane.

The other was nowhere to be seen. Perhaps it was as well that the
midshipman had not noticed what had befallen her, for a few seconds
previously a shrapnel shell had burst close underneath the chassis.
The explosion had communicated itself to the remaining bombs, with the
result that utter annihilation had overtaken the plucky British airmen
in the moment of their triumph.

Ross's companion had witnessed the catastrophe. More, his trained eye
had discerned half a dozen small specks in the western sky. Quickly he
brought his binoculars to bear upon them. No mistake