be destroyed.

As a matter of fact, as was learned later, there were but two guns in
service at this time, one of the three having burst.[1]

[Footnote 1: While of course this story is fiction, the description
given above of the great guns and their method of firing and concealment
is strictly in accord with the facts, and made from a sight of aeroplane
photographs taken by the French, and from an official report, published
April 26, 1918, by Deputy Charles Leboucq of the Department of the
Seine.]

Even as the French squadron came hovering over the place where the
German monster guns were placed, the advance of Tom, Jack and their
comrades being disputed by the Huns, one of the super-guns was run out
to fire on its specially constructed platform.

That this should be done in the very faces of the French was probably
accounted for by the fact that the Germans were taken by surprise. It
took some little time to arrange for firing one of the big cannons, and
it was probably too late, after the French airmen were hovering above
it, to get word to the crew not to discharge it.

As it happened, Tom and Jack, with Boughton, who had kept pace with
them, witnessed the firing of the big gun. As it was discharged, ten
other heavy guns, but, of course, of much less range, were fired off,
being discharged as one to cover the report of the giant mortar. And at
the same time dense clouds of smoke were sent up from surrounding hills,
in an endeavor to screen the big gun from aeroplane observation. But it
was too late.

In another moment, and even as the echoes of the reports of the ten
cannons and the big gun were rumbling, the bombing machine of the French
came up and began to drop explosives on the spot. At the same time word
of the location of the great cannon was wirelessed back to the camp, and
there began a devastating fire on the guns that had been, and were even
then, bombarding Paris.

CHAPTER XXII

OVER THE RHINE

It was a battle of the air and on the ground at the same time. From
above the French, American and British airmen were dropping tons of
explosives on the emplacements of the big guns and on the railway spurs
that brought them to the firing points. It might seem an easy matter for
an airship flying over a place to drop an explosive bomb on it and
destroy it. But, on the contrary, it is very difficult.

The bombing plane must be constantly on the move, and it takes a pretty
good eye to calculate t