A MONSTER CANNON
Tom, dressing hastily, read the account in the Paris paper of the fall,
in an outlying section of the city, of one of the German shells that
failed to explode. It was being examined by the military authorities, it
was stated, with a view to finding out what sort of gun fired it, so
that measures might be taken to blow up the piece or render it useless
to the enemy.
"That sounds good to me," said Tom, as they made a hasty breakfast.
"This is getting down to a scientific basis. An unexploded shell ought
to give 'em a line on the kind of gun that fired it."
"The only trouble," said Jack, "is that the shell may go off when they
are examining it."
"Oh, trust the French ordnance experts not to let a thing like that
happen," said Tom. "Now let's go to it."
It was fortunate that Tom and Jack wore the uniforms that had so
endeared them to France, or they might have had difficulty in gaining
admittance to the bureau where the unexploded shell was under process
of investigation. But when they first applied, their request was
referred to a grizzled veteran who smiled kindly at them, patted them on
the shoulders, called them the saviors of France, and ushered them into
the ordnance department, where special deputies were in conference.
"Yes, we have one of the Boche shells," said an officer, who spoke
English fluently, for which Tom and Jack were glad. They could speak and
understand French, but in a case like this, where they wanted a detailed
and scientific explanation, their own tongue would better serve them.
"And can you tell from what sort of gun it comes?" asked Tom.
"It was fired from a monster cannon," was the answer. "That is a cannon
not so much a monster in bore, as in length and in its power to impel a
missile nearly eighty miles."
"Can it be done?" asked Jack.
"It has been done!" exclaimed Major de Trouville, the officer who was
detailed to talk to the boys "It has been done. That is the gun that has
been bombarding Paris."
"But, from a military standpoint," began Tom, "is it--"
"It is utterly useless," was the quick answer. "Come, I will show you
the shell."
He led them to an apartment set aside for the testing of explosives and
working out ordnance problems, and there on a table, around which sat
many prominent French officials, was the German shell--the "dud," as
Jack had called it.
"The charge has been drawn," explained Major de Trouville, "so there is
no danger. And we have determined that the manner in which shots reach
Paris from a distance of from seventy to eighty miles is by the use of a
sub-calibre missile."
"A sub-calibre?" murmured Tom.
"Yes. You know, in general, that the more powder you use, and the larger
the surface of the missile which receives it, the greater distance it
can be thrown, providing your angle of elevation is proper."
The boys understood this much, in theory at least.
"Well," went on the major, "while that is true, there is a limit to it.
That is to say you could go on using powder up to hundreds of pounds in
your cannon, but when you get to a certain point you have to so increase
the length of the gun, and the size of the breech to make it withstand
the terrific pressure of gases, that it is impracticable to go any
further. So, also, in the case of the shell. If you make it too large,
so as to get a big surface area for the gases of the burning powder to
act upon, you get your shell too heavy to handle.
"Now of course the lighter a missile is, the farther it will go, in
comparison to a heavy one with the same force behind it. But you can not
get lightness and sufficient resistance to pressure without size, and
here is where the sub-calibre comes in."
"In other words the Germans have been firing a shell within a shell,"
broke in another officer.
"Exactly," said Major de Trouville. "The Germans have evolved a big gun,
that is big as regards length, to enable the missile they fire from it
to gain enough impulse from the powder. But the missile would be too
large to travel all the way to Paris. So they use two. The inner one is
the one that really gets here and explodes."
"What becomes of the outer?" asked Jack.
"It is a sort of container, or collar, and falls off soon after the
shell leaves the big gun. If you will imagine a sort of bomb shell being
enclosed in an iron case, the whole being put in a gun and fired, you
will better get the idea. The outer case is made in two or more pieces,
and soon after it is shot out it falls away, leaving the smaller missile
to travel on. But here is where the cunning of the invention comes in.
The smaller missile has all the impetus given the larger one, but
without its weight. In consequence it can travel through eighty miles of
atmosphere, finally reaching Paris, where it explodes."
"Wonderful!" exclaimed Jack.
"And yet it is merely the adaptation of an old theory," went on the
major. "We have known of the sub-calibre theory for years, but it is not
practicable. So we did not try it. The cost is too great for the amount
of military damage done. And this shell, as you will see, is composed of
two parts, each with a separate explosive chamber, each containing, as
we discovered, a different sort of explosive. In this way if one did not
go off, the other would, and so set off the one that failed. It is very
clever, but we shall be more clever."
"That's right!" chimed in a chorus of fellow officers.
"We'll find the gun and destroy it--or all of them if they have more
than one, as they probably have," went on the major.
He showed the boys where the shell had chambers for the time fuses to
work, much as in a shrapnel shell, which can be set to go off so many
minutes or so many seconds after it reaches its objective point.
"And so the great question is settled by the failure of this shell to
explode," went on the major. "As soon as we saw it, and noted the
absence of the rifling groove marks, we knew it must have been a
sub-calibre matter. The rest was easy to figure out.
"Some of us thought there might be a big airship, stationed high above
the clouds, dropping bombs. Others inclined to the theory of a double
shell; that is, after one had been fired from the cannon it would
travel, say, half way and then explode a charge which would impel
another shell toward Paris. A sort of cannon within a cannon, so to
speak. But this is not so. Nor did the theory of a shell with a sort of
propeller device, like that of a torpedo, prove to be right. It is much
simpler--just sub-calibre work."
"And what is going to be done about it?" asked Tom. "I mean how can the
monster cannon be silenced?"
"Ah, that is a matter we are taking up now," was the answer of Major de
Trouville. "I fancy we shall have to call on you boys for a solution of
that problem."
"On us?" exclaimed Jack.
"Well, I mean on the aircraft service. It will be their task to search
out this great German cannon for us, to enable our gunners to destroy
it. Or it may be that it will have to be bombed from an aeroplane."
"That's the task I'd like all right!" cried Tom, with shining eyes.
"Same here!" echoed Jack. "Do you suppose we'll get a chance?" he asked
eagerly.
"You may," was the reply. "It may take all the resources of our airmen
to destroy this terror of the Germans. But it will be done, never fear!"
"_Vive la France!_" cried his companions, and there was a cheer in which
Tom and Jack joined.
And so a part of the secret was discovered. It was a monster cannon that
was devastating Paris. A great gun, the construction of which could only
be guessed at. But it must be destroyed! That was certain!