will include a small sector of the German trenches. Roughly
speaking this arc will extend from about Hamegicourt to Conde, both
within the German lines, I am sorry to say. Now then, somewhere in this
arc, or perhaps back of it, the German gun is placed. Anywhere else
where it would be possible for such a monster engine of war to be
erected, would bring it too close to our batteries.

"So that gives us the comparative location of the gun," went on the
French officer. "But the next question is not so easy to settle--how to
get rid of it. As I said, I think we shall have to depend on you
airmen."

"Well, we're for the job!" exclaimed Tom.

"I know you are. And it may fall to you, or to your friends. I will talk
of that later."

"Have you been able to get any idea of the kind of gun it is, or why it
fires at fifteen minute intervals?" asked Jack.

"We have been able to get no really reliable information save that which
we deduce by our observations of this shell and from what we know of the
location of our own and the German lines," the Major went on. "Up to now
our airmen have not been able to penetrate far enough without being
attacked, and such few as did get well over toward the Rhine could make
out nothing. I have no doubt the gun is well camouflaged."

"And is it true that it doesn't fire at night because the Germans are
afraid the flashes will be seen?" asked Tom.

"That may have been the reason at first, but they have fired at night,
of late, so they must have some way of concealing the flashes, or
perhaps setting off other flashes at the same time so as to confuse our
scouts."

"It's going to be some job," murmured Jack.

"You said something," agreed his chum.

They remained talking a little longer, and some of the officers who
knew the reason for Tom's visit to Paris, expressed regret that he had
no information as yet about his father.

"But take heart," one told him. "He is not dead, or we should have heard
of it. Of course he may have fallen into the hands of the Germans, and
then we would not know for some time."

"He may have been caught," agreed Tom. "While Tuessig is out of the game
on account of his injuries, he may be able to direct Potzfeldt, and that
scoundrel would have good reason for trying to get revenge on us."

"Ah, yes, I heard about your rescue of the young lady and her mother,"
said the major. "It was a brave deed."

"Oh, any one could have done it," said Tom, modestly.

"And