or so while things are simmering connected with that big affair. Of
course it's to be a great secret among the three of us; not another soul
knows anything about my project or the giant bombing plane I had shipped
over to France."

"That's understood, and we're as mum as a couple of clams," Jack told
him; and so they separated, little dreaming at the moment what a
remarkable series of circumstances were fated to arise that would bring
them together for the carrying out of an enterprise greater than
anything as yet recorded in the annals of aerial exploits.

Tom and Jack were back on the field before half an hour had elapsed,
making a fresh start for the clouds, just as eager as ever to have some
adventurous Hun airman accept their challenge and give them battle.

For a whole hour did they fly back and forth in the disputed territory
between the two armies. Far beneath they could see by the aid of the
powerful binoculars marching columns of soldiers, all heading toward the
northwest. These they knew to be the German forces, making one of their
regular daily retreats in fairly good order.

Behind them the Hun armies left innumerable nests of machine-gunners to
dispute the advance of the Yankee battalions, and hold them in check,
even at the price of utter annihilation. Many times the men selected for
this sacrifice to the Fatherland held grimly on until they were
completely wiped out by the sweep of the Americans.

Occasionally one of the Yankee pilots, provoked because none of the enemy
dared to accept the gauge of battle he flung before them, would swoop
down and try to make a target of these marching columns. Then for a brief