as yet impossible
to tell what the day might bring forth.

Then the last of the squadron arrived, and the signal was given to start
for the front. Away they went with a whirr and a roar, seven strong.
They overtook a number of clumsy two-seaters on the way, observation
planes, bombing machines, or it might be those included in the
"fire-control" units going to relieve some of their kind already doing
their appointed bit in the battle.

Tom looked far beyond. He could see great oceans of smoke arising that
told of innumerable high explosives bursting, and enormous guns being
discharged. Both sides seemed hard at work, though the French were
certainly sending ten shells to one that came from the forces of the
Crown Prince. This told plainly enough which army expected to do the
attacking that day.

And yet while all this wonderful panorama of war was spread beneath
them, the seven pilots moving onward in wild-geese formation, with the
captain at the head of the V, they heard nothing of the tumult raging.
In their muffled ears sounded only the loud whirr of the propellers, and
the deafening explosions of the engines. It was almost as noisy as a
boiler shop in full blast.

The fire-control planes were already sending back their signals, the
observer aboard intently following the course of each monster shell to
note exactly where it landed, and then communicating with the gunners,
so they might correct their faults and make each missile count.

German pilots were in the air also, sometimes in swarms. Theirs was the
task to attack these heavier machines and try to cripple or destroy
them.

Of course each one of these machines of the French "relage," or
fire-control, was armed with a quick-firing gun; and there was an
observer aboard, as well as a deft pilot. They carried such a large
assortment of material, consisting among other things of a complete
wireless outfit, that they had to be built with unusually large wings.

This makes them slow to answer to the call of the pilot; and when
attacked by the more nimble Fokkers they have a hard time to keep from
being shot down. That is why a number of the Nieuports with well known
"aces" in charge, must always be hovering over the fire controls, ready
to fly to their assistance in case they are attacked.

"Things are surely beginning to happen," murmured Tom. "The Boches seem
to be in an unusually fierce and aggressive humor on this particular
morning."

The youth was r