side of the line the victors
gathered about their prey with a keenness which could come only of the
hope that they might find in it some suggestion that would make their
own flying more efficient. Each learned from the other, so that the
different schools on either side of the line had all the advantage of
watching the development of their rivals. Very shortly after an
improvement appeared on one side it reappeared in the planes of the
other side.

It is doubtful if ever a more desperate scientific battle was fought
than that which featured the development of the air services of the
various belligerents during the war. Control of the air was so vital
that neither could afford to overlook any possibility; and, as a
result, the scientific evolution was truly astounding. No man was
reserved on this subject of airplane improvement. All contributed
their best skill and ability to the common reservoir of knowledge.

Very soon man's conquest of the air became so complete that different
types of planes were developed for different kinds of work. The plane
of the early days which wandered off by itself wherever it saw fit,
gathered what information it could, and returned to drop a note to the
commander below, developed into a highly efficient two-seated plane
equipped with machine-guns for protection against attack, wireless for
sending back messages, and cameras for photographing the enemy's
positions below. The plane which had earlier dropped an occasional
bomb in a hit-or-miss fashion over the side now developed either into
a powerful two-seater with a great weight-carrying capacity and a
continually more efficient scientific method of aiming its missiles or
into a huge machine for long-distance night-bombing work capable of
carrying from two to a dozen men and from two to four tons of bombs.
During this time the strictly fighting plane, usually a single-seater,
increased in speed, "ceiling," and agility till it could dart, twist,
and dive about, three to five miles above the trenches, protecting
friendly bombing and observation planes below from enemy attack or
swooping down to send enemy planes in flames to the ground.

Vital though all this work was for the war, it had an incomparably
greater value for the perpetual struggle which all mankind is waging
against nature. While the various nations were seeking to destroy one
another through the air, they were in reality destroying the chains
which bound them to the ground