s of the
Section Photographique or in a dark room on wheels. If the first
examination of the negative reveals anything of interest, it is at
once enlarged, often to eight times the size of the original. As a
result of this remarkable system of aerial espionage, there is nothing
of importance which the Germans can long conceal from the Allies. They
cannot extend their trench lines by so much as a yard, they cannot
construct new positions, they cannot mount a machine-gun without the
fact being registered by those eyes which, from dawn to dark, peer
down at them from the clouds. At all of the divisional headquarters
are large plans of the opposing enemy trenches, which are corrected
daily by means of these airplane photographs and by the information
collected through the elaborate system of espionage which the Allies
maintain behind the German lines. To deceive the aerial observers,
each side resorts to all manner of ingenious tricks. To suggest an
impending retirement, columns of men are marched down the roads which
lead to the rear; trenches which are not intended to be used are dug;
and there are, of course, hundreds of dummy guns, some of which
actually fire. The officer in command of the Belgian Photographic
Section had heard that I was in Dunkirk in May, 1915, when it was
shelled by a German naval gun, at a range of twenty-three and one-half
miles.[G] So he gave me as a souvenir of the experience a photograph,
taken from the air, of the gun emplacement after it had been
discovered and bombed by the Allied aviators, and the gun removed to a
place of safety. I reproduce the photograph herewith. The numerous
white spots all about the emplacement are the craters caused by the
bombs which were rained upon it.

Another of these monster guns was so ingeniously concealed in an
imitation thicket that for a fortnight or more it defied the efforts
of scores of airmen to locate it. Though hundreds of airplane
photographs of the country behind the German trenches were brought in
and minutely examined, there was nothing about them to suggest the
hiding-place of a gun of so large a caliber until some one called
attention to the deep ruts left by motor-trucks which had left the
highway at a certain point and turned into the innocent-looking patch
of woods. Why were the wheel-ruts shown on the plate so black? Because
the vehicle must have sunk deep into the soft soil. Why did it sink so
deeply? Because it was heavily laden. Laden wi