Nor did we only manufacture planes and train men for ourselves. "The Government of the United States," says the Air Service Report, "has paid a striking tribute to the British Air Service by adopting our system of training. The first 500 American officer cadets to be trained went through the School of Military Aeronautics at Oxford, afterwards graduating at various aerodromes in England. These officers formed the nucleus of American schools, which were eventually started both in the United States and in France.... In all about 700 American pilots have passed through our schools.... And when the question of producing a standardised engine was considered every facility was given and all our experience placed at the disposal of the American Government, with the result that the Liberty engine was evolved." Meanwhile the constant adaptation to new conditions required in the force stimulated the wits of everybody concerned. Take aerial photography. The first successful photograph was taken in November, 1914, of the village of Neuve Chapelle. The photographic section then consisted of two officers and three men, with two cameras and a portable box of chemicals. At the present day it contains 250 officers and 3,000 men--with a large training school; and its prints have been issued by the million. Meanwhile the development of our aircraft fire had driven the aerial photographer from a height of 3,000 feet up to a height of 22,000, where, but for invention, he might have perished with cold, or found it impossible to breathe. But intelligence pursued him, providing him with oxygen and with electric heating apparatus in the upper air. And when, on the other hand, he or his comrade swooped down to within a few hundred feet of the earth, in order to co-operate in attack with infantry or Tanks, again intelligence came into play, inventing a special armoured machine for the protection of the new tactics. The growth of "wireless," as a means of air-communication, is another astounding chapter in this incredible story. Only _one_ of the machines which left with the original Expeditionary Force was fitted with "wireless" apparatus, and it was not used till the first Battle of the Aisne, when co-operation with the artillery first began. There are now 520 officers in the "wireless" branch and 6,200 other ranks; while there are 80 "wireless" stations in France alone and several hundred battery stations. "Wireless" telephony, too, has been made practical since 1917; and over a range of some 75 miles has been of deadly use to the artillery, especially at night, when the watcher in the skies becomes aware of lighted aerodromes, or railway stations, behind the enemy lines.