preceded it, in the use of aviation as an offensive and defensive arm of military service. The airplane had been demonstrated as really practicable for navigation of the air only since 1908, when the Wright brothers had given their tests in Paris. For some time after that, it was thought of chiefly in connection with sports, and realization of its great importance in war was slow in coming. Even when the military authorities of the various nations took the matter up, they thought of it chiefly as an aid in reconnoissance. It could go where human spies or scouts could not. No trenches or entanglements could hinder it from seeking out the location and movements of the enemy. But its enormous value for other work was apprehended dimly if at all. This was shown by the comparatively small number of planes possessed by the belligerents when the war started. Germany, the best equipped of all the warring nations in this respect, had not quite 1,000; England had only 250, and France had barely 200.
As a scout, the airplane may be said to have met expectations. The movements and concentrations of the enemy were detected with a fair amount of success. It was not wholly and always reliable, however, especially as the war progressed, and both sides grew expert in camouflaging their movements and taking advantage of darkness for withdrawals and renewals of troops. Two notable failures of aerial observers occurred when the Germans were able to concentrate vast masses of men on a Verdun sector in 1916 with the French generals all at sea as to the direction from which the attack was coming, and again when Hindenburg was able to withdraw his men from the Arras salient in March, 1917, without the Allied aviators having learned of the movement. The reasons for these occasional failures can be readily understood. The aviator has to fly so high to avoid attack from anti-aircraft guns, or so fast to escape the attack of enemy airmen, that his opportunities of observation are lessened. A height of less than 10,000 feet was considered unsafe, as anti-aircraft guns developed in range and accuracy during the progress of the war. Under such conditions, to which must often be added unfavorable weather, accurate observation was often impossible. Still, with all these handicaps the aerial service justified itself as a valuable observation arm of the service.
At sea also its value was demonstrated. The seaplane soaring in the air could detect the wake of a submarine more readily than it could be seen from the deck of a vessel. The "mother ship," on which the seaplane could descend,
