Accordingly it soon became the custom of the commanders who saw their works being spied out by an enemy soaring above to send up one or more aircraft to challenge the invader and drive him away. This led to the second step in the development in aërial strategy. It was perfectly evident that a man could not observe critically a position and draw maps of it, or seek out the hiding place of massed batteries and indicate them to his own artillerists, and at the same time protect himself from assaults. Accordingly the flying corps of every army gradually became differentiated into observation machines and fighting machines--or avions de réglage, avions de bombardement, and avions de chasse, as the French call them. In their order these titles were applied to heavy slow-moving machines used for taking photographs and directing artillery fire, more heavily armed machines of greater weight used in raids and bombing attacks, and the swift fighting machines, quick to rise high, and swift to manoeuvre which would protect the former from the enemy, or drive away the enemy's observation machines as the case might be. In the form which the belligerents finally adopted as most advantageous the fighting airplanes were mainly biplanes equipped with powerful motors seldom of less than 140 horse-power, and carrying often but one man who is not merely the pilot, but the operator of the machine gun with which each was equipped. Still planes carrying two men, and even three of whom one was the pilot, the other two the operators of the machine guns were widely adopted. They had indeed their disadvantages. They were slower to rise and clumsier in the turns. The added weight of the two gunmen cut down the amount of fuel that could be carried and limited the radius of action. But one curious disadvantage which would not at first suggest itself to the lay mind was the fact that the roar of the propeller was so great that no possible communication could pass between the pilot and the gunner. Their co-operation must be entirely instinctive or there could be no unity of action--and in practice it was found that there was little indeed. The smaller machine, carrying but one man, was quicker in the get-away and could rise higher in less time--a most vital consideration, for in the tactics of aërial warfare it is as desirable to get above your enemy as in the days of the old line of battleships it was advantageous to secure a position off the stern of your enemy so that you might rake him fore and aft.
The machines ultimately found to best meet the needs of aërial fighting were for the Germans always the Fokker, and the Taube--so called from its resemblance to a flying dove, though it was far from being the dove of peace. The wings are shaped like those of a bird and the tail adds to the resemblance. The Allies after testing the Taube design contemptuously rejected it, and indeed the Germans themselves substituted the Fokker for it in the war's later days.
The English used the "Vickers Scout," built of aluminum and steel and until late in the war usually designed to carry two aviators. This machine unlike most of the others has the propeller at the stern, called a "pusher" in contradistinction to the "tractor," acting as the screw of a ship and avoiding the interference with the rifle fire which the pulling, or tractor propeller mounted before the pilot to a certain degree presents. The Vickers machine is lightly armoured. The English also use what was known as the "D. H. 5," a machine carrying a motor of very high horse-power, while the Sopwith and Bristol biplane were popular as fighting craft.
The French pinned their faith mainly to the Farman, the Caudron, the Voisin, and the Moraine-Saulnier machines. The Bleriot and the Nieuport, which were for some reason ruled out at the beginning of the war, were afterwards re-adopted and employed in great numbers.
It would be gratifying to an American author to be able to describe, or at least to mention, the favourite machine of the American aviators who flocked to France immediately upon the declaration of war, but the mortifying fact is that having no airplanes of our own, our gallant volunteer soldiers of the air had to be equipped throughout by the French with machines of their favourite types. After we entered the war we adopted a 'plane of American design to which was given the name "Liberty plane."
