Another phase of air work was the bombardment of enemy territory. Munition factories, railroad junctions, railroad yards far in the rear of the lines were commonly the targets, and a few well-directed bombs might do enough damage, it was thought, to prevent some movement at the front; might interfere with a stream of supplies or with the manufacture of munitions long enough to be of some consequence. It is not yet proved, however, that the from the air, undertaken by both sides, had any material effect upon military events.

The last phase of aviation, the most dramatic and most popular, was, from the point of view of the larger aspects of warfare, the least important. This was the aviation of combat. Its purpose was to protect the balloons and the observation planes of the Allies while they were obtaining the data upon which the conduct of the war depended. This made essential attacks upon German aëroplanes which were attempting to destroy the Allied balloons or observation planes. Another phase was naturally an attempt to destroy the German balloons and observation planes and often led to combats in the air with the German fighting machines sent out to protect their own observers. This work was always dangerous in the extreme and not infrequently important, though it is not yet demonstrated that either the Germans or Allies succeeded in getting control of the air for more than a very brief period or that any of the military victories was the direct result of the fighting in the air. Probably no military event of any consequence took place which did not have vital connection with the air service, but it is probable that the great successes were not due to any one arm of the air service.

During the last two years of the war extraordinary developments were in progress which might have resulted, had the war lasted longer, in great transformations of warfare itself. The aëroplane began to take a direct part in the fighting on the ground. Fighting planes did occasionally annihilate a German division marching to the trenches, or was able to rake a trench with machine gun fire from the air and thus remove the obstacle facing the Allied troops. The great gun batteries located far behind the lines were particularly vulnerable.

In the great offensive of 1918 whole squadrons of aëroplanes fought battles in the air, when hundreds of planes charged each other, laid down barrages of machine gun fire, and even attempted concerted assaults upon large masses of troops, advancing across open ground. Of course, the aëroplane, armed only with a machine gun, could never assault with success prepared trenches or dugouts, but once the troops left their defenses and started to charge across the open, unprotected by artillery, a single aëroplane might do great damage. Columns advancing to the support of the front trenches were also splendid targets for the aviators. The daring of some men was extreme. Garros, one of the first great French aviators, bombed trains, troops, supply depots, from a distance of only one hundred feet above them.

As the war went on, changes in the structure of the aëroplanes were no less remarkable than the increase in the skill of the pilots. Before the war the machines had been barely dependable, had lacked strength and stability, but as the war went on nearly all desirable qualities were developed, and in addition, motors were created capable of carrying heavy weights over great distances and planes were built able to fly in heavy winds or storms. Mechanics learned how to mend the machines while in the air, even repairing the engine itself. Hospital aëroplanes were created and minor operations were sometimes performed in flight. So great was the stability of the planes at the end of the war that part of the machine could be blown away by a shell and the machine would still fly. Bishop, the British aviator, landed with his machine in flames and escaped unhurt, largely because of his confidence that, although the machine was doomed, he would be able to control it long enough to reach the earth.

The real interest of the war centered in these fighting planes. They developed a speed of one hundred and thirty miles an hour, would climb into the air at the rate of one thousand feet a minute, and some carried as many as three rapid fire guns, able to fire four hundred shots a minute. Many great aces were developed on both sides, but although numerous personal exploits are extremely interesting to study, the general tactics of aviation as a whole are really of more consequence in the history of the war.

As always, German tactics reasoned out logically what was to be done and then proceeded to keep the individual within bounds. At first the Allies charged the Germans with cowardice because their aviators kept for the most part over their own lines, but the great German aces explained that if a German plane fell within their own lines the Allies learned none of the German secrets of construction. The object of the fighting planes in any case was to prevent Allied observation and to protect German balloons and observers. This could always be done within the German lines. It was therefore foolhardy to venture beyond them. Immelmann developed first among the Germans a method of attack upon an enemy plane which combined the maximum chances of success with the minimum danger. The aëroplanes were at first not armed at all and then carried guns which shot only between the blades of the propellers, straight in front of the machine. Let the aviator keep above, behind, below, or at either side of his adversary and he was perfectly safe. Immelmann, therefore, cruised around at high altitudes, preferably in the clouds; when an Allied plane appeared, he waited until it passed beneath him. He then shot straight down upon it, carried by the force of gravity at a terrific speed and intending to pass just behind it. When almost upon the enemy he fired as many shots as he could, and was then carried by the speed of his own flight below and beyond his enemy, protected from his enemy's fire, partly by his position and then, as he passed in front of him, by his speed. He would never wait to see whether the enemy fell or not, nor attempt to reengage him. To do that was to fight at a disadvantage.

Boelke, another great German ace, pointed out the advantage of fighting in pairs and later in squadrons. Several German planes would engage a smaller number of Allied planes, but preferably a single plane. This increased the chances of their success and diminished the danger. Commonly, if outnumbered, the Germans turned tail and fled. They did not propose to take risks; the pilot and machine were too valuable to be lost in such fashion. Richthofen, perhaps the greatest of the German aviators, invented camouflage in the air and developed maneuvering by a squadron of aëroplanes. His favored method was to attack in long file, he himself heading the tango circus as it was called. He scorned concealment in his own case, however, and painted his machine bright red so that it might always be known.

One of the most successful French aviators was Fonck, who destroyed ten German planes without himself being scratched. On May 9, 1918, he went up alone, as Allied machines frequently did, to meet three German planes, each carrying two men, and, therefore, more than doubly dangerous. Two he destroyed in ten seconds and the third five minutes later. That afternoon, he met five German planes in formation, dove into them from above, and sent down three, the remainder escaping. The whole six had been shot down with an average of six cartridges per plane. Bishop, the Canadian aviator, was ordered to return to England to take charge of instruction and went out for a last trip across the lines. He was gone twelve minutes and brought down five German planes. The true secret of success in the case of these exceptional men was primarily deadly marksmanship. Their skill as aviators was apparently a secondary consideration, although none of the tricks in flying was without its value and sometimes meant the difference between destruction and safety. Their coolness, confidence, and self-control under all circumstances were the great qualities which accounted both for their marksmanship and for their ability to fly.

The greatest of aviators, however, typifies the Allied methods and, as well, the romance of the war. Guynemer, a young Frenchman, physically rejected by all sections of the service more than once, only twenty-three years old when he died, exemplified the reckless courage and daring of the Allied tactics in the air. He courted rather than avoided danger, gloried in risks, preferred to fight several German planes at once, and commonly returned from a trip with his clothing and plane riddled with bullets. His favorite method of attack was to approach his adversary from below, perform the difficult tail spin, which stood his plane on its tail, immediately below his adversary, and bring him down with a stream of bullets through the bottom of his machine.

No single character of the war so attracted the admiration of the French people. He seemed to them to embody all that quality of French youth most precious to preserve. They seemed to say of him, "Here is the pattern of the young men of France; look upon it, and copy it: it is the best; it is France." While everything about him was burning truth, it seemed as if the truth was already legend. The subtle perfume of mysticism appeared to hang about him. He died in combat, September 11, 1917. The official citation read: "Like a legendary hero fallen in the full measure of glory after three years of ardent combat, he will remain the purest symbol of the qualities of the race: indomitable tenacity, fierce energy, sublime courage. Animated by the most unshakable faith in victory, he bequeathes to the French soldier an imperishable remembrance which will exalt the spirit of sacrifice and stir to the noblest emulation."

One of his intimate friends wrote: "I have known his intrepidity, his tenacity, his fascination. Duty of combat was for him a religion. He had an iron will. He was upright as a sword, pure as a diamond, and utterly absorbed in the struggle which he carried on to the detriment of a constitution already frail. . . . He was of a finer essence than ourselves, inspired with a sacred fire which passed our understanding. He fell amidst forty enemy aëroplanes, of which he had brought down one, one arm was broken, a ball was in his head, and a smile was on his lips."