It has also become increasingly difficult for the airman to gather absolutely trustworthy data concerning the disposition and movement of troops. Small columns are now strung out along the highways to convey the impression that the moving troops are in far greater force than is actually the case, while the main body is under the cover offered by a friendly wood and is safe from detection. The rapidity with which thousands of men are able to disappear when the word "Airman" is passed round is astonishing. They vanish as completely and suddenly as if swallowed by the earth or dissolved into thin air. They conceal themselves under bushes, in ditches, lie prone under hedgerows, dart into houses and outbuildings—in short, take every cover which is available, no matter how slender it may seem, with baffling alacrity. The attenuated column, however, is kept moving along the highway for the express purpose of deceiving the airman.

Advancing troops also are now urged to move forward under the shelter of trees, even if the task entails marching in single or double file, to escape the prying eyes of the man above. By keeping close to the line of trunks, thus taking full advantage of the overhanging branches, and marching in such a manner as to create little dust, it is possible to escape the aerial scout.

The concealment of cavalry, however, is somewhat difficult. An animal, especially if he be unaccustomed to the noise of the aeroplane, is likely to become startled, and to give vent to a frightened and vociferous neighing which invariably provokes a hearty response from his equine comrades. The sharp ear of the airman does not fail to distinguish this sound above the music of his motor. Again, he has come to regard all copses and stretches of undergrowth with suspicion. Such may or may not harbour the enemy, but there is no risk in making an investigation. He swoops down, and when a short distance above the apparently innocent copse, circles round it two or three times. Still undecided, he finally hurls a bomb. Its detonation invariably proves effective. The horses stampede and the secret is out. Even foot soldiers must be severely trained and experienced to resist the natural inclination to break cover when such a missile is hurled into their midst.

Frequently a force, which has laboured under the impression that it is safe from detection, has revealed its presence unwittingly and upon the spur of the moment. If the men be steeled against the bomb attack, it is almost impossible to resist the inclination to take a shot when the airman, swooping down, ventures so temptingly near as to render him an enticing target almost impossible to miss. As a rule, however, the observer is on the alert for such a betrayal of a force's existence. When the bomb fails to scatter the enemy, or the men are proof against the temptation to fire a volley, a few rounds from the aeroplane's machine gun often proves effective. If the copse indeed be empty no harm is done, beyond the abortive expenditure of a few rounds of ammunition: if it be occupied, the fruits of the manoeuvre are attractive. Cunning is matched against cunning, and the struggle for supremacy in the art of craftiness is keen.

The French Flying Corps have had recourse to an ingenious ruse for accomplishing two ends—the one to draw concealed artillery fire, and the other to pre-occupy the airmen. Two German aerial scouts observed a French machine flying at a somewhat venturesome height over their masked artillery. Divining the reason for the hostile intrepidity they gave chase. Circling round the French machine they assailed it with machine-gun fire. The enemy appeared to take no notice but continued his gradual descent in a steady line.

Presently the German airmen, having drawn sufficiently near, observed that the French aviator was inert. Had he been killed? Everything pointed to such a conclusion, especially as they had raked the aeroplane fore and aft with bullets. But still suspicious they continued their circling movements, their attention so concentrated upon their quarry that they had not observed another move. It was the crash of guns from their masked artillery which broke in upon their absorption. Looking round, they observed three French aeroplanes soaring around and above them at high speed. Scarcely had they realised the situation before a spirited mitraireuse fire was rained upon them. One of the German aeroplanes was speedily disabled. Its fuel tank was riddled and it sank rapidly, finally crashing to earth in the deadly dive head foremost, and killing both its occupants in the fall. The second aeroplane hurried away with its pilot wounded. In the excitement of the aerial melee the first French aeroplane had been forgotten. It was now scarcely 100 feet above the German artillery. A capture appeared to be imminent, but the Germans received a rude surprise. Suddenly the aeroplane exploded and a hail of shrapnel burst over the heads of the artillerymen.

The circumstance was decidedly uncanny, but after two or three such experiences of exploding aeroplanes the matter was explained. The apparently helpless aeroplane was merely a glider, which, instead of carrying a man, had a booby-trap aboard.

It appears that the French airmen have found a use for the aeroplanes which are considered unsafe for further use. The motor and propeller are removed and the dummy of explosives is strapped into position. The laden glider is then taken aloft by means of an airship, and in the concealment of the clouds is released, the rudder being so set as to ensure a gradual vol-plane towards the suspicious position below. The explosive cargo is set with a time fuse, the arrangement being that the contents will be detonated while the machine is near the ground, unless this end is accelerated by a well-planted shell from an anti-aircraft gun. The decoy glider is generally accompanied by one or two aeroplanes under control, which keep under the cover of the clouds until the hostile aviators have been drawn into the air, when they swoop down to the attack. The raiders are fully aware that they are not likely to become the target of fire from the ground, owing to the fact that the enemy's artillery might hit its friends. Consequently the antagonistic airmen are left to settle their own account. In the meantime the dummy machine draws nearer to the ground to explode and to scatter its death-dealing fragments of steel, iron, and bullets in all directions.

Possibly in no other phase of warfare is subterfuge practised so extensively as in the concealment of guns. The branches of trees constitute the most complete protection and guns are placed in position beneath a liberal cover of this character. The branches also offer a screen for the artillerymen, who can lurk beneath this shelter until the aeroplane has passed. To complete the illusion dummy guns fashioned from tree trunks and the wheels of useless limbers are rigged up, and partially hidden under branches, the idea being to convey the impression to the man aloft that they are the actual artillery.

The aerial scout observes the dummies beneath the sparse covering of branches. Congratulating himself upon his sharp eyesight, he returns to his base with the intelligence that he has found the enemy's guns he indicates their position upon the map, and in some cases returns to notify the position of the weapons by smoke-ball or tinsel, when they are immediately subjected to a severe bombardment. He follows the shell-fire and sees the arms put out of action. He returns to camp satisfied with his exploit, oblivious of the smiles and laughter of the hostile artillerymen, who have their guns safely in position and well masked some distance away. The dummies are imperfectly concealed purposely, so that they may be discovered by the aerial scout, while the real guns are completely masked and ready to belch forth from another point. In one or two cases the dummies have been rigged up in such a manner as to convey the impression, when seen from aloft, that a whole battery has been put out of action, barrels and wheels as well as broken limbers strewing the ground in all directions.