As a scouting-machine the airplane did prove to be far superior to mounted patrols which used to perform scout-work. In fact, it changed completely the character of modern warfare. From his position high up in the heavens the flying scout had an unobstructed view of the country for miles and he could see just what the enemy was doing. He could see whether large forces of men were collecting for an attack. He could watch the course of supply-trains, and judge of their size. He could locate the artillery of the enemy and come back with information which in former times a scout posted in a tall tree or even in a captive balloon could not begin to acquire. Surprise attacks were impossible, with eyes in the sky. The aviator could help his own batteries by signaling to them where to send their shell, and when the firing began he would spot the shots as they landed and signal back to the battery how to correct its aim so as to drop the shell squarely on the target. The French sprang a surprise on the Germans by actually attacking the infantry from the sky. The idea of attack from overhead was so novel that armies did not realize the danger of exposing themselves behind the battle-front. Long convoys of trucks and masses of infantry moved freely over the roads behind the lines and they were taken by surprise when the French began dropping steel darts upon them. These were about the size of a pencil, with pointed end and fluted tail, so that they would travel through the air like an arrow. The darts were dropped by the hundred wherever the airmen saw a large group of the enemy, and they struck with sufficient velocity to pierce a man from head to foot. But steel darts were not used very long. The enemy took to cover and then the only way to attack him was to drop explosives which would blow up his shelter. At the outset, air scouts were more afraid of the enemy on the ground than in the sky. The Germans had anti-aircraft guns that were fired with accuracy and accounted for many Allied planes. In those days, airplanes flew at comparatively low altitudes and they were well within the reach of the enemy's guns. But it was not long before the airplanes began to fight one another. Each side was very much annoyed by the flying scouts of its opponents and after a number of pistol duels in the sky the French began to arm their planes with machine-guns.