Rifle bullets are effective against aëroplanes up to a height of about 5000 feet. Observers fly just above this altitude, at about 5500 feet, since they wish to fly as low as possible and yet be reasonably safe. Aviators have told me that this height is so well recognized that they nearly always encounter other observers in the same plane. Aëroplanes, flying at a height of 5500 feet, can observe the movement or presence of large bodies of troops and the flashes of artillery. They cannot observe very much else at that height. They seem to be able to descend suddenly for a short time to a very low altitude when it is necessary and, in a large percentage of cases, to escape. British aëroplanes have made reconnoissances at an altitude of only one hundred yards. Aëroplanes have made surprises in war nearly impossible, since in modern warfare it would be necessary to shift at least a division to produce any effect, and the movement of such a number of men would certainly be visible to aëroplanes during the daytime. If such a movement were performed at night, the presence of the division in a new spot would almost certainly be detected by the aëroplanes in the morning. The possession of a large and efficient aëroplane corps reduces the surprises of war very nearly to nil, and proportionately increases the importance of preparedness and of tactics. The German aviators (and in fact all German observers, such as infantry and cavalry patrols) make it a principle to avoid, if possible, any combat; this is, of course, interpreted as cowardice by the Allies, who seem eager for a fight on any terms. There is a distinct reluctance among aviators for engaging in aërial duels. As one French aviator said to me: "You are both killed and that does no one any good." This reluctance is fairly universal, except with British flyers.