“Why, all my life I have been trying to guess what lay on the other side of the hill!”--THE DUKE OF WELLINGTON. One day, while I was gazing at a German working-party grubbing like ants on a far slope behind the enemy lines, a hawk glided swiftly and strongly into the field of my telescope. It hung almost motionless in the clear summer air, high up above the green valley, its powerful wings outspread, the very incarnation of waking watchfulness. And I found myself wondering of what the hawk reminded me, poised aloft, now swooping a little this way, now that, until a low droning in the azure far above gave me my clue even as an aeroplane glittered into sight. The aeroplane stood out, almost motionless as it seemed to me, over the German lines, while with a “pom-pom-pom!” the German anti-aircraft guns ringed it round in puffs of white smoke. Like the hawk that continued to hover over the valley, it was watching--watching. Like the hawk’s, its searching glance plunged down into the animate life far below, the life that pursues its normal round unperturbed because it knows it cannot escape from the eyes in the sky. The aeroplanes are the eyes of the army. They alone have made possible the war of positions. From the Alps to the North Sea the warring nations of Europe are hidden in the ground, but their eyes are far aloft. It is the alliance between the mole and the hawk. While the man in the trench uses the periscope to observe from his safe shelter the enemy trench across the way, the army commanders in the rear peer through the eyes of the aeroplanes into the enemy trenches and into the enemy country far behind the firing-line. The most important contribution which this war is destined to make to our knowledge of warfare lies in the development of the use of military aircraft. The aeroplane has revolutionized warfare, because it has practically removed from war the element of surprise. The only hope that the modern General has of maintaining the fog of war lies in the weather, which, in more than one instance in this war, has effectually veiled from peering eyes aloft movements which are destined to have a decisive influence on the operations. The aeroplane has relieved the cavalry of the greater part of its functions. If our cavalry are serving dismounted in the trenches, and their horses growing round of belly, it is the fault of the aeroplane. Sir John French has defined the functions of cavalry as threefold: to reconnoitre, to deceive, to support. The aeroplane has entirely usurped the first of these three roles, and has rendered the second illusory. Only rain and mist can safely hope to obscure the movements of an army from the eyes of the watcher in the skies.