The first phase, then, of the highest grade offensive, the ultimate development of war regardless of expense, is the clearance of the air. Such German machines as are up are put down by fighting aviators. These last fly high; in the clear blue of the early morning they look exactly like gnats; some trail a little smoke in the sunshine; they take their machine guns in pursuit over the German lines, and the German anti-aircraft guns, the Archibalds, begin to pattern the sky about them with little balls of black smoke. From below one does not see men nor feel that men are there; it is as if it were an affair of midges. Close after the fighting machines come the photographic aeroplanes, with cameras as long as a man is high, flying low--at four or five thousand feet that is--over the enemy trenches. The Archibald leaves these latter alone; it cannot fire a shell to explode safely so soon after firing; but they are shot at with rifles and machine guns. They do not mind being shot at; only the petrol tank and the head and thorax of the pilot are to be considered vital. They will come back with forty or fifty bullet holes in the fabric. They will go under this fire along the length of the German positions exposing plate after plate; one machine will get a continuous panorama of many miles and then come back straight to the aerodrome to develop its plates. There is no waste of time about the business, the photographs are developed as rapidly as possible. Within an hour and a half after the photographs were taken the first prints are going back into the bureau for the examination of the photographs. Both British and French air photographs are thoroughly scrutinised and marked.