They patrolled the country behind the German lines, and watched the smoke curling upwards from a dozen French villages in the enemy's possession. At length they crossed the loop line near Barastre, skimmed along over Ytres, and the Bois Havrincourt; sailed lightly across the silvery streak of the river Exuette, until, beyond the wood and the village they espied the main railway line that threaded its way to Bapaume. "There it is, Fisker. Can you see it?" were Dastral's first words, when he sighted it. "Yes, I see it," came the reply. Dastral had timed his arrival nicely. Scarcely had they reached the railway when out of the eastern horizon a trail of white steam, followed by another and yet another, at intervals of perhaps half a mile, attracted their attention. "Look! There they come, Dastral!" cried Fisker, putting down the glasses and waving his arms frantically to attract the attention of the other three pilots, and to indicate the target, now rapidly approaching. One look in the direction indicated sufficed for Dastral. He made a sudden dip, then gave one of his rapid spirals, at which he was such an adept. This movement of the Flight-Commander's machine was the pre-arranged signal for the rest of the company and meant: "Enemy approaching from the east. Prepare to engage him." The movement was answered by each of the following 'planes. The formation of the flight was altered accordingly, and the machines now fell into their allotted places ready for descent. The three trains were soon in full view, and the first one was just passing the village of Hermies. The trains were of enormous length, and were crowded with troops. What still puzzled Dastral, however, was that there appeared to be no escort of aircraft with them. Again and again, during the approach of the long procession, he had scanned the heavens all around and above him, for a sight of his most crafty foe, Himmelman, for, if the British machines had been sighted, there had been plenty of time for the enemy to bring up his aircraft from the nearest aerodrome. Even yet Dastral was very suspicious. He knew Himmelman only too well already. He was the demon of the air on the western front, and loved nothing better than to make a dramatic entry into a half-finished fight. His greatest and most daring method was to climb out of sight, often up to seventeen thousand feet and more, or better still, to make an ambush in a dark cloud, then suddenly to swoop down, hawk-like, upon his opponent, in an almost vertical nose-dive, and to overwhelm him with a spray of well-directed machine gun fire.