Our bus led the way across the huge unwieldy Forêt de Charbon, patterned in rectangular fashion by intersecting roads, and we arrived at Siègecourt. This is at once a fortress and an industrial town. There are several railway stations around it, and these added greatly to the observers' collection of trains and trucks. The Huns below, with unpleasant memories of former visits from British aircraft, probably expected to be bombed. They threw up at us a large quantity of high-explosive shells, but the shots were all wide and we remained unworried. To judge by the quality of the A.-A. shooting each time I called there, it seemed likely that half-trained A.-A. gunners were allowed to cut their active service teeth on us at Siègecourt. Having squeezed Siègecourt of all movement, we headed for Le Recul. Here the intricate patchwork of railway kept the observers busy, and six more trains were bagged. Then, as this was the farthest point east to be touched, we turned to the left and travelled homeward. It was soon afterwards that our engine went dud. Instead of a rhythmic and continuous hum there was at regular intervals a break, caused by one of the cylinders missing explosion at each turn of the rotary engine. The rev.-counter showed that the number of revolutions per minute had fallen off appreciably. Decreased revs. meant less speed, and our only chance to keep with the others was to lose height continuously. We were then nearly fifty miles from the lines. I noticed the gap in the engine's drone as soon as it began. An airman is accustomed to the full roar of his engine, and it never distracts his attention, any more than the noise of a waterfall distracts those who live near it. But if the roar becomes non-continuous and irregular he is acutely conscious of the sound. When the machine began to lose height I knew there was a chronic miss. V. looked round and smiled reassuringly, though he himself was far from reassured. He tried an alteration in the carburettor mixture, but this did not remedy matters. Next, thinking that the engine might have been slightly choked, he cut off the petrol supply for a moment and put down the nose of the machine. The engine stopped, but picked up when the petrol was once more allowed to run. During the interval I thought the engine had ceased work altogether, and was about to stuff things into my pocket in readiness for a landing on hostile ground. We continued in a westerly direction, with the one cylinder still cutting out. To make matters worse, the strong wind that had been our friend on the outward journey was now an enemy, for it was drifting us to the north, so that we were obliged to steer almost dead into it to follow the set course.