The air was "stiff" with machines as GV 7 began to climb steadily. Derek's whole attention for the time being was to avoid certain "unhealthy" spots where high-velocity shells from the British heavies screeched unceasingly. There were other shells which he might not be able to avoid--those coming from the opposite direction--for he knew that it was not an uncommon occurrence for a 'plane to get in the way of a high-velocity projectile and to vanish into fragments. In the hollows wreaths of white mist still clung: danger-spots concealing swarms of German troops who had been rushed up under cover of night in spite of the terrific barrage of the guns and bombs from the British air-craft. A few miles beyond the irregular line of contesting foes a Hun sausage-balloon rose rapidly, swaying and jerking at the end of a two-thousand-feet length of wire. In less than three minutes it was spotted and brought down by a direct hit, while a second, in the act of ascending, was promptly hauled down to earth. Suddenly GV 7 side-slipped, pitching violently in a tremendous air-current. A German eight-inch--a missile that arrived some seconds before its screech was heard--had passed within a few feet of the starboard longeron. The observer turned and grinned at the nearest machine-gunner. It was his way of expressing the fact that they had had a very narrow shave. Derek, too, realised the danger, although his attention was mainly directed towards his task of piloting the battleplane. Occasionally checking his position by means of his map, he held on until it was time to dive to the attack. Viewed from a height of three thousand feet the battlefield lost much of its sordid horror. The old trenches, overrun by the Allies some eighteen months previously, were barely discernible. Hardly anyone expected that they would again prove to be the scene of a sanguinary struggle. New shell-holes contrasted forcibly with the older craters, but of new defensive work there was little to be seen. So rapid had been the German onrush that the British on the defensive had but little time to reorganize. They contented themselves by holding desperately to every bit of cover, receiving and giving hard knocks in characteristic bull-dog fashion. Miles behind the opposing line the air was thick with smoke from burning dumps and stores. Here and there were low mounds of rubble that once were prosperous villages, some others rebuilt only a few months previously to suffer again from an advance of the modern Hun. Here and there guns, scorning the use of camouflage, were firing with open sights at the dense field-grey masses, while farther back on both sides the heavies were exchanging tokens of mutual hate.