But their instructions were clear, and each trained pilot knew just what he had to do. Swiftly and still more swiftly they flew. The night mists, growing yet more opaque, promised, favorably. Appincourte Bluff, just beyond the little river, could hardly be seen at all, but the roar of the motors overhead indicated that something might be on the wing. Without question few advance sentries still remained near the ruins that once had been a capacious subterranean chamber. From there the Germans had doubtless expected to emerge in assault, while their artillery made the essential barrage to stay any possible resistance while their infantry crossed the stream. But the Allied bombardment, made possible by Erwin's daring final flight across the Bluff towards his own quarters, had made Appincourte futile so far as that assault went. Still Fritz might be there. He was there -- that is, a few of him. They were watching for a signal - the blue flare of a rocket that should tell Fritz of another air raid. But the noise of motors close above confused his calculations. Why were the Entente airmen flying so low? Might they not be up to more devilment with regard to Appincourte? The blue flare had gone up. But it happened that Fritz did not see it. Fearing now that many bombs might be dropped their defenseless heads, and with the whir of many motors in their ears, all the time growing louder, nearer, the small squad of night sentries, scudded as one man for the small dugout. This had been made immediately after the Bluff was wrecked by the bombardment. In there they cuddled, expecting the deafening explosion of many bombs over or on their heads, determined to fly back to their advanced trenches at the first let-up of the expected deluge. But no bombs descended. The motor thunderings passed, then dwindled, but towards the east. What did that mean? Their sergeant was telephoning hurriedly as to what was happening: "Airplane motors close overhead. No bombing yet. Watch out." Thus it happened that Bauer's first (and last) signal was rendered void insofar as it went. The raiders escaped the German fire for the time being. Moreover, they were puzzled. Why should the Allied "schwein" fly so low, yet do no harm where once they had wrecked things only a few days before? What were they up to, anyhow? This query was not answered at once. The telephones roused the Huns in the front trenches. Yet it puzzled them, too. Hitherto the bombing on both sides had been done mostly from far above. Such skimming the ground across No-Man's-Land might mean anything. Presently the thrum of approaching planes became more and more audible along that portion of the front.