Overhead, a machine-gun suddenly burst into a rattling roar, the sound sweeping above them with incredible speed. Another gun answered it. Abruptly, the whole sky above them was an inferno of such tearing noises and immediately after they began a multitudinous bellowing set up. Airplanes on patrol ordinarily kept their engines muffled, in hopes of locating a tank below them by its noise. But in actual fighting there was too much power to be gained by cutting out the muffler for any minor motive to take effect. A hundred aircraft above the heads of the two strayed infantrymen were fighting madly about five helicopters. Two hundred yards away, one fell to the earth with a crash, and immediately afterward there was a hollow boom. For an instant even the mist was tinged with yellow from the exploded gasoline tank. But the roaring above continued--not mounting, as in a battle between opposing patrols of fighting planes, when each side finds height a decisive advantage, but keeping nearly to the same level, little above the bank of cloud. Something came down, roaring, and struck the earth no more than fifty yards away. The impact was terrific, but after it there was dead silence while the thunder above kept on. Sergeant Coffee came leaping to Corporal Wallis' side. "Helicopters!" he barked. "Huntin' tanks an' pill-boxes! Lay down!" He flung himself down to the earth. Wind beat on them suddenly, then an outrageous blast of icy air from above. For an instant the sky lightened. They saw a hole in the mist, saw the little pill-box clearly, saw a huge framework of supporting screws sweeping swiftly overhead with figures in it watching the ground through wind-angle glasses, and machine-gunners firing madly at dancing things in the air. Then it was gone. "One o' ours," shouted Coffee in Wallis' ear. "They' tryin' to find th' Yellows' tanks!" * * * * * The center of the roaring seemed to shift, perhaps to the north. Then a roaring drowned out all the other roarings. This one was lower down and approaching in a rush. Something swooped from the south, a dark blotch in the lighter mist above. It was an airplane flying in the mist, a plane that had dived into the fog as into oblivion. It appeared, was gone--and there was a terrific crash. A shattering roar drowned out even the droning tumult of a hundred aircraft engines. A sheet of flame flashed up, and a thunderous detonation. "Hit a tree," panted Coffee, scrambling to his feet again. "Suicide club, aimin' for our helicopter." Corporal Wallis was pointing, his lips drawn back in a snarl. "Shut up!" he whispered. "I saw a shadow against that flash! Yeller infantryman! Le's get 'im!" "Y'crazy," said Sergeant Coffee, but he strained his eyes and more especially his ears.