At first this seemed to have little effect, and the Germans ascended rapidly, while their machine gun operators, although as yet unable to use their deadly weapons, sent a hail of revolver bullets whistling through the wings and rigging of the American machine. But now the concentrated fire from the American machine was beginning to have effect. One of the German planes hesitated, quivered, and suddenly its right wing, with its wire stays severed by the machine gun bullets, crumpled up. The crippled aeroplane staggered wildly, suddenly turned on its right side, and pitched steeply downward. The boys in the American airplane gazed at each other with white faces, but they had little time to devote to thoughts of the fallen, for by now the remaining German machine was on a level with them, and its machine gunner opened fire. The Americans, crouching low to avoid the murderous stream of bullets, returned the fire from both their machine guns, with a deadliness of purpose and aim for which the German was no match. Suddenly a tiny flame appeared in the body of the German machine, grew with lightning rapidity, and in a few seconds one side of the machine was enveloped in leaping yellow flames. "Punctured the gas tank!" exulted Lever. "They're done for now." And he was right. The machine gun fire from both fighting planes died out, and the boys could see the Germans vainly trying to beat out the hungry flames. Their efforts were useless, however, and in a few seconds the German machine, a roaring mass of flame and black smoke, dropped downward as swiftly as a stone. As it went, the boys saw two figures hurl themselves out into space, and then everything was hidden in a haze of billowy smoke. "That's awful!" exclaimed Tom, drawing in his breath with a great sigh, while all relaxed from the terrible tension they had been under. "Awful, yes," said Dick Lever. "But it's only what they would have done to us if they had been able. Instead of 'live and let live,' it's 'kill or get killed' in this game." Frank nodded his head gloomily, but none of the boys felt like talking then, and sat silent as their pilot got his bearings and then straightened out swiftly in the direction of the American lines. With the roar of the motor in their ears and the rush of wind past their faces, much of the horror of the deadly air battle was swept from their minds, and they began to enjoy the exhilaration of their first flight. The distant earth streamed rapidly by, like a swiftly flowing river, and a wonderful panorama was spread out below them. It was an exceptionally clear day, and they could see for many miles in every direction. Below them, groups of gray clad figures, after a glance in the direction of the soaring monster overhead, broke for cover, or, shaking impotent fists, trudged stolidly onward, contemptuous of one more danger among the many that daily surrounded them. "No prison camp for us this time," exulted Frank, as he looked down at his enemies.