But suddenly a new danger threatened. A fresh body of German troops had worked its way to a position where it could attack the American right flank, which was but thinly held because for the time being the bulk of the forces were engaged in pressing the advantage gained at the center. If the enemy could turn that flank and throw it back in confusion on the main body, it might lead to serious disaster. At the point where Frank and his comrades were fighting, there was a nest of machine guns that commanded the space over which the new enemy forces were bearing down on the threatened flank. Several of the gun crews had fallen, and the guns were temporarily unserved. There was no time to wait for orders. Another minute and the guns would be in the enemy's hands. "Quick, Bart! Come along, Billy and Tom!" shouted Frank, as he rushed toward the guns. His chums were on his heels in an instant. Quick as a flash, the guns were aimed, and streams of bullets cut the front ranks of the attacking force to ribbons. Volley after volley followed, until the guns were so hot that the hands of the young soldiers were blistered. But the hardest part of their work was done, for now fresh guns had been brought into position and the flank was strengthened beyond the power of the enemy to break. Frank's quick thought and instant action had averted what might have been a calamity that would have decided the fortune of the day. "Good work, old man!" panted Bart, when in a momentary lull he could gain breath enough to speak. "Yours as well as mine!" gasped Frank, as he dashed the perspiration from his forehead. "If you fellows hadn't been right on the job, I couldn't have done anything worth while." Regular crews had now been assigned to take their places, and resuming their positions in the ranks the young soldiers plunged once more into the hand-to-hand work at which they were masters. The issue was no longer in doubt. The scale had turned against the Germans and they were retreating. But they went back stubbornly, giving ground only inch by inch, and in certain scattered groups the fighting was as furious as ever. As far as might be, they kept together, but as the swirl of the battle tore them apart, Tom and Billy were lost sight of by Bart and Frank, who were laying about them right and left among the enemy. A sharp exclamation from Bart caused Frank to turn his eyes toward him for a second. "Hurt, Bart?" he queried anxiously. "Bullet ridged my shoulder," responded Bart. "Doesn't amount to anything, though. Look out, Frank!" he yelled, his voice rising almost to a scream. Frank turned to see two burly Germans bearing down upon him with fixed bayonets. Bart sought to engage one of them, but was caught up in a mass of combatants and Frank was left to meet the onset alone. Quick as a cat, he sidestepped one of them, and putting out his foot tripped him as he plunged past. He went down with a crash, and his rifle flew from his hands.