It was the first time either of the two boys had ever seen this rapidly moving vehicle of warfare. The open flat cars were protected by thick sheets of steel, behind which were mounted many small guns and rapid-firers. These armored trains already had given good accounts of themselves in other parts of the long line of battle, particularly in Belgium, in the earlier days of the struggle, and were things of terror to the German troops. The train beside which the two lads now stood was ready for instant action. The gunners were at their posts, ready to go forward at a moment's notice. The engineer and firemen stood beside the huge engine. In the distance the sound of firing could be heard, and occasionally a shell burst close to where the boys were standing. But they had been through their baptism of fire, and paid little heed to these messengers of death. "They say that these trains have proven immense factors in sudden raids on the enemy," said Chester. "Yes," agreed Hal, "and it is easy to see that among light armed troops they could do great execution. It would even take very heavy artillery fire to make an impression on those steel sides. Besides----" He broke off with a sudden exclamation. "Look out," he cried, and leaped back, pulling Chester forcibly along. A second later and there was a terrific explosion. A German shell had burst within a few feet of where the two lads had been standing. A crowd of troopers, who had been idling about a few yards from the train, disappeared with the deafening report, and when the smoke had cleared away they were nowhere to be seen. They had been blown to atoms. The boys rushed forward, but, even as they did so, they halted at the sound of a sudden cry, and, turning their faces up the track, they beheld a mounted officer galloping swiftly toward them. An officer dropped off one of the cars of the train, which, fortunately, had not been touched by the explosion, and hurried to meet the newcomer. "Who is in charge of this train?" demanded the horseman, throwing himself from his mount without waiting for the animal to come to a stop. "I am," was the officer's brief response. "You are ordered to proceed forward at once under full speed," was the command. "The Tenth Royal Dragoons are hemmed in by at least 10,000 Germans two miles ahead, and unless you arrive in time they will all be slaughtered." The officer in command of the train looked hurriedly about. "Hicks!" he called loudly. "Hicks!" There was no reply, and the officer shouted again. Then Hal stepped forward. "If Hicks was your engineer," he said, "there is no use calling him. He is dead." "Dead?" exclaimed the officer. "Yes; that shell struck right beside him. The fireman also was killed." "Great Scott!" exclaimed the officer. "Then what am I to do? Hicks was the only engineer with us right now. The others have gone to their quarters, and by the time I could get them here it would be too late."