On and on they went, and nearer and nearer to the scene of actual battle they came. They passed the third-line trenches, and now, in places, they seemed to be in a straight line with some of the concealed artillery that was pounding away at the enemy in terrible detonations that shook and rocked the ground every minute. At the second-line trenches their orders called for a halt. They did not have to be told that there was "something doing." The road, so far as the eye could reach backward over the route they had traveled, was a constantly moving line of motor trucks, coming forward with men and shells, while out ahead of them, tremendous and menacing, big tanks--the biggest things the boys ever had seen propelled on wheels or tractors--were pursuing their uneven course toward the front, in preparation for a new kind of assault. "They look like miniature battleships on land, don't they?" exclaimed Slim. The others agreed that it was about the best description that could be given of these massive fighting machines, equipped with guns and men, that could travel with their own power practically anywhere, across shell holes, over trenches, through barbed wire--the most human piece of war mechanism that had yet made its appearance on the battlefield. Summons to a long-delayed meal gave a welcome interruption to their guesses as to just what their first duties would be, and they had scarcely finished their substantial rations of food when an orderly informed Lieutenant Mackinson that he was to report at once to the field headquarters. "Await me here," he said to the five men under his immediate command. "I probably will be only a short time." And, indeed, it seemed to them that he had hardly time to reach the headquarters when he was seen returning hurriedly. He gave some hasty instructions to the chauffeur, and the latter immediately began a quick examination of his engine and tires, which promised another early move. "We go forward as far as we can by automobile again," the lieutenant informed them, "and after dark to-night we are to establish an outlying communication from the farthest skirmish points to headquarters." Almost as he finished the sentence, they were started, but now their progress frequently was impeded, and occasionally a shell broke so close to them as to jar the machine from its course. None of the men in the rear seats of that car were cowards, but, aside from Hoskins, it was their first experience under actual fire, and they marveled at the coolness of the driver, who seemed not to mind at all the dangerous quarters they were in. When they climbed out of the machine, half an hour later, Joe remarked upon it in tones of open admiration. "It's nothing," the youthful chauffeur replied. "You'll get used to it, too." As he turned the automobile and started backward, Slim suddenly remembered that they hadn't even heard his name.