Still quite a distance away, the American infantry had wheeled sharply to the right. "Flank attack," said Hal briefly, "but it leaves us high and dry." "Well," said Bowers, "I've heard that these contraptions," referring to the tank, "carry signal flags." "We'll hoist one," said Hal briefly. "They may see it." He climbed back into the tank, reappearing shortly with a small flag which he ran up on the turret. "Now all we can do is sit down and wait." "And pray that the Germans don't arrive in force first," Bowers added dryly. The two sat down in the sunlight and followed the course of the battle in the distance. Gradually the American charge slowed down. From beyond, Hal could see the ranks of the gray-clad hosts as they emerged from the German lines farther back to charge the American infantry. "They'll get all the fight they want," said Hal. "And more," agreed Bowers. Directly Hal caught the roar of wings coming toward them. He glanced aloft. An American liaison plane was approaching. Bowers let out a cheer. The aeroplane approached close enough to see the signal on the turret of the tank, and signalled back that reinforcements would be sent. Then it flew away again. "In which case," said Hal, "we might as well get busy again." "My sentiments, sir," agreed Bowers. They re-entered the tank, leaving their prisoner still tied on the ground. The young German eyed them angrily as they disappeared within. "Machine gun nest to the right, Bowers," called Hal, who again manned the gun. Without further words, Bowers headed the tank in that direction. "They're firing explosive bullets, sir," called Bowers coolly a few moments later as the earth flew high to one side of the tank. Previous to this, the use of explosive bullets against tanks had been questioned, but Hal was bound to believe the evidence of his own eyes. In the instance where the use of explosive bullets had been reported before, they had been effective in that they had set fire to gasoline in the travel tanks lashed to the machine's sides. Hal, recalling the details of that battle, was thankful that there were no tanks of gasoline lashed to the tank in which he and Bowers were confined. Now, it seemed to Hal and Bowers, they were in the center of a group of machine-gun nests. Hal fired as rapidly as he could bring his gun to bear. But the Germans had developed wisdom. The machine gunners crouched down in their holes whenever the tanks were turned on them, and let gunners in other nests take up the fight. A surprising number of machine-guns were developed around the tank. Evidently the gunners had kept under cover during the previous activities of the tank and only popped up when it seemed safe. It began to grow uncomfortably hot in the tank. The backplace which separated the engine compartment from the turret and steering room became almost red hot.