Then, swinging back into line, the tank in which Derek had "signed on" as an unofficial member of the crew pressed forward towards another belt of almost intact wire, against which hundreds of demoralized Boches were held up in their precipitate retreat. On breasting the ridge the armada was greeted by a heavy fire at short range. Several tanks came to an abrupt halt, burning fiercely from end to end. Others, regardless of a heavy fire, held resolutely on their course, methodically flattening out obstacles and crushing Boche machine-gunners out of existence. Suddenly an anti-tank bullet passed through the forepart of the tank on which Derek was busily engaged with his machine-gun. The steel core passed through the head of the pilot, glanced from a metal girder, and penetrated the chest of the Commander. Not content with this, the deadly missile pulverized the magneto and disappeared through the floor of the tank. Promptly the huge land-fort came to a standstill. To all appearances its term of life was approaching its end. Flames began to issue from one of the carburettors. In another moment the tank would have become a raging inferno but for the action of one of the drivers. Grasping a "pyrene" extinguisher, he directed the oxygen-destroying chemical upon the flames. Almost immediately the fire was quenched, but the noxious fumes from the extinguisher made the interior untenable. Even those of the men who wore gas-masks found that these were no protection from the choking fumes, for owing to the showers of metallic splinters in the interior of the tank not a mask remained serviceable. "Out of it, lads!" spluttered the second in command, a subaltern of the Tank Corps. His voice trailed off into a queer little squeal of pained surprise, for a bullet, passing through a rent in the tank's side, shattered his left arm at the wrist. Quickly, yet in an orderly manner, the evacuation was carried out. The wounded men were assisted to a place of doubtful shelter afforded by an abandoned trench, while Derek and the eight unscathed members of the crew followed to await developments. Even as Derek crouched in the shallow trench, the greater part of which had been flattened out by tanks crossing the obstruction, he noticed an officer in the uniform of a major of the Tank Corps running along the irregular parados. "Back, back, all of you!" he shouted. "Pass the word along. Signal to the Tank-Commanders. We're held up, and the ground is heavily mined. Retire!" CHAPTER XV Outed