Meanwhile the observer had reached the base of one of the stone piers which supported the bridge. The excited sentries had not noticed his presence, and now he was safely hidden in the gloom of the arch. With the water swirling round his waist he worked feverishly to remove one of the stones. At last it was loosened sufficiently to be withdrawn. In its place he put his precious packet, which was a charge of high explosive. This he secured firmly in position, and then, having set the fuse, he began to return, through the water, to his starting place. Another swift flash illuminated the leaves of the riverside bushes. It was followed by a second thundering explosion, as another bomb burst near the crowded troop train which still had not crossed the bridge. In a few minutes he clambered up the bank and hurried through the magic beauty of the moonlit wood. He reached the edge of the field where he had landed, and stood waiting. He looked at the luminous face of his watch. The pilot was going to allow him fifteen minutes. Fourteen had passed. He knew his friend would not fail him whatever happened, so though he stood, soaking wet and alone, surrounded by the now angry enemy, he did not feel at all alarmed. Overhead he heard the drone of the engine, which suddenly stopped, to be followed by the faint, scarcely-heard hiss of the wires as the machine began to glide downwards to the ground. Soon a shadowy shape moved swiftly across the ground and stopped. The observer ran over to it and climbed quickly into his seat. He shouted to the pilot of the success of his operation, and then with a roar and rush was borne upwards, and to his relief found himself flying swiftly once more through the friendly air. Even as they turned to start on their long homeward journey a great sullen roar rose to them from below, and they saw that no more across the silver streak of the river lay a black line, for now it was obscured by a cloud of smoke, which slowly dissipated and revealed a great gap in the bridge, near which was the red glow of the locomotive that no longer could take forward its carriages loaded with troops destined for a now impossible railhead. That happened in the early days of the war. Swiftly developed the powerful arm of the air. Great were the changes in thought. Mighty the new weapons of destruction.... * * * * * "C.O. wants to see you at once in the Mapping Office." It is four o'clock on September 29, 1917. I hurry to the little hut by the mess and pass through the door. Over the long desk leans the grave-faced squadron commander, the great pioneer of night-bombing. With a pencil and a ruler he carefully studies a map. "Is that you, Bewsher?" he says. "Look here, I want you to go to Namur to-night; do you think you can do it?" "I think so, sir."