With their clasp knives they cautiously attacked the boards in the wall of the third shed, stopping every now and again to listen. After a while they were able to remove two of the boards, leaving an opening large enough to admit them. Very carefully they climbed in. Dark as the interior had appeared from the outside, they found when they were inside that there was just light enough, filtering through cracks in the wall, to reveal the contents of the shed. The whole interior, except for narrow gangways, was packed with shells and cases of high explosives. Near the door there were shells for field guns and howitzers, and a certain quantity of small arms ammunition. It was clear that the shed was an ammunition depot. Creeping carefully back, they replaced the boards, and went to the middle shed, which they managed to enter in the same way, after the exercise of greater patience, owing to the more constricted space between the shed and the wall of the quarry. Here they found the gun train, and a number of petrol tins: evidently the engine was petrol driven. While Kenneth examined the engine as well as he could in the still dimmer light, wishing he dared to use his electric torch, Harry stole to the front of the shed, and watched the sentry through a crack in the badly fitting folding doors. Kenneth followed him. "Let me know when the sentry’s back is turned," he whispered. "I’ll use my torch then." Harry gave the sign by a scarcely audible hiss. Kenneth made the best use of the few seconds afforded him at intervals. His experience of motor engines had taught him exactly what to look for. And he was prompted, not by mere curiosity, but by a sudden idea which had occurred to him, but which he had not yet mentioned to his companion. The engine was still warm. He knew that it ran very smoothly; it was provided with a very efficient silencer, or he would not have mistaken it for an electric engine. With their customary thoroughness, the Germans had ensured that the movements of their gun train should lack nothing in secrecy. The mechanism was simple, similar to that of an ordinary touring car, except that there were only two speeds and reverse. "Well," he thought, "why not run off with the train, gun and all?" The train had backed into the shed trucks first. They were still coupled to the engine. The load was very heavy; the question was whether he could get up speed in time to escape. Some of the Germans were awake: the sentry was at the door; the feat seemed impossible, and Kenneth dismissed the idea, feeling glad that he had not suggested it to Harry. But before leaving the engine he looked into the tank, and saw that it was half full of petrol. A hiss called him to the door. The sentry was being changed. The new man was grumbling at having had to leave his bed. The voices in the further shed had ceased. "All gone to bed?" asked the sentry who was being relieved. "Yes," replied the other, yawning.