When the train had passed, they hastened after it, walking just below the crest of the ridge. They had scarcely started when they heard a low screeching of brakes. Stealing on a few steps, and peering over, they saw that the train had stopped opposite the small platform. The men had got out of their truck, and were moving noiselessly but quickly about the truck containing the gun. Orders were given in a low voice. There was a slight grating of machinery and creaking of timber. The recoil cradle of the gun, which still remained on the truck, was being placed on the platform; the gun itself was being loaded. Its muzzle pointed over the railway line towards the trenches. Stuffing up their ears, Kenneth and Harry waited. The gun was fired. They heard the heavy projectile whizz over their heads. Three times the gun spoke; then it was swung round on the truck, and the train moved on to the north-east. Dazed and deafened by the tremendous noise, the watchers followed it along the line. Here was a discovery indeed. It was no wonder that the gun had never been located. But what they had already learnt made them eager to learn more. Where was the gun kept when not in use? Where was the headquarters of the men? If they could find out this, they would have information of real value to carry back with them. They went cautiously along the line, on the look-out for sentries. But the line was not guarded. Its existence was probably known only to the German staff, and it was evidently used only for the gun train. About half a mile beyond the platform, the train came to rest at another. Again the gun was fired: then the train rumbled back. The two men hid until it had passed, then continued along the line in the opposite direction. During its absence they would seize the opportunity to survey this part of the line.