The patrol boat was less than four hundred yards away, and travelling at a great pace. It was almost within hailing distance. Ruxton could even count the occupants at that distance. He was certain there were six at least. The other patrol boat had contained only two officers besides the engineer. The difference was significant. He followed his host into the conning-tower and the steel door was closed with a slam behind them. It automatically sealed itself. The Prince's voice at the foot of the steel companion-ladder, leading up to the chief officer's post, rang out sharply. "Submerge!" Then he turned to his companion. "We will go below. We will go forward, where Ludovic will join us in a moment. I will show you that which I hope may interest you. We have seen the last of Von Salzinger and his command--for some time." The nervous energy of the Prince led Ruxton at a rapid rate. They passed down the companion, and, instead of entering the saloon, turned for'ard, down an alleyway which took them past the moving steel bowels of the vessel. The low purr of the great Diesel engines fell pleasantly upon the Englishman's ears. There was no hiss of steam. There was none of the clanging of high-pressure mechanism. Just a steady, powerful throb which vibrated throughout the length of the vessel's hull, and told him of the enormous mechanical effort going on. They left the engine-rooms behind and passed by the kitchens, to which very careful and elaborate attention had been given. They left the quarters of the crew, beautifully kept and equipped, and without a sign or suggestion of that inferiority of appointment which is to be found on all commercial vessels. They passed a number of carefully disguised bulkheads, and finally came to a doorway in a steel bulkhead which seemed to mark the limit of the forward end of the vessel. The Prince withdrew a key from his waistcoat pocket. He opened the door, and both of them passed within. Once the door was closed he slid his fingers up the steel wall in the darkness and pressed a switch. In a moment the room was flooded with light, and Ruxton blinked under its power as he gazed about him. The Prince was standing in front of him gazing half smilingly at the expression of his face. He was seeking that surprise which to his simple nature meant much satisfaction. Nor was he disappointed. The moment Ruxton recovered under the dazzling glare he realized that that which he now beheld he had witnessed in the vessel at Borga, whence he had brought the cylinders. This was the U-rays room of the private submersible. It was--yes, it was the U-rays in active operation. A question promptly sprang to his lips. "But the light is perfect," he said. "There is nothing wrong with it here?"