"That must be Sladek's plane, keeping track of us," nodded Ford. "I understand his ship is ready to go at a moment's notice. He's gathered a crew of thirty of the toughest characters on the waterfront and promised them all a good slice of the bullion if he gets it. Knowing Sladek as I do, I wouldn't put much faith in his word if I were a member of that crew." When the _S-18_ was clear of the lower bay, the warning bell sounded and everyone on deck went below. Hatches were made fast and every member of the crew went to his station. For Tim there was nothing to do but stand in the control room and watch the activities of the others for he was not experienced enough in submarine operation to be placed at one of the important posts. Commander Ford's commands were crisp and alert. The Diesels were silent and only the faint humming of the big electric motors could be heard. Then the _S-18_ moved on a slight angle and Tim knew they were going below. He had encountered a good many queer sensations in an airplane, but none quite so alarming as the one which gripped him now. He was actually going under the surface with only the thin steel walls of the submarine to ward off the destructive force of the water. Tim glanced around the control room. Commander Ford was standing with his eyes glued to the periscope. Pat was at the main diving rudders. Forman Gay and Erich Gaunt were at the valves which controlled the ballast tanks. All were silent, intent on their work. "Are the forward ballast tanks flooded?" snapped the commander. "Yes sir," replied Pat. "How about the after tanks?" "They're flooded." "Then level off and hold her at forty feet." The submarine resumed her even keel, but Tim knew they were forty feet below the surface. Commander Ford left his post and visited each compartment, making sure that everything was functioning smoothly. When he returned, he said calmly: "We'll go a little deeper." The diving rudders were inclined again and the _S-18_ nosed its way deeper into the water. Tim watched the depth gauge, fascinated. The needle was marking the distance steadily. Sixty, seventy, eighty feet they went. Now they were moving downward again. Ninety, ninety-five and then a hundred. George Gadd, the engineer, came into the control room. "Everything's all right so far," he reported. "Then we'll go the rest of the way," decided Commander Ford. Tim knew what the order meant. They were going to the bottom, going down to make absolutely sure that the _S-18_ was ready for the Caribbean treasure hunt. CHAPTER SEVENTEEN On the Bottom The depth gauge was dropping steadily as the _S-18_ plunged downward through the black waters. From Commander Ford on down, everyone was tense. This was the big test. If anything went wrong-- But they couldn't think of that, that is, no one except Tim who had nothing else to do.