In the darkened room in the bow of the vessel, with the powerful searchlight lighting up the murky water ahead, Frank kept careful vigil. Hour after hour he sat there in silence, hardly moving from his first position. The D-16 forged ahead but slowly, for there was no need of undue haste and Lord Hastings was not minded to take unnecessary chances. Frank glanced at his watch. "Midnight," he muttered to himself. "Only one more hour and then I can turn in for the night." Still the minutes passed without incident. Finally, at a few minutes to one, Frank, after a second glance at his watch, arose and stretched himself. "Guess nothing will turn up in my watch," he told himself. But the lad was mistaken. For one moment he had taken his eyes from the water ahead, and now, glancing forth once more, he beheld a sight that moved him to instant action. His eyes fell upon a large object directly ahead, a scant hundred yards. Quickly the lad jumped to the bell that signalled the engine room. And almost as quickly the speed of the vessel was checked. But the nose of the submarine was now but inches from the dark looking object ahead. Lord Hastings' face appeared in the room. "What's the matter?" he demanded. "Looks like a mine, sir," replied Frank quietly. Lord Hastings advanced until he could get a good look at the object. He peered at it long and carefully, then turned to the lad. "You are right," he said. "It is a mine. Had you perceived it an instant later we undoubtedly would be in the land of the missing by this time." Frank flushed at this, for he realized perfectly that had he been paying strict attention to his duties, the submarine would not have come this close to danger of destruction. But he said nothing. The mine extended well up toward the surface of the water, but the bottom of it was in plain sight. "I suppose the best thing to do is to dive under it," said Lord Hastings. "My idea, too, sir," agreed Frank. Lord Hastings turned on his heel and left the compartment, and a moment later the vessel began to sink lower and lower into the sea. Frank still stood on watch, and when he was certain that the D-16 would pass beneath the mine without danger of striking it, he gave the signal and the vessel headed forward once more. Lord Hastings entered the compartment again. "The chances are there are more of them," he said, "so we shall have to be very careful. I'll have Mr. Templeton take the next watch, for we cannot keep too sharp a lookout." Frank nodded his head in assent. Lord Hastings left. Five minutes later Jack appeared at Frank's side and the latter turned to go. Suddenly he whirled about and spoke to his chum. "You must be more careful than I was," he said quietly. "I was almost the means of sending us all to the bottom for good." "What do you mean?" asked Jack in surprise. Frank explained. "Well," said his chum consolingly, "a miss is as good as a mile, you know."