It was now more than twelve hours since the _Dewey_ had submerged after the exciting events of the preceding night and the air supply was still sufficiently impregnated with oxygen to enable the imprisoned crew to breathe free and normally. The boys knew that the _Dewey_ could continue thus for at least thirty-six hours before her officers would commence drawing on the reserve oxygen tanks. In an atmosphere of suspense the long afternoon dragged into evening. Every effort to free the vessel had been tried, but to no avail. Evening mess was served amid an oppressive silence varied only by the valiant efforts of bluff Bill Witt to stir a bit of confidence in his mates. Another and final effort to get away was to be tried at midnight with high tide. And then---if nothing availed---the boys knew full well that with the morning Lieutenant McClure would resort to some drastic measures. Efforts at sleep were futile for the most part, although dauntless spirits like Bill Witt and Mike Mowrey turned in as usual and dozed away as peacefully as though no danger existed. Midnight and high tide kindled fresh hopes as "Little Mack" steeled himself for a last try with the _Dewey's_ hardworked engines. Jack and Ted had spent the long evening in the wireless room with Sammy Smith, hearing not so much as a trace of a passing vessel. Eagerly they awaited the last herculean effort for freedom. At ten minutes to one the engines were set in motion again and the signal given to back away as before. Lieutenant McClure had resorted to the expedient of shifting everything movable within the _Dewey_ to the bow bulkhead in the hope that the submarine might be tilted forward at the supreme moment. Now he ordered every man aboard ship, except the engineering force necessary to operate the engines, into the torpedo chamber forward. "Whirr-r-r!" the roar of machinery reverberated throughout the hold. The _Dewey_ struggled again in mad convulsion---but all to no avail. The shifted cargo of humans and equipment made no difference; the submersible remained fast. There now was no doubt of the _Dewey's_ serious dilemma. No spoken word was necessary to impress upon the men the critical situation. Sleep was out of the question. Jack rambled into the wireless room, where he tried to calm his restless spirits by rattling away on the key at the code alphabet. Lately he had been giving much attention to mastering the operation of the wireless apparatus and under the direction of Sammy Smith had been making excellent progress. He nervously fitted the microphone receivers to his ears---and the next moment sat bolt upright. He was startled to hear the clicking sound in the listeners that indicated the proximity of a moving vessel. "Quick! Listen here!" he called out to Sammy Smith. The wireless chief dashed down the receivers and hurried to find Lieutenant Mcclure.