"Why," Dave explained, "a man at laborious physical work uses up more air than a man who is keeping quiet. If the three officers are going to work hard in there then they've closed the door in order not to deprive us of air." "We called them kids, at first," spoke Dan Dalzell ruefully, "but they're a mighty fine lot of real men, those three acting Naval officers." Dave Darrin rose and walked over to the engine room, opening the door and looking in. Hal and Eph were hard at work over the motor, while Lieutenant Jack Benson, with his hand in his pockets, stood watching their efforts. "I beg your pardon, sir," said Darrin, saluting, "but did you close this door in order to leave more air to us?" "Yes," answered Jack Benson. "Go back and sit down." "I hope you won't think us mutinous, sir," Darrin returned steadily, "but we don't want any more than our share of whatever air is left on board this craft. We belong to the Navy, too." From the after end of the cabin came an approving grunt. It was here that the cook and the four seamen had gathered. With the door open the midshipmen could see what was going on forward, and they watched with intense fascination. Eph Somers had taken 'the too-thin copper' plate to the work-bench, and had worked hard over it, trying to devise some way of making it fit so that it would perform its function in the motor. Now, he and Hal Hastings struggled and contrived with it. Every time that the pair of submarine boys thought they had the motor possibly ready to run Hal tried to start the motor. Yet he just as often failed to get a single movement from the mechanism. "I reckon you might about as well give it up," remarked Lieutenant Jack Benson coolly. "What's the use of giving up," Eph demanded, "as long as there's any life left in us?" "I mean," the young lieutenant explained, "that you'd better give up this particular attempt and make a try at something else." "All right, if you see anything else that we can do," proposed Eph dryly. "Say, here's a quarter to pay for your idea." Seemingly as full of mischief as ever, Eph Somers pressed a silver coin into Jack Benson's hand. But Jack, plainly impatient with such trifling, frowned slightly as he turned and pitched the quarter forward. "This isn't a twenty-five-cent proposition," Benson remarked. "In fact, all the money on earth won't save us this time!" CHAPTER XI A QUARTER'S WORTH OF HOPE "Until some one can think of something else, I'm going to keep on trying the hopeless thing and endeavoring to make this old, thin plate work," declared Hal Hastings, who was still bent over the motor, studying it intently. Benson had turned back to examine the work, after tossing the coin away, but just as suddenly he glanced forward again.