"I have not yet made an exhaustive test of that," rejoined Mr. Barr, "but I estimate that we could remain below, if necessary, forty-eight hours." "Forty-eight hours!" gasped Rob incredulously. The inventor nodded calmly. "My air purifying device makes this supposable. I have a plan by which fresh, pure air is almost manufactured. At the same time the foul air is forced out." "I suppose you boys are aching to take a trip," laughed Ensign Hargreaves. "Aching is no word for it," Rob assured him. "Well, you may have a chance to-morrow," said Mr. Barr; "I am going to test out the whole craft thoroughly, and you boys can come along if I go." For the next five minutes nothing could be heard but enthusiastic shouts. The boys fairly went wild with delight at the prospect of a trip below the ocean's surface. Soon afterward the party emerged from the submarine in time to see the _Seneca_ making out to sea on her return journey. She carried letters from the boys to their families, as they were by no means sure when they would get the next opportunity of sending a letter north. The next hour was occupied in making camp. Then the Stars and Stripes and the Eagle banner went up. Donald had no Wolf banner with him, but above his tent he hung up something that resembled a wolf's head, painted on a bit of canvas. "Looks more like a chicken than a wolf," scornfully sniffed Tubby when he saw it. "You couldn't think of anything but something good to eat, could you?" was Donald's crushing reply. By the time camp had been made and everything placed neatly in order, Andy Bowles, on Ensign Hargreaves' order, sounded the dinner call. "That's the call that Tubby never forgets," laughed Rob, as the stout lad cantered off in the direction of the combination dining hall and cook house above mentioned. They found a bare, pine table, scrubbed scrupulously clean and set with metal plates and cups. Lieutenant Hargreaves showed each boy to his seat, while he and the inventor sat at opposite ends of the board. The sailors, and the machinist who had impressed Rob so unfavorably, ate later. The cook, a stout, good-natured looking negro, came bustling in with a huge bucket-like pan full of steaming soup. Tubby's eyes glistened as he saw it, and soon he was piling in prodigious quantities of it. The soup was followed by salt beef, potatoes, and other vegetables, and then came a big wedge of cocoanut pie. "We get fresh meat fairly often," explained Mr. Barr, "but the launch has not been to the mainland recently, so we have to get along on what sailors call 'Willie'." "Isn't there game of any kind hereabouts?" asked Rob. "Oh, yes. There are several shore birds of different varieties, but we have really been too busy of late to go after them. Now that you boys have come, however, you can take out my shot guns--I have three of them--and see what you can do as hunters." "Are the shore birds good eating?" inquired Tubby with his mouth full of pie.