The gallant lads in the engine-room were doing their best. A shell from long range, with most of its force expended, glanced off the port bow of the submarine, carrying away the towing pennant. The nose of the Y-3 ducked under a bit, but came up serenely in half a second. The commander of the vessel, perceiving deep water ahead, encouraged the helmsman with a cry. Already the vessel was almost over the bar. The fire from the fort was decreasing. Only the longer range guns could come into play now. Looking back, the lads saw two destroyers racing in the wake of the submarine, preceded by a small gunboat. The first shells of the gunboat whizzed by the submarine. Captain Nicholson slammed down the hatch. "Water armor for us!" he cried. A moment later the submarine was on the safe haven of the bottom with 100 feet of solid protecting water between it and hostile shells. "That was pretty ticklish," said Frank, drawing a breath when they were out of reach of the gunboat's fire. "It was," was the commander's response, "and we are not safe yet by any means." "Why--?" began Frank. "We can't go up again now, can we?" demanded Captain Nicholson. "We shall have to stay down here until they believe we have escaped. Then we will rise and try to sneak out." "But surely we are safe enough down here." "Don't you believe it. They'll trawl for us all day; but luckily for us they don't know we have lost our batteries, so they'll probably search over a wide area, and we run that much more chance of not being discovered." "But surely no shell would reach us here," said Frank. "No," replied the commander grimly, "but if they discover us, they are likely to dump a few barge loads of pig iron or something down on us and crush our steel plating." But the submarine was not discovered by the enemy and remained below the water all the rest of the day "went to sleep on the bottom," as the phrase goes. And that is what literally was done, for all on board were tired out. An hour after sunset, the Y-3 came once more to the surface. There was no sign of an enemy. The sky was still banked with heavy clouds, and there was a choppy sea running. Captain Nicholson started to run for safety at full speed ahead. Having no batteries for submerged running now, the Y-3 had to remain on top of the water, or else sink to the bottom and lie still; and for this reason Captain Nicholson kept prepared for a quick submersion. Mines were the worst dangers the Y-3 bad to encounter now, and a careful watch was kept and the speed of the vessel reduced. Twice the vessel was picked up by the searchlight on the fort, and each time submerged. But the engines stood up well, and at last Captain Nicholson said quietly to the two lads: "Well, we're safe at last." "Good," said Frank, "but I wouldn't have missed this experience for a fortune." "Nor I," declared Frank.