“Light ahead?” echoed the officer, springing to his feet. The others followed his example. Up the steel ladder sprang Lieutenant Parry, followed by the rest. Curious faces poked out of the engine room to ascertain the cause of this sudden exodus.

Up in the conning-tower it was easy enough to see the light that had attracted Sim’s attention. It was an immensely bright light, high up. Below it were two sailing lights, red and green.

“Jove!” exclaimed Lieutenant Parry, “that’s a navy craft. See that large, intensely bright masthead light? That’s the night insignia of one of Uncle Sam’s ships.”

“Let’s give her a hail, sir,” suggested Midshipman Stark; “in a way, we, too, are a naval craft now.”

“Wonder what ship she is?” mused Lieutenant Parry, paying no attention to this suggestion. “I have it,” he exclaimed the next minute. “It’s the gunboat Brooklyn. I recollect she was ordered to Boston last week. She’s going up through the Sound.”

Midshipman Stark repeated his suggestion.

“That’s a good idea, Stark,” said the officer; “her commander, Lieutenant-Commander Scott, is an old friend of mine. Wouldn’t he be astonished to know that we were so close to him! Why, in time of war, if his was a hostile ship, all we would have to do would be to dive, and then torpedo him.”

“I believe we could even creep up and board him without his noticing us,” put in Mr. Lockyer, gazing at the bright light which was now almost abeam of them.

“By George! Do you really think so, Lockyer? Wouldn’t that be a prime joke? But how could we do it?”

Nobody had any suggestions to make till Ned spoke up.

“I think I could suggest a way, sir,” he said quietly.

“Let’s hear it, Strong,” eagerly exclaimed the officer. “If we could carry such a thing out it would be a good joke in navy circles for a long time to come.”

“All the apparatus it would need, sir, would be some line and a heavy weight.”

“A sounding lead?” asked Mr. Lockyer.

“Yes, sir. Have you any on board?” asked Ned.

“Several, and plenty of line, too. But now let’s hear your plan.”

They eagerly listened while Ned detailed his scheme to give Lieutenant-Commander Scott an unexpected visit in mid-Sound. As he unfolded it, his hearers grew more and more enthusiastic.

“Splendid. We’ll do it if you are agreeable, Mr. Lockyer,” said the officer.

“Anything that will test the capabilities of the Lockyer boat I am agreeable to—nay, anxious to see tried,” was the rejoinder.

“Very well, then. Now, lad”—to Sim, who was steering—“ring for full speed and get us ahead of that gunboat. Better run with the turret awash, so that she won’t see us if they should take a sudden fancy to have some searchlight practice.”

A perceptible increase in the speed came almost immediately following the signal. At the same time, the machinery for submerging the craft was put in operation, till the conning-tower was almost completely under water. The clamps were tightly screwed, so that in case it became necessary to make a sudden dive it could be done instantly.

A perfect knowledge of the gunboat’s whereabouts were had, even under water, by use of the periscope. This necessary part of every submarine’s equipment is a simple variation on the old camera obscura. A long tube, with a mirror at the top, projected above the surface of the water. It offers no more target than would the slender neck of a floating bottle, and would hardly attract any attention. Inside the tube are other mirrors, so arranged as to reflect a perfect picture of the waters above, upon a flat, white surface—something like the top of a desk—set in front of the helmsman in the conning-tower.

Of course, as it was at night, all that could be seen in the periscope reflector was the bright light on the gunboat’s masthead, but this served quite as well to locate her as if it had been daytime, and they could have seen the reflection of her whole outline.

They speedily drew ahead of the gunboat, which was not, apparently, making more than ten or twelve knots. Forging steadily forward, the submarine was maneuvered till she was directly across the gunboat’s bows, but some distance ahead.

“Is this about far enough, Strong, do you think?” asked Lieutenant Parry.

“I think so, sir,” nodded Ned gravely, “and now, if you think everything is ready for it, we’ll give them a whistle.”

“Go ahead,” nodded the officer.

Ned seized the compressed-air whistle’s lever and sent an eerie scream out over the waters. As its echoes died out they could see a sudden ray of light shoot upward from the dark form of the gunboat, as reflected in the periscope.

“They’ve heard the whistle, and are wondering what it is. There goes the searchlight!” cried Lieutenant Parry, as the fan-shaped ray hovered about for an instant, and then began to sweep the waters. “Dive quick, before they pick us up.”

Ned sprang to the wheel and jerked over the sinking controls. Instantly the little of the submarine that showed above the surface was completely submerged.

“How much does she draw, sir?” asked Ned, turning to the officer.

“About fifteen feet, I guess,” was the rejoinder.

“Then I’ll sink to twenty-five, sir, and come up as near astern as I can.”

Down they dropped, till the gauge showed that they were twenty-four feet under the surface. Ned brought the craft on an even keel, and then began the ascent. As they rose to the surface, every one in the conning-tower gave a cry of surprise. So accurately had the Dreadnought Boy gauged the distance that the Lockyer came to the top not more than ten feet astern of the gunboat. They could see her big counter looming up blackly against the starry sky.

Forward, the searchlight was sweeping the waters in every direction. Evidently, that sudden whistle from dead ahead had got on the nerves of those in charge of her navigation.

“My, but they must be a sadly puzzled crew on board the Brooklyn,” chuckled Lieutenant Parry.

The others were scarcely less amused at the way in which the larger vessel was helplessly sweeping the waters in search of the mysterious cause of the alarm.

“I saw a bear once, back in the Catskills, that had been stung by a bee,” whispered Herc; “the way that old gunboat is carrying on reminds me of it.”

“Will there be any one astern, sir?” asked Ned of Lieutenant Parry, the next minute.

“Should be a marine sentry by the illuminating buoy, but I guess they’re all forward, trying to find out if they’ve run down anything,” whispered back the lieutenant; “but we’ve got to act quickly if we are to act at all.”

“Very well, then, sir,” rejoined the young boatswain’s mate, throwing back the conning-tower top without making the slightest noise. “Mr. Lockyer, will you hand me up that line, sir, and one of the weights?”

The inventor passed up to the lad a coil of stout, half-inch rope, to the end of which Ned rapidly attached one of the heavy sounding leads.

“Now then, sir, if we can creep up under her counter, I can do the trick,” he whispered, when this had been done.

Silently, the little sea-tiger crept in under the shadow of the gunboat’s overhanging stern. Ned took good aim, and holding a coil of the rope in one hand—like a cowboy about to throw a lariat—he hurled the lead upward. It swished round the gunboat’s stern jackstaff, in which a boxed stern-light was burning, and fell on the other side, having carried the rope to which it was attached round the staff.

For an instant they held their breath. From forward there came a sudden tinkling sound.

“Ding-ding, ding-ding!”

“Fow-er bells, and all’s well!” came the cry from the bow, ringing weirdly out on the still air.

“Wait a jiffy,” breathed Lieutenant Parry. For an instant they waited in suspense. Then came an answering cry from the stern.

“All’s well.”

“Good. That sentry was off his post, as I thought, while we were creeping up,” whispered the officer; “now then, Strong, are you ready?”

“As soon as I’ve made the end of the rope fast, sir,” was the reply, as Ned rapidly took a half-hitch with the loose end about a cleat on the deck. This done, he made fast the other end to another cleat on the side of the conning-tower. The submarine was now practically in tow of the Brooklyn, the looped rope about the jackstaff holding the two vessels together.

Ned slipped off his shoes, and then cast his coat back into the conning-tower. In the meantime, Lieutenant Parry had stooped low, and tearing a page out of his note-book, had rapidly written something in the light from the periscope binnacle.

He folded the paper and handed it to Ned.

“Good luck!” he whispered, thrusting it into the lad’s hand.

“Thank you, sir,” rejoined Ned briefly.

Then, with the note thrust into his shirt, he ran forward, and began clambering up the ropes. It was no trick at all for the nimble, hard-muscled lad to gain the afterdeck of the gunboat. His progress was eagerly watched until the curve of the counter shut him out from view.

“Oh, but won’t there be fireworks in a while,” chortled Midshipman Stark, doubling up with mirth.

“Hush, Stark,” admonished the lieutenant. “Listen!”

From above there came the sharp ring of a musket butt, and then an astonished hail.

“Halt! Who goes there?”

“That’s the sentry. Strong’s on deck all right,” whispered Lieutenant Parry. Then, in Ned’s voice, there came from above:

“A messenger from the deep sea. I have a message for Lieutenant-Commander Scott.”

“The explosion is due in about five minutes, Lockyer,” chuckled the naval officer blithely. “Oh, won’t Scott be in a fury,—and he always declared that submarines were useless in practical warfare.”