That on which Darrin now trained his night gla.s.s was a marked rippling on the water, half a mile away, and farther seaward. A landsman would have missed it altogether. Yet that rippling on the sea's surface was clearly different from the motion of the water near by.

"It might be a school of large fish," Dave mused aloud, in Runkle's hearing, "though at night they are likely to rest. Runkle, and you, men, keep your eyes peeled to see if you can make out fish leaping out of the water."

The ripple continued, unbroken at any point. Moreover, it moved at uniform speed, and in a line nearly parallel with the coast.

Gradually the launch gained on that ripple. Dave could not turn his fascinated gaze away from the sight.

"I think I know what that is, sir," broke in Seaman Runkle, after three minutes of watching.

"I am sure that I _do_, Runkle," Dave Darrin returned. "It's a submarine, for some reason just barely submerged. That line of ripple is the wake left by her periscope."

As if to confirm the young naval officer's words, the ripple parted.

As the line on the water broke, the periscope came fully into view, and the turret showed above water, continuing to rise until the deck was awash.

"There's the pest of the seas!" cried an excited voice.

Every man on the launch was now straining his eyes for a better look at the submarine, barely a quarter of a mile away.

CHAPTER XXIII

THE PUZZLE OF THE DEEP

"c.o.xswain!" shouted Dave.

"Aye, aye, sir."

"Send up three blue rockets!"

"Aye, aye, sir."

One after another the rockets ascended, bursting high overhead and slowly falling.

From Grand Harbor, several miles distant, a rocket ascended and burst, showing red.

Darrin's signal had been seen and answered. Both fleets now knew that one of the launches had sighted the submarine craft. The three blue rockets had been the signal agreed upon in advance. Runkle was at the gun. Ensign Darrin gave him the range.

"I wish we had a four-inch gun in the bow," Dave muttered wistfully, "but we'll have to do the best we can with the one-pounder. Ready!

Fire!"

Even before the command to fire had been uttered the craft ahead had begun to submerge.

As the brisk, snappy report of the little piece sounded, and a faint puff of smoke left her muzzle, Runkle's head bobbed up to watch the result of his shot.

"Forward of her turret by about a foot!" Runkle muttered in disgusted criticism of his own shooting.

A sailor had thrown the breech open, while a second swabbed the bore through and the first fitted in a fresh sh.e.l.l, closing the breech with a snap.

Runkle seemed to sight and fire almost in the same instant, and, as before, straightened up to watch the accuracy of his shot by the splash of water on the other side of the craft. The launch's searchlight held a steady glare on the mark.

"Nearer by a few inches, sir," Runkle called over his shoulder while the men with him swabbed and loaded. Again Runkle fired.

"The sh.e.l.l must have pa.s.sed aft of the turret by about six inches,"

remarked Darrin, catching through his gla.s.s a glimpse of the splash of water where the little sh.e.l.l struck the waves.

"I'll do better, or drown myself, sir," growled Runkle.

"Quick! She is submerging rapidly," commanded Darrin.

Bang! An instant after the report a smothered exclamation came from the unhappy gunner. The submarine had safely submerged. Not even her periscope was above water now.

"If the turret had been four inches nearer the sky you'd have put it out of commission," declared Ensign Darrin.

"Rotten work," growled Runkle in disgust.

"It's night shooting, my man," Dave answered. "Good work just the same."

Runkle had an excellent gunnery record, and Darrin did not like to see that fine fellow fretting when he had done his best. None the less it was highly important to send that submarine to the bottom and quickly at that.

"We've got to go by bubbles, now," Darrin declared. "She isn't likely to show her eye again."

Had he gotten the launch close enough to observe the bubbles it is possible that the young ensign could have followed the enemy trail.

Twice or thrice Dave believed that he had picked up glimpses of bubbles with the searchlight, but at last, with a sigh, he gave orders to shut off speed and drift. Inaction became wellnigh insupportable after a few moments and Darrin called for slow speed ahead.

"There she is again" he cried. "There's her periscope. The scoundrel is standing out to sea."

Over the starboard quarter the searchlight signals of two other launches were observed.

"What's taking place?" came the signaled question from one.

"Fired a few shots at a vanishing turret, but missed," Dave ordered signaled back. "Enemy standing out to sea. Am following."

"Will follow also," flashed back the answer.

"And one of their gunners will bag the game at the first chance,"

groaned Runkle. "The jinx is sitting tight on my chest to-night!"

"It might be, if there were any such animal as a jinx," laughed Darrin. "Your missing was just plain bad luck, Runkle. Your shooting was good."

"The periscope is being pulled inboard, sir," called one of the seamen who stood by with Runkle.

"I see it. There she goes, under again," Dave answered.

The Navy launch was dashing full speed ahead. But with no clue to follow, Darrin pa.s.sed some anxious seconds. Should he follow on the course he had been taking, or should he shut off speed? In the dark there was a good chance that the submarine commander, if so minded, would be able to double and head back for sh.o.r.e.