To attempt to open it would probably jeopardize the safety of the vessel, and Hythe was too good a sailor to tamper with the securing bars.

"Might have known that," he growled. "Now, what's to be done."

Another thud, this time to starboard, made the "Aphrodite" tremble again, but there was no disconcerting heel following the shock. Hythe had no doubt about it; the concussions were caused by explosions, either of torpedoes or floating mines, outside the vessel.

"I wonder how many of these she'll stand?" he muttered, clambering up three or four rungs of a ladder and trying a manhole above his head.

"Well, here goes. I'll try this hatchway. The cover isn't locked."

Back slid the metal slab, and the sub saw that he had opened a means of communication with the after conning-tower. The place was in semi-darkness, only the subdued light from the pale green water filtering in through the observation scuttles. As the electric-light from the alley-way flashed upwards one of the occupants of the conning-tower glanced down and gave an exclamation of annoyance, adding:--

"Hurry up and cover that hatchway. How can you expect me to see ahead with that glare under my eyes?"

"Sorry, Devoran," replied the sub, hastily skipping up the remaining portion of the ladder and replacing the cover.

"Oh, it's you, is it?" said the chief officer. "Sorry, I thought it was Polglaze. Can't talk now. Stand here, if you will."

Devoran indicated a place on his left, so that Hythe could see out of the for'ard and port scuttles. It was some time before his eyes grew accustomed to the half-light; then by degrees he saw that the "Aphrodite" was tearing through the water at a great speed. A hundred feet in front of him he could discern the fore-conning-tower, and beyond that nothing but water that faded into extensive gloom. No sign of the "Vorwartz" was to be seen.

Hythe stood and waited. Without doubt the "Aphrodite" was in chase of the rival submarine, so that the latter had attempted strong measures to beat off her pursuer, but the absence of anything to be seen came somewhat like a disappointment to the young naval officer.

Suddenly there was a wild disturbance in the water less than twenty yards abeam. Again the sickening concussion even more noticeable within the conning-tower than down below.

"Torpedo!" e.j.a.c.u.l.a.t.ed Devoran. He had no time for further explanation, and Hythe was at a loss to understand how the dangerous missile had exploded without actually coming into contact with the metal plating of the submarine.

"What's that, by smoke!" e.j.a.c.u.l.a.t.ed the chief officer, as in place of the almost inaudible purr of the motors came a most discordant clanging, jawing, and groaning of machinery, while by observing the compa.s.s Hythe saw that the "Aphrodite" was describing a wide circle to starboard.

"You've buckled one of your propeller shaftings," said the sub. "I've had some before. I know what those noises mean."

"I hope not, by Jove!" replied Devoran, and almost at that moment the telephone bell operator from the motor room rang. "You're right,"

continued the chief officer. "It is the propeller shaft; we're knocked out for the time being."

Captain Restronguet remained in the fore conning-tower till the indicator of the detector showed that the "Vorwartz" had put a safe distance between her and her pursuer; then leaving the course in the hands of a quartermaster, he gave orders for the "Aphrodite" to be brought to the surface.

Hythe would have forborne to question the captain at such an anxious time, but to the former's surprise Captain Restronguet hailed him quite genially and in a manner that showed no trace of his annoyance at being temporarily baffled.

"Well, Mr. Hythe, wherever have you been?" he asked. "I thought you were following me when I left the cabin, and never missed you till ten minutes ago. You see, I had to keep all my attention on what was going on."

"You said nothing about my accompanying you, sir," replied the sub. "As a matter of fact I took the liberty of going up into the after conning-tower."

"That was better than remaining below," agreed Captain Restronguet.

"Only there was not so much to be seen. From the for'ard tower we caught sight of the 'Vorwartz' on two occasions."

"I should have thought you had her in sight the whole time, sir,"

remarked Hythe. "Otherwise I cannot see how you kept in her track."

"By means of the detectors. I can fix the position of the 'Vorwartz' to a nicety, and no doubt that scoundrel of a von Harburg can do the same, thanks to my invention, of which he basely availed himself. I suppose you know he let loose four torpedoes?"

"Yes; but it puzzled me to know why they exploded so far from the ship."

"The 'Aphrodite' can, when desired, be protected by a belt, as it were, of electric fluid, so long as she remains under water. Any explosion brought within that zone would be spontaneously ignited. It was a weak current that knocked all the stuffing out of you, when you were nearly run down at Spithead."

"Then, this submarine is practically invulnerable?"

"When submerged, yes. A mine or a torpedo cannot harm her, and at a depth of fifty feet she is out of all danger of being run down. On the surface she might, if perceived, be a target for a quick-firing gun, or she might be cut in two by a large, swiftly-moving steamer. Von Harburg, did he but know it, has a unique opportunity now our propeller shafting is gone; he might wait till we rose to the surface and then ram us."

"But why didn't you torpedo his 'Vorwartz'?" asked Hythe. "Your torpedoes would easily overtake that vessel."

"It was in my power to do so," replied Captain Restronguet calmly. "But I refuse to do so in the interests of humanity. It is part of my creed that human life is sacred, and should not be sacrificed unless absolutely necessary."

"But you vowed you would destroy the 'Vorwartz'?"

"Most certainly. What I wanted to do, and what I will, I hope, eventually be able to do, is to play with that wretched counterfeit of my submarine, and drive von Harburg into a state of panic. Then as soon as I can pursue the 'Vorwartz' into comparatively shallow water I will sink her--but if humanly possible, I will save her crew. Come on deck, Mr. Hythe. You will then be able to see how we tackle repairs of this description."

The sub followed his host on deck, where about half of the crew were engaged in rigging up a pair of sheer-legs over the stern. At the same time the water ballast was being ejected from the ballast tanks in the sternmost section of the vessel, while the bow compartment tanks correspondingly filled.

Lower and lower sank the for'ard portion of the "Aphrodite," while the after end rose out of the water till the blades of the polished propellers were exposed to view. From the head of the sheer-legs a double block was fixed, the tackle being brought to bear upon the damaged shafting.

"We're in luck, sir," shouted Kenwyn, who had lowered himself over the stern. "The metal is not fractured; it's a length of tarred rope wound round and round the boss of the propeller."

"Take axes and cut the rope through," ordered Captain Restronguet, addressing Carclew and Gwennap. "We'll soon clear that."

Hythe was not so sanguine. He had known rope to baffle the efforts of half a dozen men working for two hours in a similar case, for the strain is so great that the entanglement is compressed into a solid ma.s.s almost as hard as steel.

"Might I suggest a hack-saw?" he said. "That will do better, since there is less danger of harming the metal than with an axe. If you have no objection, sir, I will bear a hand."

"Certainly," replied Captain Restronguet.

Glad of an opportunity of doing something the sub borrowed a working suit, and with a bowline under his arms was lowered over the stern, where the two men were already astride the propeller brackets.

Hitherto the sea had been fairly calm, but with provoking suddenness the wind piped up, and vicious little wavelets began to splash over the energetic toilers. Desperately they hacked at the stubborn rope, removing the coils piece-meal. Higher and higher rose the waves, till the work became hazardous.

"Pa.s.s me that long marline-spike, Gwennap," exclaimed Hythe. The man leant forward with the pointed piece of steel in his hand. As he did so a sea swept over him; he dropped the marline-spike and grabbed frantically at one blade of the propeller; missed it, and the next instant was struggling in the sea.

[Ill.u.s.tration: "HE GRABBED FRANTICALLY AT ONE BLADE OF THE PROPELLER."]

One glance sufficed to show the sub that the unfortunate man could not swim a stroke. However competent he was underneath the sea in his diver's dress it was a certainty that he was absolutely helpless when it came to keeping on the surface. He raised his hands above his head, and in consequence sank. By the time he came to the surface again, the submarine, now light and high in the water, had been blown ten yards astern. The officers and men on deck were all equipped in heavy working-suits and sea-boots, while the dinghy, the only above-water life-saving appliance on board, was down below. There was not even a rope handy that was long enough.

Captain Restronguet, Devoran, and several others were struggling to cast off their c.u.mbersome clothing and boots, but they were too late, for Hythe, slipping out of the bowline, dived into the water. Although more than fully clad, since he had donned overalls over his uniform, he fortunately was not wearing sea boots.

Striking out vigorously he gained the spot where Gwennap had sunk just as the man appeared for the second time. Bearing in mind the instructions laid down in official directions for saving life Hythe used a fair amount of precious breath in bawling in a loud voice that the drowning man was safe. Gripping Gwennap by the collar he jerked him on to his back, the man struggling furiously the while. Hythe, realizing that once the frantic and powerful fellow gripped him, it would be "all up," had his work cut out to avoid the man's arms. One glance showed him that the "Aphrodite" was drifting fairly fast to leeward; his a.s.surance that the drowning man was safe seemed a hollow mockery.

"Don't struggle, you idiot!" spluttered Hythe, as the crest of a wave broke over his head. "Don't you see you'll do for the pair of us?"

But Gwennap evidently did not see, for if anything he struggled the more.

The sub came to the conclusion that the situation was a desperate one.

He was rapidly becoming weaker; his clothes, now thoroughly waterlogged, seemed like leaden weights. He had lost all sense of direction; he knew not where the "Aphrodite" lay. It seemed as if he were left with a frantic, drowning man in the lone sea. But not for one moment did Hythe intend to abandon the man he had so gallantly attempted to rescue. If only he could prevail on Gwennap to keep fairly still a chance yet remained; but the man showed no signs of ceasing to struggle.

"Let go!" shouted Hythe, as loudly as he could, as Gwennap's huge fist seized him by the shoulder, followed by an iron grip on his coat-sleeve.