The _NX-1_ swung around, always maintaining a slight forward motion and zigzagging constantly to nullify the heat beam. Wells watched the range-finder closely. The octopi ship slanted downwards, the deadly violet ray stabbing from her bow. Slowly the black dot that represented her appeared on the dial, and slowly it dropped towards the crossed lines that showed the perfect firing point.

Keith grasped the torpedo lever. The _NX-1's_ stern was towards her target. Dead silence hung in the control room. The _NX-1_ swung slightly. The octopi craft appeared directly in the middle of the dial.

Wells pulled back the lever.

The hiss of compressed air sprang from her stern. He had fired two tubes, his whole stock of stern torpedoes. The pair of dreadful weapons leaped out and settled on their course. Keith shot his gaze to the teleview.

The torpedoes missed. Only by feet, but a miss all the same. They raced on past the octopi submarine and, with a tremendous, ear-numbing explosion, burst on the wall of the cavern beyond. Both ships reeled from the shock. Graham swore viciously, but Wells' masklike face showed no slightest change of expression....

A voice rang in Keith's headphones. "Tough, Keith! Better luck next time!" Then the commander winced. He simply could not answer Hemmy Bowman; could not answer that fine, brave voice....

The stern torpedoes were gone. The tubes could not be reloaded, for the paralyzing ray bound the men to the control room. That left them two torpedoes in the bow.

The violet heat ray kept fingering hungrily on their outer hull, and every man knew that the plates were weakening under the steady strain, which was only lessened by the _NX-1's_ constant zigzagging. The control room was very hot. Both ships were now a full mile from the tunnel entrance. Keith plunged the _NX-1_ down, swung her around, to bring his bow tubes to bear, and zigzagged upwards.

It was obvious that the octopi craft had been alarmed by the terrific explosion. They now adopted tactics similar to the American ship's, and for awhile both submarines circled cautiously, maneuvering for an opening.

"If only we could keep the ship steady!" Graham muttered. "But then that heat ray'd get us!"

The commander kept his eyes on the teleview. Again and again the violet shaft p.r.o.nged at them. The heat grew stifling. Sweat was pouring from all the men's bodies. Every face was strained and taut.

"Starboard full!" Wells said suddenly. "A little up, Graham!" He had seen a chance; the octopi craft was slightly above, and in a moment would pa.s.s directly in the line of the bow tubes. The _NX-1_ stuck her nose up, swung rapidly to the right. Keith pulled back the firing lever, releasing one torpedo.

The long messenger of death hurtled straight for the enemy's hull.

They watched its course breathlessly....

"My G.o.d!" the first officer groaned. "Could they see it coming?" For the octopi submarine had swung to one side, neatly dodging the speeding tube of dynamite.

"One left!" he added bitterly. "One left!"

A desperate plan formed in Keith Wells' mind. His last torpedo simply had to strike the mark; he could take no chances with it. He motioned the haggard-faced Graham to him.

"There's only one thing left to do," he said quietly. "We've got to deliberately face that heat ray; chance its puncturing our plates."

"How do you mean, sir?"

"Get in very close, so as to make our last torpedo sure to hit. We've got to approach the enemy head-on at full speed. We'll corkscrew up to them until we get within two hundred yards, then go straight forward for ten or fifteen seconds, giving us the opportunity to sight the remaining torpedo directly on them. The heat ray may break through before I fire--but when I do fire it's a sure hit."

The men had heard every word. Quietly Wells ordered:

"Take the torpedo control, Graham. I'll take the helm."

The first officer obeyed without a word. Keith grasped the helm. The plans were made for their last desperate attempt.

"Right," the commander said shortly. "Here we go."

There had been a taut silence before, but now, knowing that they were deliberately offering themselves a perfect target for the heat ray in order to get their last torpedo home, the intensity was almost unbearable. The men felt like shrieking, jumping--doing anything to break the awful hush. The air was charged with the same unnameable something that heralds a typhoon.

Keith Wells was like a white statue at the helm, save for the betraying trickles of sweat that coursed down his drawn cheeks. His hands moved the wheel slowly from port to starboard; his eyes bored at the screen before him. The ship was in command of a man of steel, a man with but one purpose....

"Up--up," he ordered. "Hold--in trim--full speed forward!"

He had brought the _NX-1_ directly in line with the octopi ship. And now the craft leaped forward under full power, while he shot the helm back and forth ceaselessly. His ship was describing a corks.c.r.e.w.i.n.g motion, weaving straight at the enemy. Grasping her opportunity, the octopi submarine remained motionless, steadily dousing the approaching American craft with her silent violet ray and driving the temperature in the control room to even greater heights.

The distance between them rapidly lessened. Would the plates stand it?

Would the ray melt through the weakened steel before he could fire?

With an effort Keith drove these doubts from his mind ... but he could not banish a certain dull, steady ache from his consciousness....

The range dwindled. The heat became intolerable. Everyone's clothing was sopping wet. A man ripped off his shirt, gasping for air. Wells kept his eyes on the screen, though half-blinded by smarting sweat.

The plates had to give soon, he knew.

The octopi submarine, beam on and dead ahead, began to move to port at quickly increasing speed. At once Keith stopped swinging the helm, and the _NX-1's_ corks.c.r.e.w.i.n.g motion of protection ceased. And then came the real test, the gauntlet of seconds.

Right straight into the retreating violet beam they went, at top speed. They gained rapidly. The heat was furnace-like. The commander, watching the range-finder, kept moving the helm slightly over. A shaft of violet heat spanned the two sh.e.l.ls of metal. For ten seconds it had held on the _NX-1_. The black dot of the enemy craft moved slowly to exact center on the dial. Fifteen seconds ... twenty ...

twenty-three--

"Fire!"

Graham jammed the torpedo lever back.

"Crash dive!"

The deck tilted downward. And Wells' white lips formed the words, "So long, Hemmy!"--and he tore the phones from his head.

Seconds later a t.i.tanic explosion sounded through the cavern; echoed and re-echoed in vasty roars. The American craft's lights went off--but not before her men had seen, in the teleview, a fire-shot maelstrom where a moment before the octopi submarine had been.

"We got them!" yelled Graham.

A roar of exultation burst from every throat. The men flung their arms out, jumped, yelled crazily. Faint emergency lights lit the scene.

"Below, at regular posts," Wells ordered. "Reload bow and stern tubes.

Graham, see to the lights." He himself remained at the helm. In a few moments the submarine had climbed back to the level of the tunnel. At quarter speed she nosed into the wide entrance, and slowly forged into the dense, deceptive shadows.

The commander acted mechanically. Again by touch he steered his ship through the black, ragged cleft. Fifteen minutes after leaving the cavern of the octopi her bow poked through the weaving kelp into the free, salty depths of the Atlantic Ocean.

There was one more task to perform, and Wells lost no time in doing it. When two hundred yards away he halted the _NX-1_, steadied her and sighted the stern tubes just above the dark tunnel hole. Quickly he sent forth two torpedoes.

A huge roar rumbled through the water, whipping the beds of kelp to mad convulsions. "Turn around," the commander ordered harshly. He sighted his bow tubes and again let loose a bolt of two torpedoes.