arine, 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_ corkscrewing 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 shells 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 titanic 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.
Then he sent the submarine forward, and, through the teleview,
examined what his four weapons had done.

Huge chunks of rock had b