water with undiminished speed,
but the precaution was needless--Nerado knew thoroughly his vessel, its
strength and its capabilities. There was a mighty splash, but that was
all. The artificial gravity was unchanged by the impact; to the
passengers the vessel was still motionless and on even keel as, now a
submarine, she snapped around like a very fish and attacked the rear of
the nearest fortress.

For fortresses they were; vast structures of green metal, plowing
forward implacably upon immense caterpillar treads. And as they crawled
they destroyed, and Costigan, exploring the strange submarine with his
visiray beam, watched and marveled. For the fortresses were full of
water; water artificially cooled and aerated, entirely separate from the
boiling flood through which they moved. They were manned by fish some
five feet in length. Fish with huge, goggling eyes; fish plentifully
equipped with long, armlike tentacles; fish poised before control panels
or darting about intent upon their various duties. Fish with intelligent
brains, waging desperate war upon a hated foe!

Nor was their warfare ineffectual. Their heat-rays boiled the water for
hundreds of yards before them and their torpedoes were exploding against
the Nevian defenses in one appallingly continuous concussion. But most
potent of all was a weapon unknown to Triplanetary warfare. From a
fortress there would shoot out, with the speed of a meteor, a long,
jointed, telescopic rod, tipped with a tiny, brilliantly shining ball.
Whenever this glowing tip encountered any obstacle, that obstacle
disappeared in an explosion world-wracking in its intensity. Then what
was left of the rod, dark now, would be retracted into the
fortress--only to emerge again in a moment with a tip once more shining
and potent.

Nerado, apparently as unfamiliar with the peculiar weapon as were the
Terrestrials, attacked cautiously; sending out far to the fore his
murkily impenetrable screens of red. But the submarine was entirely
non-ferrous, and its officers were apparently quite familiar with the
Nevian beams which licked at and clung to the green walls in impotent
fury. Through the red veil came stabbing tiny ball after brilliant ball,
and only the most frantic dodging saved the space-ship from destruction
in those first few furious seconds. And now the Nevian defenders of the
Third City had secured and were employing the vast store of allotropic
iron so opportunely delivered by Nera