do.

From the city there pushed out immense nets of metal, extending from the
surface of the ocean to its bottom; nets radiating such terrific forces
that the very water itself was beaten back and stood motionless in
vertical, glassy walls. Torpedoes were futile against that wall of
energy. The most fiercely driven rays of the fishes flamed incandescent
against it, in vain. Even the incredible violence of a concentration of
every available force-ball against one point could not break through. At
that unimaginable explosion water was hurled for miles. The bed of the
ocean was not only exposed, but in it there was blown a crater at whose
dimensions the Terrestrials dared not even guess. The crawling
fortresses themselves were thrown backward violently and the very world
was rocked to its core by the concussion, but that iron-driven wall
held. The massive nets swayed and gave back, and tidal waves hurled
their mountainously destructive masses through the Third City, but the
mighty barrier remained intact. And Nerado, still attacking two of the
powerful tanks with his every weapon, was still dodging those flashing
balls charged with the quintessence of destruction. The fishes could not
see through the sub-ethereal veil, but all the rod-gunners of the two
fortresses were combing it thoroughly with ever-lengthening,
ever-thrusting rods, in a desperate attempt to wipe out the new and
apparently all-powerful Nevian submarine, whose sheer power was slowly
but inexorably crushing even their gigantic walls.

"Well, I think that right now's the best chance we'll ever have of doing
something for ourselves." Costigan turned away from the absorbing scenes
pictured upon the visiplate and faced his two companions.

"But what can we possibly do?" asked Clio, and

"Whatever it is, we'll try it!" Bradley exclaimed.

"Anything's better than staying here and letting them analyze us--no
telling what they'd do to us," Costigan went on. "I know a lot more
about things than they think I do. They never did catch me using my
spy-ray--it's on an awfully narrow beam, you know, and uses almost no
power at all--so I've been able to dope out quite a lot of stuff. I can
open most of their locks, and I know how to run their small boats. This
battle, fantastic as it is, is deadly stuff, and it isn't one-sided, by
any means, either, so that every one of them, from Nerado down, seems to
be on emergency duty. There are no guards watching us, or stationed