Security men at every doorway, moving continually about.

But it still didn't look too good. There is apparently no way to beat
arithmetic, and a definitely grim problem still remained. Ten days after
the beginning of the new construction program, Joe and Sally looked down
from a gallery high up in the outward-curving wall of the Shed. Acres of
dark flooring lay beneath them. There was a spiral ramp that wound round
and round between the twin skins of the fifty-story-high dome. It led
finally to the Communications Room at the very top of the Shed itself.

Where Joe and Sally looked down, the floor was 300 feet below. Welding
arcs glittered. Rivet guns chattered. Trucks came in the doorways with
materials, and there was already a gleaming row of eighty-foot hulls.
There were eleven of them already uncovered, and small trucks ran up to
their sides to feed the fitting-out crews such items as air tanks and
gyro assemblies and steering rocket piping and motors, and short wave
communicators and control boards. Exit doors were being fitted. The last
two hulls to be uncovered were being inspected with portable x-ray
outfits, in search of flaws. And there were still other ungainly white
molds, which were other hulls in process of formation--the metal still
pouring into the molds in powder form, or being tamped down, or being
sintered to solidity.

Joe leaned on the gallery-railing and said unhappily, "I can't help
worrying, even though the Platform hasn't been shot at since we landed."

That wasn't an expression of what he was thinking. He was thinking about
matters the enemies of the Platform would have liked to know about.
Sally knew these matters too. But top secret information isn't talked
about by the people who know it, unless they are actively at work on it.