more efficient spacedrives to do away with the costly and tedious
manoeuverings required for travel even among the inner planets.

Work of such importance, of course, was supposed to be carried out
only under close guard and under the direct supervision of reliable
upper-echelon scientists of the Machine. Even allowing for criminal
negligence, the fact that the Mars Convicts were able to develop and
test their stardrive under such circumstances without being detected
suggested that it could not be a complicated device. They did, at any
rate, develop it, armed themselves and the miners of the other penal
settlements and overwhelmed their guards in surprise attack. When the
next ship arrived from Earth, two giant ore carriers and a number of
smaller guard ships had been outfitted with the drive, and the Mars
Convicts had disappeared in them. Their speed was such that only the
faintest and briefest of disturbances had been registered on the
tracking screens of space stations near Mars, the cause of which
remained unsuspected until the news came out.

Anything which could have thrown any light on the nature of the drive
naturally had been destroyed by the deserters before they left; and
the few Machine scientists who had survived the fighting were unable
to provide information though they were questioned intensively for
several years before being executed. What it added up to was that some
eighteen thousand sworn enemies of the Machine had disappeared into
space, equipped with an instrument of unknown type which plainly could
be turned into one of the deadliest of all known weapons.

The superb organization of the Machine swung into action instantly to
meet the threat, though the situation became complicated by the fact
that rumors of the manner in which the Mars Convicts had disappeared
filtered out to the politically dissatisfied on Earth and set off an
unprecedented series of local uprisings which took over a decade to
quell. In spite of such difficulties, the planet's economy was geared
over to the new task; and presently defenses were devised and being
constructed which would stop missiles arriving at speeds greater than
that of light. Simultaneously, the greatest research project in
history had begun to investigate the possibilities of either
duplicating the fantastic drive some scientific minds on Mars had come
upon--chiefly, it was concluded, by an improbable stroke of good
luck--or of matching its effects throug