se of
energy, and the source of the power." Arcot puffed on his pipe
meditatively for several moments, then stood up and stretched.

"Ho--I wish they'd let me go on active duty with the space fleet! A
scientific reputation can be an awful handicap at times," he grinned. He
had been rejected very emphatically when he had tried to enlist. The
Interplanetary governments had stated flatly that he was too important
as a scientist to be risked as a pilot of a space ship.

On two worlds the great construction plants were humming with activity.
Civilian production of all but the barest essentials had been put aside
for the duration of the emergency. Space ships were being turned out at
top speed, getting their fuel from the wrecks of the invaders' cruisers.
Each ship needed only a small amount of the light-metal, for the energy
content was tremendous. And those ships had been gigantic.

Already there was a fleet of speedsters and mother ships out there in
space, and with every passing hour others left the home planets, always
adding to the fighting force that was to engage the attackers deep in
space, where no stray ships might filter through to destroy the cities
of Earth or Venus. Assembly lines were now turning out ships so rapidly
that the training of their operators was the most serious problem. This
difficulty had finally been overcome by a very abbreviated training
course in the actual manipulation of the controls on the home planets,
and subsequent training as the squadrons raced on their outward courses.

It was soon decided that there must be another service beside that of
the ordinary ships. One plant was devoted to making huge interstellar
liners. These giants, made on Venus, were nearly a quarter of a mile
long, and though diminutive in comparison with the giant Nigran ships,
they were still decidedly large. Twelve of these could be completed
within the next month, it was found; and one was immediately set aside
as an officers' headquarters ship. It was recognized that the officers
must be within a few hundred thousand miles of the actual engagements,
for decisions would have to be made without too much loss of time in the
transmission of reports.

The ship must not be brought too near the front lest the officers be
endangered and the entire engagement lost for want of the organizing
central headquarters. The final solution had been the huge central
control ship.

The other large vessels were to be used to ca