of the satellite. Far
below the surface lay the city of Zbardk, the largest of the few
remaining strongholds of the human race. At one portal of the city a
torpedo-shaped, stubby-winged rocket plane rested in the carriage of a
catapult. Near it the captain addressed briefly the six men normally
composing his crew.

"Men, you already know that our cruise today is not an ordinary patrol.
We are to go to One, there to destroy a base of the hexans. We have
perhaps one chance in ten thousand of returning. Therefore I am taking
only one man--barely enough to operate the plane. Volunteers step one
pace forward."

The six stepped forward as one man, and a smile came over the worn
face of their leader as he watched them draw lots for the privilege of
accompanying him to probable death. The two men entered the body of the
torpedo, sealed the openings and waited.

"Free exits?" snapped the Captain of the Portal, and twelve keen-eyed
observers studied minutely screens and instrument panels connected to
the powerful automatic lookout stations beneath the rims of the widely
separated volcanic craters from which their craft could issue into
Callisto's somber night.

"No hexan radiation can be detected from Exit Eight," came the report.
The Captain of the Portal raised an arm in warning, threw in the guides,
and the two passengers were hurled violently backward, deep into their
cushioned seats, as the catapult shot their plane down the runway. As
the catapult's force was spent automatic trips upon the undercarriage
actuated the propelling rockets and mile after mile, with rapidly
mounting velocity, the plane sped through the tube. As the exit was
approached, the tunnel described a long vertical curve, so that when the
opening into the shaft of the crater was reached and the undercarriage
was automatically detached, the vessel was projected almost vertically
upward. Such was its velocity and so powerful was the liquid propellant
of its rocket motors, that the eye could not follow the flight of the
warship as it tore through the thin layer of the atmosphere and hurled
itself out into the depths of space.

"Did we get away?" asked the captain, hands upon his controls and eyes
upon his moving chart of space.

"I believe so, sir," answered the other officer, at the screens of the
six periscopic devices which covered the full sphere of vision. "No
reports from the rim, and all screens blank." Once more a vessel had
issued from the j