"

Colonel Culver spoke musingly. "Guerilla warfare, the hardest kind to
meet."

* * * * *

Smithy nodded absently. He rose and stared from one of the side
windows that was just level with his eyes. He could see nothing but
the broad expanse of wing, a sheet of smooth gray metal. Along its
leading edge was a row of shimmering disks where great propellers
whirled. From the top of the wing a two-inch Rickert recoilless thrust
forth its snout; it rose in air till the whole weapon was visible,
then settled again and buried itself inside the wing.

They were testing a gun. Smithy knew that inside that wing section
were other guns, and men, and smoothly running motors. The whole ship
was only a giant flying wing of which their own central section was
merely a thickening.

He looked down through a bull's-eye in the floor. The city they had
just left was beneath them. Washington, the nation's capital; the
golden dome of the Capitol Building was slipping swiftly astern. Only
then did he make a belated reply to Culver's statement.

"Well," he said shortly, "they'll have to meet it their own way. We
told them all we knew. And a lot of good that did--not!"

"Five days!" said Culver. "It seems more like five years since the
devils first came out. Nobody knows where they will hit next. But
they're working north--and there's no trouble in telling where they've
been."

Smithy's voice was hot in reply, hot with the intense anger of a
young, aggressive man when confronted by the ponderous motion of a big
organization getting slowly under way.

"If only we'd gone down underground," he exclaimed; "carried the fight
to them! They live there--there must be a whole world underground. We
could have carried in power lines, lighting the place as we went
along. We could have fought 'em with gas. We'd have paid for it, sure
we would, but we'd have given them enough hell to think of down below
so they wouldn't raise so much of it up above.

"But no! We had to fight according to the textbooks. And those red
devils don't fight that way; they never learned the rules."

* * * * *

"Guerilla warfare," Colonel Culver repeated. "There are certain
difficulties about fighting enemies you can't see."

"They're clever," Smithy admitted. "We taught them their lesson down
there in the desert--they've never been seen in daylight since. Out at
night--and their invisible heat-rays setti