n tops and slopes, for the
Hans, after the destruction of Nu-Yok, had learned quickly that
concealment of their positions was a better protection than a
surrounding wall of disintegrator rays shooting up into the sky.

The Hans, however, had failed to reply with disintegrator rays. For
already this arm, which formerly they had believed invincible, was being
restricted to a limited number of their military units, and their
factories were busy turning out explosive rockets not dissimilar to
those of the Americans in their motive power and atomic detonation.
They had replied with these, shooting them from unrevealed positions,
and at the estimated positions of the Americans.

Since the Americans, not knowing the exact location of the Han outer
line, had shot their barrage over it, and the Hans had fired at unknown
American positions, this first exchange of fire had done little more
than to churn up vast areas of mountain and valley.

The Hans appeared to be elated, to feel that they had driven off an
American attack. I knew better. The next American move, I felt, would be
the occupation of the air, from which they had driven the Hans, and from
swoopers to direct the rocket fire at the city itself. Then, when they
had destroyed this, they would sweep in and hunt down the Hans, man to
man, in the surrounding mountains. Command of the air was still
important in military strategy, but command of the air rested no longer
in the air, but on the ground.

The Hans themselves attempted to scout the American positions from the
air, under cover of a massed attack of ships in "cloud bank" or beaming
formation, but with very little success. Most of their ships were shot
down, and the remainder slid back to the city on sharply inclined
repeller rays, one of them which had its generators badly damaged while
still fifty miles out, collapsed over the city, before it could reach
its berth at the airport, and crashed down through the glass roof of the
city, doing great damage.

Then followed the "air balls," an unforeseen and ingenious resurrection
by the Americans of an old principle of air and submarine tactics,
through a modern application of the principle of remote control.

The air balls took heavy toll of the morale of the Hans before they were
clearly understood by them, and even afterward for that matter.

* * * * *

Their first appearance was quite mysterious. One uneasy night, while the
pulsa