<s>
The	O
player	O
selects	O
from	O
a	O
jet	B-Application
fighter	I-Application
or	O
helicopter	B-Application
,	O
shoot	O
enemies	O
in	O
the	O
air	O
and	O
ground	O
,	O
collect	O
power-ups	O
,	O
and	O
defeat	O
bosses	O
to	O
advance	O
levels	O
.	O
</s>
<s>
The	O
jet	B-Application
fighter	I-Application
always	O
shoots	O
straight	O
forward	O
;	O
power-ups	O
increase	O
the	O
width	O
and	O
strength	O
of	O
its	O
shots	O
.	O
</s>
<s>
The	O
helicopter	B-Application
fires	O
thinner	O
and	O
weaker	O
shots	O
,	O
but	O
turns	O
in	O
the	O
direction	O
it	O
moves	O
(	O
similar	O
to	O
the	O
later	O
Zero	B-Application
Gunner	I-Application
)	O
,	O
giving	O
it	O
great	O
range	O
;	O
powerups	O
increase	O
the	O
strength	O
of	O
shots	O
,	O
as	O
well	O
as	O
the	O
number	O
of	O
bullets	O
per	O
shot	O
(	O
adding	O
a	O
small	O
"	O
spread	O
"	O
effect	O
to	O
the	O
shot	O
while	O
moving	O
around	O
)	O
.	O
</s>
<s>
Both	O
the	O
fighter	O
and	O
the	O
helicopter	B-Application
also	O
start	O
with	O
three	O
bombs	O
which	O
wipe	O
out	O
everything	O
in	O
their	O
path	O
,	O
including	O
enemy	O
shots	O
.	O
</s>
<s>
These	O
bombs	O
are	O
also	O
unique	O
compared	O
to	O
similar	O
games	O
,	O
in	O
that	O
they	O
produce	O
a	O
line	O
of	O
small	O
horizontal	O
blasts	O
that	O
can	O
be	O
"	O
directed	O
"	O
at	O
the	O
line	O
travels	O
across	O
the	O
ground	O
,	O
by	O
pressing	O
left	O
and	O
right	O
(	O
similar	O
to	O
the	O
helicopter	B-Application
's	O
shots	O
)	O
.	O
</s>
<s>
"	O
Air	B-Application
Duel	I-Application
"	O
is	O
a	O
challenging	O
game	O
,	O
and	O
later	O
levels	O
can	O
become	O
nearly	O
unplayable	O
if	O
a	O
single	O
life	O
is	O
lost	O
.	O
</s>
<s>
All	O
of	O
GunForce	B-Application
II	I-Application
's	O
music	O
comes	O
from	O
Air	B-Application
Duel	I-Application
,	O
though	O
not	O
all	O
tracks	O
were	O
used	O
and	O
both	O
games	O
are	O
presumably	O
took	O
place	O
in	O
the	O
same	O
setting	O
.	O
</s>
<s>
The	O
underwater	O
path	O
of	O
the	O
first	O
mission	O
of	O
Metal	B-Application
Slug	I-Application
3	I-Application
features	O
a	O
melody	O
which	O
is	O
a	O
remix	O
of	O
Air	B-Application
Duel	I-Application
's	O
3rd	O
&	O
10th	O
stages	O
 '	O
theme	O
.	O
</s>
<s>
In	O
Japan	O
,	O
Game	O
Machine	O
listed	O
Air	B-Application
Duel	I-Application
on	O
their	O
July	O
15	O
,	O
1990	O
issue	O
as	O
being	O
the	O
fourth	O
most-successful	O
table	O
arcade	O
unit	O
of	O
the	O
month	O
.	O
</s>
