<s>
is	O
a	O
1980	B-Application
arcade	B-Application
video	I-Application
game	I-Application
developed	O
and	O
published	O
by	O
Sega	O
.	O
</s>
<s>
N-Sub	B-Application
was	O
later	O
ported	O
by	O
Sega	O
as	O
a	O
launch	O
game	O
for	O
the	O
SG-1000	B-Operating_System
in	O
1983	O
though	O
as	O
with	O
all	O
SG-1000	B-Operating_System
games	O
,	O
it	O
only	O
saw	O
a	O
release	O
in	O
Japan	O
and	O
PAL	O
regions	O
.	O
</s>
<s>
The	O
object	O
of	O
the	O
game	O
is	O
to	O
maneuver	O
an	O
on-screen	O
submarine	O
,	O
the	O
"	O
N-Sub	B-Application
,	O
"	O
with	O
the	O
joystick	B-Device
and	O
sink	O
the	O
enemy	O
fleet	O
with	O
torpedo	O
fire	O
in	O
the	O
Cobalt	O
Blue	O
Sea	O
.	O
</s>
<s>
Enemy	O
ships	O
attack	O
the	O
N-Sub	B-Application
with	O
missiles	O
,	O
torpedoes	O
and	O
depth	B-Device
charges	I-Device
.	O
</s>
