<s>
The	O
track	B-Algorithm
while	I-Algorithm
scan	I-Algorithm
(	O
TWS	O
)	O
is	O
a	O
mode	O
of	O
radar	B-Application
operation	O
in	O
which	O
the	O
radar	B-Application
allocates	O
part	O
of	O
its	O
power	O
to	O
tracking	O
the	O
target	O
or	O
targets	O
while	O
part	O
of	O
its	O
power	O
is	O
allocated	O
to	O
scanning	O
,	O
unlike	O
the	O
straight	O
tracking	O
mode	O
,	O
when	O
the	O
radar	B-Application
directs	O
all	O
its	O
power	O
to	O
tracking	O
the	O
acquired	O
targets	O
.	O
</s>
<s>
In	O
the	O
TWS	O
mode	O
the	O
radar	B-Application
has	O
a	O
possibility	O
to	O
acquire	O
additional	O
targets	O
as	O
well	O
as	O
providing	O
an	O
overall	O
view	O
of	O
the	O
airspace	O
and	O
helping	O
maintain	O
better	O
situational	O
awareness	O
.	O
</s>
<s>
Early	O
airborne	O
radar	B-Application
systems	I-Application
generally	O
operated	O
purely	O
as	O
tracking	O
systems	O
,	O
with	O
a	O
dedicated	O
radar	B-Application
operator	O
manually	O
"	O
tuning	O
"	O
the	O
system	O
to	O
locate	O
targets	O
in	O
a	O
relatively	O
narrow	O
field-of-view	O
in	O
front	O
of	O
the	O
aircraft	O
.	O
</s>
<s>
The	O
searching	O
area	O
could	O
be	O
moved	O
using	O
a	O
variety	O
of	O
methods	O
,	O
typically	O
phase-shifting	O
or	O
lobe	O
switching	O
on	O
lower	O
frequency	O
systems	O
that	O
required	O
large	O
antennas	O
,	O
or	O
by	O
moving	O
the	O
radar	B-Application
dish	O
on	O
microwave	O
frequency	O
radars	B-Application
.	O
</s>
<s>
Engagements	O
would	O
start	O
with	O
ground	O
controllers	O
guiding	O
the	O
aircraft	O
into	O
the	O
general	O
area	O
of	O
the	O
target	O
via	O
voice	O
commands	O
to	O
the	O
pilot	O
,	O
and	O
once	O
the	O
aircraft	O
got	O
into	O
range	O
its	O
own	O
radar	B-Application
would	O
pick	O
up	O
the	O
target	O
for	O
the	O
final	O
approach	O
when	O
the	O
radar	B-Application
operator	O
would	O
provide	O
voice	O
commands	O
to	O
the	O
pilot	O
.	O
</s>
<s>
Ground-based	O
radars	B-Application
like	O
the	O
SCR-584	O
automated	O
this	O
process	O
early	O
in	O
their	O
evolution	O
.	O
</s>
<s>
In	O
search	O
mode	O
the	O
SCR-584	O
rotated	O
its	O
antenna	O
through	O
360	O
degrees	O
and	O
any	O
returns	O
were	O
plotted	O
on	O
a	O
plan	B-Algorithm
position	I-Algorithm
indicator	I-Algorithm
(	O
PPI	O
)	O
.	O
</s>
<s>
This	O
gave	O
the	O
operators	O
an	O
indication	O
of	O
any	O
targets	O
within	O
its	O
~	O
25	O
mile	O
detection	O
range	O
and	O
their	O
direction	O
relative	O
to	O
the	O
radar	B-Application
van	O
.	O
</s>
<s>
When	O
one	O
of	O
the	O
returns	O
was	O
considered	O
interesting	O
,	O
the	O
radar	B-Application
was	O
flipped	O
to	O
tracking	O
mode	O
and	O
"	O
locked-on	O
"	O
.	O
</s>
<s>
Advances	O
in	O
electronics	O
meant	O
it	O
was	O
only	O
a	O
matter	O
of	O
time	O
before	O
automated	O
radars	B-Application
like	O
the	O
SCR-584	O
could	O
be	O
reduced	O
in	O
size	O
and	O
weight	O
enough	O
to	O
fit	O
into	O
an	O
aircraft	O
.	O
</s>
<s>
The	O
introduction	O
of	O
semi-active	O
radar	B-Application
homing	O
missiles	O
made	O
the	O
lock-on	O
concept	O
especially	O
important	O
.	O
</s>
<s>
These	O
missiles	O
use	O
the	O
launching	O
aircraft	O
's	O
own	O
radar	B-Application
to	O
"	O
paint	O
"	O
the	O
target	O
with	O
a	O
radar	B-Application
signal	O
,	O
the	O
missile	O
listens	O
for	O
the	O
signal	O
being	O
reflected	O
off	O
the	O
target	O
to	O
home	O
in	O
on	O
.	O
</s>
<s>
This	O
requires	O
the	O
radar	B-Application
to	O
be	O
locked	O
on	O
in	O
order	O
to	O
provide	O
a	O
steady	O
guidance	O
signal	O
.	O
</s>
<s>
The	O
drawback	O
is	O
that	O
once	O
the	O
radar	B-Application
is	O
set	O
to	O
tracking	O
a	O
single	O
target	O
,	O
the	O
operator	O
loses	O
information	O
about	O
any	O
other	O
targets	O
.	O
</s>
<s>
This	O
is	O
the	O
problem	O
that	O
track	B-Algorithm
while	I-Algorithm
scan	I-Algorithm
is	O
meant	O
to	O
address	O
.	O
</s>
<s>
In	O
traditional	O
radar	B-Application
systems	I-Application
,	O
the	O
display	O
is	O
purely	O
electrical	O
;	O
signals	O
from	O
the	O
radar	B-Application
dish	O
are	O
amplified	O
and	O
sent	O
directly	O
to	O
an	O
oscilloscope	O
for	O
display	O
.	O
</s>
<s>
Track	B-Algorithm
while	I-Algorithm
scan	I-Algorithm
radars	B-Application
became	O
possible	O
with	O
the	O
introduction	O
of	O
two	O
new	O
technologies	O
:	O
phased-array	O
radars	B-Application
and	O
computer	O
memory	O
devices	O
.	O
</s>
<s>
Much	O
more	O
important	O
to	O
the	O
development	O
of	O
TWS	O
was	O
the	O
development	O
of	O
digital	O
computers	O
and	O
their	O
associated	O
memories	O
,	O
which	O
allowed	O
the	O
radar	B-Application
data	O
to	O
be	O
remembered	O
from	O
scan	O
to	O
scan	O
.	O
</s>
<s>
TWS	O
radars	B-Application
disconnect	O
the	O
display	O
from	O
the	O
antenna	O
,	O
sending	O
the	O
signals	O
to	O
a	O
computer	O
instead	O
of	O
the	O
display	O
.	O
</s>
<s>
The	O
next	O
time	O
the	O
radar	B-Application
returns	O
to	O
that	O
area	O
,	O
any	O
returns	O
are	O
correlated	O
with	O
the	O
original	O
recording	O
,	O
and	O
the	O
track	O
file	O
is	O
updated	O
or	O
discarded	O
as	O
appropriate	O
.	O
</s>
<s>
A	O
second	O
system	O
continuously	O
reads	O
the	O
data	O
in	O
the	O
track	O
files	O
from	O
memory	O
,	O
and	O
displays	O
this	O
on	O
the	O
radar	B-Application
as	O
a	O
series	O
of	O
annotated	O
icons	O
.	O
</s>
<s>
Unlike	O
the	O
straight	O
tracking	O
mode	O
,	O
TWS	O
radars	B-Application
have	O
to	O
solve	O
an	O
additional	O
problem	O
of	O
recognizing	O
whether	O
each	O
target	O
discrimination/detection	O
defines	O
a	O
new	O
target	O
or	O
belongs	O
to	O
already	O
tracked	O
targets	O
.	O
</s>
<s>
With	O
the	O
location	O
of	O
targets	O
known	O
even	O
when	O
the	O
radar	B-Application
antenna	O
is	O
not	O
pointed	O
at	O
them	O
,	O
TWS	O
radars	B-Application
can	O
return	O
to	O
the	O
same	O
area	O
of	O
sky	O
on	O
their	O
next	O
scan	O
and	O
beam	O
additional	O
energy	O
toward	O
the	O
target	O
.	O
</s>
<s>
So	O
in	O
spite	O
of	O
the	O
radar	B-Application
not	O
constantly	O
painting	O
the	O
target	O
as	O
it	O
would	O
in	O
a	O
traditional	O
lock-on	O
,	O
enough	O
energy	O
is	O
sent	O
in	O
that	O
direction	O
to	O
allow	O
a	O
missile	O
to	O
track	O
.	O
</s>
<s>
Advanced	O
phased	O
array	O
radars	B-Application
make	O
this	O
even	O
easier	O
,	O
allowing	O
a	O
signal	O
to	O
be	O
continually	O
directed	O
at	O
the	O
target	O
.	O
</s>
<s>
However	O
,	O
the	O
first	O
operational	O
track-while-scan	B-Algorithm
radar	B-Application
in	O
history	O
was	O
neither	O
passive	B-Algorithm
electronically	I-Algorithm
scanned	I-Algorithm
array	I-Algorithm
nor	O
active	B-Architecture
electronically	I-Architecture
scanned	I-Architecture
array	I-Architecture
radar	B-Application
.	O
</s>
<s>
It	O
was	O
actually	O
the	O
Soviet-made	O
missile	O
guidance	O
,	O
target	O
detection	O
and	O
tracking	O
radar	B-Application
known	O
as	O
B-200	O
,	O
firstly	O
designed	O
in	O
1953	O
by	O
KB-1	O
(	O
today	O
known	O
as	O
NPO	O
Almaz	O
)	O
,	O
as	O
a	O
part	O
of	O
multi-channel	O
,	O
stationary	O
anti-aircraft	O
missile	O
system	O
designated	O
as	O
S-25	O
(	O
Sistema-25	O
,	O
initial	O
name	O
Berkut	O
-	O
Golden	O
eagle	O
,	O
in	O
English	O
)	O
or	O
SA-1	O
Guild	O
(	O
by	O
NATO	O
designation	O
)	O
,	O
which	O
was	O
intended	O
exclusively	O
for	O
defense	O
against	O
possible	O
massive	O
air	O
raid	O
on	O
Moscow	O
and	O
especially	O
Kremlin	O
from	O
long-range	O
strategic	O
USAF	O
bombers	O
(	O
especially	O
the	O
ones	O
like	O
B-47	O
and	O
later	O
B-52	O
,	O
capable	O
of	O
stratospheric	O
flights	O
,	O
which	O
made	O
them	O
completely	O
immune	O
to	O
ordinary	O
anti-aircraft	O
guns	O
)	O
.	O
</s>
<s>
Since	O
the	O
S-25	O
was	O
also	O
designed	O
as	O
the	O
first	O
multi-channel	O
missile	O
system	O
in	O
history	O
(	O
the	O
first	O
one	O
which	O
had	O
the	O
ability	O
to	O
engage	O
multiple	O
targets	O
completely	O
simultaneously	O
-	O
as	O
much	O
as	O
twenty	O
targets	O
by	O
a	O
single	O
battery	O
,	O
each	O
with	O
up	O
to	O
three	O
missiles	O
)	O
,	O
it	O
thus	O
required	O
a	O
proper	O
radar	B-Application
capable	O
of	O
fulfilling	O
such	O
a	O
demanding	O
task	O
,	O
what	O
ultimately	O
resulted	O
in	O
creation	O
of	O
the	O
B-200	O
,	O
as	O
the	O
very	O
first	O
fire-control	O
radar	B-Application
intended	O
for	O
multiple	O
guidance	O
of	O
missiles	O
on	O
multiple	O
different	O
air	O
targets	O
,	O
what	O
was	O
ensured	O
exactly	O
by	O
its	O
TWS	O
ability	O
.	O
</s>
<s>
The	O
USSR	O
created	O
56	O
of	O
those	O
radar	B-Application
sites	O
between	O
1954	O
and	O
1956	O
(	O
as	O
many	O
as	O
there	O
were	O
S-25	O
missile	O
sites	O
)	O
in	O
two	O
large	O
concentric	O
rings	O
around	O
Moscow	O
which	O
represented	O
two	O
lines	O
of	O
anti-aircraft	O
defense	O
,	O
each	O
of	O
them	O
featuring	O
multiple	O
S-25	O
sites	O
(	O
34	O
of	O
those	O
were	O
located	O
on	O
the	O
outer	O
and	O
remaining	O
22	O
on	O
the	O
inner	O
ring	O
)	O
.	O
</s>
<s>
The	O
B-200	O
was	O
a	O
3D	B-Algorithm
,	O
UHF	O
,	O
S/E	B-Algorithm
-band	I-Algorithm
radar	B-Application
,	O
which	O
had	O
instrumented	O
detection	O
range	O
of	O
150km	O
and	O
ability	O
to	O
track	O
as	O
much	O
as	O
30	O
different	O
targets	O
simultaneously	O
(	O
on	O
20	O
of	O
those	O
it	O
could	O
also	O
launch	O
S-25	O
missiles	O
)	O
,	O
while	O
still	O
scanning	O
for	O
new	O
targets	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
radar	B-Application
in	O
the	O
world	O
capable	O
of	O
such	O
features	O
,	O
which	O
will	O
be	O
surpassed	O
for	O
the	O
first	O
time	O
yet	O
half	O
a	O
century	O
later	O
,	O
by	O
modern	O
Russian	O
S-400	O
system	O
(	O
whose	O
92N2	O
fire-control	O
radar	B-Application
can	O
engage	O
as	O
much	O
as	O
80	O
different	O
targets	O
simultaneously	O
,	O
each	O
with	O
two	O
missiles	O
)	O
.	O
</s>
<s>
The	O
B-200	O
also	O
featured	O
very	O
unique	O
and	O
advanced	O
design	O
for	O
its	O
time	O
as	O
well	O
as	O
an	O
unusual	O
operating	O
mode	O
;	O
consisting	O
of	O
two	O
symmetrical	O
antennas	O
(	O
one	O
intended	O
for	O
azimuth	O
and	O
the	O
other	O
one	O
for	O
elevation	O
surveillance	O
)	O
,	O
each	O
featuring	O
two	O
hexagonal	O
,	O
diamond-shaped	O
discs	O
(	O
each	O
as	O
much	O
as	O
10	O
meters	O
high	O
)	O
,	O
both	O
which	O
were	O
rotating	O
around	O
its	O
own	O
axles	O
(	O
like	O
a	O
propeller	O
or	O
windmill	B-Application
)	O
in	O
mutually	O
opposite	O
directions	O
and	O
as	O
fast	O
as	O
50	O
turns	O
per	O
minute	O
,	O
which	O
enabled	O
them	O
as	O
much	O
as	O
target	O
scans	O
.	O
</s>
<s>
Despite	O
not	O
falling	O
in	O
category	O
of	O
modern	O
phased-array	O
radars	B-Application
,	O
the	O
B-200	O
is	O
nevertheless	O
also	O
considered	O
to	O
be	O
the	O
first	O
modern	O
fire-control	O
radar	B-Application
in	O
history	O
(	O
the	O
one	O
intended	O
for	O
missile	O
guidances	O
)	O
,	O
since	O
most	O
of	O
the	O
today	O
's	O
radars	B-Application
of	O
the	O
type	O
share	O
the	O
TWS	O
ability	O
.	O
</s>
<s>
From	O
the	O
Western	O
side	O
,	O
the	O
first	O
operational	O
TWS	O
radar	B-Application
was	O
the	O
Royal	O
Navy	O
's	O
(	O
RN	O
)	O
Type	O
984	O
naval	O
radar	B-Application
,	O
which	O
firstly	O
appeared	O
three	O
years	O
later	O
than	O
Soviet	O
B-200	O
ground-based	O
radar	B-Application
(	O
in	O
1956	O
)	O
,	O
with	O
only	O
three	O
such	O
radars	B-Application
manufactured	O
(	O
for	O
three	O
Royal	O
Navy	O
aircraft	O
carriers	O
-	O
the	O
HMS	O
Eagle	O
,	O
Hermes	O
and	O
Victorious	O
)	O
.	O
</s>
<s>
Also	O
,	O
the	O
Type	O
984	O
was	O
not	O
a	O
fire-control	O
radar	B-Application
and	O
was	O
thus	O
not	O
intended	O
for	O
guidance	O
of	O
missiles	O
,	O
but	O
a	O
radar	B-Application
intended	O
for	O
ground-controlled	O
interception	O
as	O
well	O
as	O
an	O
early	B-Algorithm
warning	I-Algorithm
radar	I-Algorithm
,	O
due	O
to	O
which	O
also	O
required	O
TWS	O
ability	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
Western	O
radar	B-Application
which	O
featured	O
ability	O
to	O
engage	O
aircraft	O
on	O
multiple	O
airborne	O
targets	O
while	O
still	O
simultaneously	O
scanning	O
for	O
new	O
ones	O
.	O
</s>
<s>
The	O
Type	O
984	O
was	O
also	O
the	O
first	O
naval	O
TWS	O
radar	B-Application
in	O
history	O
.	O
</s>
<s>
In	O
the	O
United	O
States	O
,	O
the	O
original	O
tracking	O
radar	B-Application
system	I-Application
was	O
the	O
Semi-Automatic	B-Device
Ground	I-Device
Environment	I-Device
(	O
SAGE	O
)	O
system	O
developed	O
for	O
the	O
US	O
Air	O
Force	O
in	O
1958	O
.	O
</s>
<s>
Early	O
airborne	O
TWS	O
radar	B-Application
typically	O
only	O
tracked	O
a	O
single	O
target	O
while	O
scanning	O
.	O
</s>
<s>
The	O
original	O
TWS	O
airborne	O
set	O
was	O
the	O
Hughes	O
Aircraft	O
AN/ASG	B-Device
-18	I-Device
of	O
the	O
XF-108	O
Rapier	O
,	O
which	O
could	O
track	O
a	O
single	O
target	O
.	O
</s>
<s>
It	O
was	O
not	O
until	O
the	O
introduction	O
of	O
digital	O
computers	O
,	O
and	O
especially	O
microprocessors	B-Architecture
,	O
that	O
TWS	O
in	O
airborne	O
applications	O
became	O
practical	O
.	O
</s>
<s>
Development	O
of	O
TWS	O
generally	O
followed	O
the	O
development	O
of	O
the	O
microprocessors	B-Architecture
that	O
eventually	O
powered	O
them	O
;	O
the	O
AN/AWG	O
-9	O
of	O
the	O
F-14	B-Device
Tomcat	I-Device
used	O
an	O
Intel	B-General_Concept
8080	I-General_Concept
and	O
could	O
track	O
24	O
targets	O
.	O
</s>
