<s>
High	B-Device
Angle	I-Device
Control	I-Device
System	I-Device
(	O
HACS	B-Device
)	O
was	O
a	O
British	O
anti-aircraft	B-Application
fire-control	B-Application
system	I-Application
employed	O
by	O
the	O
Royal	O
Navy	O
from	O
1931	O
and	O
used	O
widely	O
during	O
World	O
War	O
II	O
.	O
</s>
<s>
HACS	B-Device
calculated	O
the	O
necessary	O
deflection	O
required	O
to	O
place	O
an	O
explosive	O
shell	O
in	O
the	O
location	O
of	O
a	O
target	O
flying	O
at	O
a	O
known	O
height	O
,	O
bearing	O
and	O
speed	O
.	O
</s>
<s>
The	O
HACS	B-Device
was	O
first	O
proposed	O
in	O
the	O
1920s	O
and	O
began	O
to	O
appear	O
on	O
Royal	O
Navy	O
(	O
RN	O
)	O
ships	O
in	O
January	O
1930	O
,	O
when	O
HACS	B-Device
I	O
went	O
to	O
sea	O
in	O
.	O
</s>
<s>
HACS	B-Device
I	O
did	O
not	O
have	O
any	O
stabilization	O
or	O
power	O
assist	O
for	O
director	O
training	O
.	O
</s>
<s>
HACS	B-Device
III	O
which	O
appeared	O
in	O
1935	O
,	O
had	O
provision	O
for	O
stabilization	O
,	O
was	O
hydraulically	O
driven	O
,	O
featured	O
much	O
improved	O
data	O
transmission	O
and	O
it	O
introduced	O
the	O
HACS	B-Device
III	O
Table	O
.	O
</s>
<s>
The	O
HACS	B-Device
III	O
table	O
(	O
computer	O
)	O
had	O
numerous	O
improvements	O
including	O
raising	O
maximum	O
target	O
speed	O
to	O
350	O
knots	O
,	O
continuous	O
automatic	O
fuze	O
prediction	O
,	O
improved	O
geometry	O
in	O
the	O
deflection	O
Screen	O
,	O
and	O
provisions	O
for	O
gyro	O
inputs	O
to	O
provide	O
stabilization	O
of	O
data	O
received	O
from	O
the	O
director	O
.	O
</s>
<s>
The	O
HACS	B-Device
was	O
a	O
control	O
system	O
and	O
was	O
made	O
possible	O
by	O
an	O
effective	O
data	O
transmission	O
network	O
between	O
an	O
external	O
gun	O
director	O
,	O
a	O
below	O
decks	O
fire	B-Application
control	I-Application
computer	I-Application
,	O
and	O
the	O
ship	O
's	O
medium	O
calibre	O
anti-aircraft	B-Application
(	O
AA	O
)	O
guns	O
.	O
</s>
<s>
The	O
early	O
versions	O
of	O
HACS	B-Device
,	O
Mk	O
.	O
</s>
<s>
All	O
of	O
these	O
values	O
were	O
sent	O
via	O
selsyn	B-Algorithm
to	O
the	O
HACS	B-Device
in	O
the	O
High	O
Angle	O
Calculating	O
Position	O
(	O
HACP	O
)	O
located	O
below	O
decks	O
.	O
</s>
<s>
The	O
HACS	B-Device
used	O
these	O
values	O
to	O
calculate	O
the	O
range	O
rate	O
(	O
often	O
called	O
rate	O
along	O
in	O
RN	O
parlance	O
)	O
,	O
which	O
is	O
the	O
apparent	O
target	O
motion	O
along	O
the	O
line	O
of	O
sight	O
.	O
</s>
<s>
The	O
HACS	B-Device
also	O
displayed	O
the	O
predicted	O
bearing	O
and	O
elevation	O
of	O
the	O
target	O
on	O
indicators	O
in	O
the	O
Director	O
tower	O
,	O
or	O
on	O
later	O
variants	O
,	O
the	O
HACS	B-Device
could	O
move	O
the	O
entire	O
Director	O
through	O
Remote	O
Power	O
Control	O
so	O
that	O
it	O
could	O
continue	O
to	O
track	O
the	O
target	O
if	O
the	O
target	O
became	O
obscured	O
.	O
</s>
<s>
The	O
angle	O
measured	O
by	O
the	O
graticule	O
also	O
caused	O
a	O
metal	O
wire	O
to	O
rotate	O
around	O
the	O
face	O
of	O
a	O
large	O
circular	O
display	O
on	O
one	O
side	O
of	O
the	O
HACS	B-Device
,	O
known	O
as	O
the	O
Deflection	O
Display	O
.	O
</s>
<s>
Most	O
guns	O
controlled	O
by	O
the	O
HACS	B-Device
had	O
Fuze	O
Setting	O
Pedestals	O
or	O
Fuze	O
Setting	O
Trays	O
where	O
the	O
correct	O
fuze	O
timing	O
was	O
set	O
on	O
a	O
clockwork	O
mechanism	O
within	O
the	O
AA	O
shell	O
warhead	O
,	O
so	O
that	O
the	O
shell	O
would	O
explode	O
in	O
the	O
vicinity	O
of	O
the	O
target	O
aircraft	O
.	O
</s>
<s>
The	O
HACS	B-Device
was	O
the	O
first	O
Naval	O
AA	O
system	O
to	O
be	O
used	O
against	O
radio	O
controlled	O
aircraft	O
,	O
and	O
achieved	O
the	O
first	O
AA	O
kill	O
against	O
these	O
targets	O
in	O
1933	O
.	O
</s>
<s>
In	O
1935	O
the	O
RN	O
also	O
began	O
to	O
practice	O
HACS	B-Device
controlled	O
shoots	O
of	O
target	O
aircraft	O
at	O
night	O
.	O
</s>
<s>
The	O
RN	O
moved	O
quickly	O
to	O
add	O
true	O
tachometric	O
target	O
motion	O
prediction	O
and	O
radar	O
ranging	O
to	O
the	O
HACS	B-Device
by	O
mid	O
1941	O
.	O
</s>
<s>
However	O
the	O
system	O
,	O
in	O
common	O
with	O
all	O
World	O
War	O
II-era	O
mechanical	O
AA	O
fire	B-Application
control	I-Application
system	I-Application
still	O
had	O
severe	O
limitations	O
as	O
even	O
the	O
highly	O
advanced	O
United	O
States	O
Navy	O
(	O
USN	O
)	O
Mk	B-Application
37	I-Application
system	I-Application
in	O
1944	O
needed	O
an	O
average	O
of	O
1,000	O
rounds	O
of	O
ammunition	O
fired	O
per	O
kill	O
.	O
</s>
<s>
In	O
1940	O
the	O
Gyro	B-Device
Rate	I-Device
Unit	I-Device
(	O
GRU	O
)	O
was	O
added	O
to	O
the	O
HACS	B-Device
system	O
,	O
an	O
analogue	O
computer	O
capable	O
of	O
directly	O
calculating	O
target	O
speed	O
and	O
direction	O
,	O
converting	O
the	O
HACS	B-Device
into	O
a	O
tachymetric	B-Device
system	O
.	O
</s>
<s>
Also	O
in	O
1940	O
,	O
radar	O
ranging	O
was	O
added	O
to	O
the	O
HACS	B-Device
.	O
</s>
<s>
The	O
GRU	O
and	O
its	O
associated	O
computer	O
,	O
the	O
"	O
Gyro	B-Device
Rate	I-Device
Unit	I-Device
Box	O
"	O
(	O
GRUB	O
)	O
no	O
longer	O
assumed	O
straight	O
and	O
level	O
flying	O
on	O
the	O
part	O
of	O
the	O
target	O
.	O
</s>
<s>
RN	O
destroyers	B-Application
were	O
hampered	O
by	O
the	O
lack	O
of	O
good	O
dual-purpose	O
weapons	O
suitable	O
for	O
ships	O
of	O
destroyer	B-Application
size	O
;	O
for	O
much	O
of	O
the	O
war	O
40°	O
was	O
the	O
maximum	O
elevation	O
of	O
the	O
guns	O
equipping	O
such	O
ships	O
,	O
which	O
were	O
consequently	O
unable	O
to	O
engage	O
directly	O
attacking	O
dive	B-Application
bombers	I-Application
,	O
although	O
they	O
could	O
provide	O
"	O
barrage	O
"	O
and	O
"	O
predicted	O
fire	O
"	O
to	O
protect	O
other	O
ships	O
from	O
such	O
attacks	O
.	O
</s>
<s>
Destroyers	B-Application
did	O
not	O
use	O
HACS	B-Device
,	O
but	O
rather	O
the	O
Fuze	B-Device
Keeping	I-Device
Clock	I-Device
(	O
FKC	O
)	O
,	O
a	O
simplified	O
version	O
of	O
HACS	B-Device
.	O
</s>
<s>
Starting	O
in	O
1938	O
all	O
new	O
RN	O
destroyers	B-Application
,	O
from	O
the	O
onwards	O
,	O
were	O
fitted	O
with	O
a	O
FKC	O
and	O
continuous	O
prediction	O
fuse	O
setting	O
trays	O
for	O
each	O
main	O
armament	O
gun	O
.	O
</s>
<s>
WWII	O
experience	O
from	O
all	O
navies	O
showed	O
that	O
dive	B-Application
bombers	I-Application
could	O
not	O
be	O
engaged	O
successfully	O
by	O
any	O
remote	O
computer-predictive	O
AA	O
system	O
using	O
mechanical	O
fuzes	O
due	O
to	O
the	O
lag	O
time	O
in	O
the	O
computer	O
and	O
the	O
minimum	O
range	O
of	O
optical	O
rangefinders	O
.	O
</s>
<s>
In	O
common	O
with	O
other	O
contemporary	O
navies	O
,	O
pre-war	O
designed	O
RN	O
destroyers	B-Application
suffered	O
from	O
a	O
lack	O
of	O
short-range	O
,	O
rapid-fire	O
AA	O
with	O
which	O
to	O
engage	O
dive	B-Application
bombers	I-Application
.	O
</s>
<s>
It	O
was	O
developed	O
to	O
provide	O
computer	O
prediction	O
and	O
radar	O
anti-aircraft	B-Application
fire	O
control	O
to	O
main	O
and	O
secondary	O
armament	O
guns	O
that	O
did	O
not	O
have	O
inherent	O
anti-aircraft	B-Application
capability	O
.	O
</s>
<s>
The	O
ABU	O
was	O
also	O
used	O
with	O
guns	O
that	O
were	O
nominally	O
controlled	O
by	O
the	O
HACS	B-Device
to	O
provide	O
a	O
limited	O
blind	O
fire	O
capability	O
.	O
</s>
<s>
By	O
May	O
1941	O
,	O
RN	O
cruisers	O
,	O
such	O
as	O
,	O
were	O
engaging	O
the	O
Luftwaffe	O
with	O
stabilized	O
HACS	B-Device
IV	O
systems	O
with	O
GRU/GRUB	O
and	O
Type	O
279	O
radar	O
with	O
the	O
Precision	O
Ranging	O
Panel	O
,	O
which	O
gave	O
+	O
/	O
-	O
25	O
yd	O
accuracy	O
out	O
to	O
14,000	O
yds	O
.	O
</s>
<s>
HMS	O
Fiji	O
was	O
sunk	O
in	O
the	O
Battle	O
of	O
Crete	O
after	O
running	O
out	O
of	O
AA	O
ammunition	O
but	O
her	O
HACS	B-Device
IV	O
directed	O
4-inch	O
AA	O
gun	O
battery	O
fended	O
off	O
Luftwaffe	O
attacks	O
for	O
many	O
hours	O
.	O
</s>
<s>
Demonstrating	O
the	O
RN	O
's	O
rapid	O
strides	O
in	O
naval	O
AA	O
gunnery	O
,	O
in	O
May	O
1941	O
,	O
HMS	O
Prince	O
of	O
Wales	O
went	O
to	O
sea	O
with	O
HACS	B-Device
IVGB	O
,	O
with	O
full	O
radar	O
ranging	O
systems	O
,	O
and	O
nine	O
AA	O
associated	O
fire	O
control	O
radars	O
:	O
four	O
Type	O
285	O
radar	O
,	O
one	O
on	O
each	O
High	O
Angle	O
Director	O
Tower	O
(	O
HADT	O
)	O
and	O
four	O
Type	O
282	O
radar	O
,	O
one	O
on	O
each	O
Mk	B-Device
IV	I-Device
director	I-Device
for	O
the	O
QF	O
2	O
pdr	O
(	O
40mm	O
)	O
"	O
pom	O
pom	O
"	O
mounts	O
,	O
and	O
a	O
long	O
range	O
Type	O
281	O
radar	O
Warning	O
Air	O
(	O
WA	O
)	O
radar	O
which	O
also	O
had	O
precision	O
ranging	O
panels	O
for	O
aerial	O
and	O
surface	O
targets	O
.	O
</s>
<s>
This	O
placed	O
HMS	O
Prince	O
of	O
Wales	O
in	O
the	O
forefront	O
of	O
naval	O
HA	O
AA	O
fire	B-Application
control	I-Application
systems	I-Application
at	O
that	O
time	O
.	O
</s>
<s>
Although	O
the	O
shortcomings	O
of	O
HACS	B-Device
are	O
often	O
blamed	O
for	O
the	O
loss	O
of	O
Force	O
Z	O
,	O
the	O
scope	O
of	O
the	O
Japanese	O
attack	O
far	O
exceeded	O
anything	O
the	O
HACS	B-Device
had	O
been	O
designed	O
to	O
handle	O
in	O
terms	O
of	O
aircraft	O
numbers	O
and	O
performance	O
.	O
</s>
<s>
The	O
failure	O
of	O
anti-aircraft	B-Application
gunnery	O
to	O
deter	O
the	O
Japanese	O
bombers	O
was	O
also	O
influenced	O
by	O
unique	O
circumstances	O
.	O
</s>
<s>
The	O
HACS	B-Device
was	O
originally	O
designed	O
with	O
Atlantic	O
conditions	O
in	O
mind	O
and	O
Prince	O
of	O
Waless	O
AA	O
FC	O
radars	O
had	O
become	O
unserviceable	O
in	O
the	O
extreme	O
heat	O
and	O
humidity	O
in	O
Malayan	O
waters	O
and	O
her	O
2-pdr	O
ammunition	O
had	O
deteriorated	O
badly	O
as	O
well	O
.	O
</s>
<s>
The	O
RN	O
made	O
the	O
following	O
claims	O
for	O
ship	O
borne	O
anti-aircraft	B-Application
fire	O
against	O
enemy	O
aircraft	O
,	O
from	O
September	O
1939	O
up	O
to	O
31	O
Dec	O
1942	O
:	O
</s>
<s>
HACS	B-Device
used	O
various	O
director	O
towers	O
that	O
were	O
generally	O
equipped	O
with	O
Type	O
285	O
as	O
it	O
became	O
available	O
.	O
</s>
<s>
This	O
metric	O
wavelength	O
system	O
employed	O
six	O
yagi	O
antennas	O
that	O
could	O
take	O
ranges	O
of	O
targets	O
,	O
and	O
take	O
accurate	O
readings	O
of	O
bearing	O
using	O
a	O
technique	O
known	O
as	O
"	O
lobe	B-Algorithm
switching	I-Algorithm
"	O
but	O
only	O
crude	O
estimates	O
of	O
altitude	O
.	O
</s>
<s>
This	O
situation	O
was	O
not	O
remedied	O
until	O
the	O
introduction	O
of	O
the	O
HACS	B-Device
Mark	O
VI	O
director	O
in	O
1944	O
that	O
was	O
fitted	O
with	O
centimetric	O
Type	O
275	O
radar	O
.	O
</s>
<s>
Another	O
improvement	O
was	O
the	O
addition	O
of	O
Remote	O
Power	O
Control	O
(	O
RPC	O
)	O
,	O
in	O
which	O
the	O
anti-aircraft	B-Application
guns	O
automatically	O
trained	O
with	O
the	O
director	O
tower	O
,	O
with	O
the	O
necessary	O
changes	O
in	O
bearing	O
and	O
elevation	O
to	O
allow	O
for	O
convergent	O
fire	O
.	O
</s>
<s>
HACS	B-Device
Directors	O
fitted	O
to	O
ships	O
in	O
a	O
document	O
dated	O
as	O
"	O
revised	O
Aug	O
1940	O
"	O
:	O
</s>
<s>
HACS	B-Device
III	O
:	O
ABC	O
transmission	O
,	O
AV	O
cradle	O
for	O
15ft	O
HF/RF	O
.	O
</s>
<s>
HACS	B-Device
III*	O
:	O
Similar	O
to	O
MarkIII	O
but	O
with	O
larger	O
windscreen	O
and	O
space	O
for	O
a	O
rate	O
officer	O
.	O
</s>
<s>
HACS	B-Device
III*G	O
as	O
mark	O
III	O
but	O
fitted	O
with	O
GRU	O
and	O
roll	O
stabilization	O
for	O
the	O
layer	O
.	O
</s>
<s>
HACS	B-Device
IV	O
:	O
Similar	O
to	O
MkIII	O
but	O
with	O
circular	O
screen	O
,	O
magslip	B-Algorithm
transmission	O
and	O
roll	O
stabilization	O
for	O
the	O
layer	O
.	O
</s>
<s>
HACS	B-Device
IV	O
G	O
:	O
Mk	O
IV	O
with	O
Gyro	B-Device
rate	I-Device
unit	I-Device
.	O
</s>
<s>
HACS	B-Device
IV	O
GB	O
:	O
Mk	O
IV	O
and	O
fitted	O
with	O
GRU	O
and	O
complete	O
stabilization	O
in	O
laying	O
and	O
training	O
,	O
Keelavite	O
system	O
of	O
power	O
training	O
.	O
</s>
<s>
HACS	B-Device
V	O
:	O
Improved	O
design	O
,	O
partially	O
enclosed	O
,	O
complete	O
stabilization	O
for	O
elevation	O
and	O
training	O
.	O
</s>
<s>
HACS	B-Device
V*	O
:As	O
Mk	O
V	O
but	O
single	O
HF/RF	O
and	O
raised	O
HF/RF	O
compared	O
to	O
Mk	O
V	O
.	O
</s>
