<s>
The	O
Stabilised	B-Device
Automatic	I-Device
Bomb	I-Device
Sight	I-Device
(	O
SABS	O
)	O
was	O
a	O
Royal	O
Air	O
Force	O
bombsight	B-Application
used	O
in	O
small	O
numbers	O
during	O
World	O
War	O
II	O
.	O
</s>
<s>
The	O
system	O
worked	O
along	O
similar	O
tachometric	O
principles	O
as	O
the	O
more	O
famous	O
Norden	B-Device
bombsight	I-Device
,	O
but	O
was	O
somewhat	O
simpler	O
,	O
lacking	O
the	O
Norden	O
's	O
autopilot	O
feature	O
.	O
</s>
<s>
Development	O
had	O
begun	O
before	O
the	O
war	O
as	O
the	O
Automatic	O
Bomb	B-Application
Sight	I-Application
,	O
but	O
early	O
bomber	O
operations	O
proved	O
that	O
systems	O
without	O
stabilisation	O
of	O
the	O
bombsight	B-Application
crosshairs	O
were	O
extremely	O
difficult	O
to	O
use	O
under	O
operational	O
conditions	O
.	O
</s>
<s>
A	O
stabiliser	O
for	O
the	O
ABS	O
began	O
development	O
,	O
but	O
to	O
fill	O
the	O
immediate	O
need	O
for	O
a	O
new	O
bombsight	B-Application
,	O
the	O
simpler	O
Mark	B-Device
XIV	I-Device
bomb	I-Device
sight	I-Device
was	O
introduced	O
.	O
</s>
<s>
Some	O
early	O
bombsights	B-Application
had	O
adjustments	O
that	O
could	O
account	O
for	O
wind	O
directly	O
on	O
the	O
nose	O
or	O
tail	O
,	O
but	O
this	O
seriously	O
hampered	O
operational	O
use	O
.	O
</s>
<s>
Using	O
vector	O
algebra	O
to	O
solve	O
for	O
the	O
effect	O
of	O
wind	O
is	O
a	O
common	O
problem	O
in	O
air	O
navigation	O
,	O
and	O
its	O
calculation	O
was	O
semi-automated	O
in	O
the	O
Course	B-Device
Setting	I-Device
Bomb	I-Device
Sight	I-Device
of	O
late	O
World	O
War	O
I	O
vintage	O
.	O
</s>
<s>
To	O
use	O
such	O
a	O
vector	O
bombsight	B-Application
,	O
the	O
bomb	O
aimer	O
first	O
requires	O
an	O
accurate	O
measurement	O
of	O
the	O
speed	O
and	O
direction	O
of	O
the	O
wind	O
.	O
</s>
<s>
This	O
was	O
taken	O
through	O
a	O
variety	O
of	O
methods	O
,	O
often	O
using	O
the	O
bombsight	B-Application
itself	O
as	O
a	O
reference	O
.	O
</s>
<s>
During	O
the	O
1930s	O
,	O
advances	O
in	O
mechanical	B-Device
computers	I-Device
introduced	O
an	O
entirely	O
new	O
way	O
to	O
solve	O
the	O
bombsight	B-Application
problem	O
.	O
</s>
<s>
These	O
sorts	O
of	O
computers	O
were	O
initially	O
introduced	O
for	O
naval	O
uses	O
around	O
the	O
turn	O
of	O
the	O
20th	O
century	O
,	O
later	O
examples	O
including	O
the	O
Admiralty	B-Device
Fire	I-Device
Control	I-Device
Table	I-Device
,	O
Rangekeeper	B-Device
and	O
Torpedo	B-Device
Data	I-Device
Computer	I-Device
.	O
</s>
<s>
This	O
system	O
of	O
progressive	O
estimation	O
is	O
easily	O
adapted	O
to	O
the	O
bombsight	B-Application
role	O
.	O
</s>
<s>
To	O
measure	O
this	O
,	O
the	O
bomb	O
aimer	O
first	O
dials	O
in	O
estimates	O
of	O
the	O
wind	O
speed	O
and	O
direction	O
,	O
which	O
causes	O
the	O
computer	O
to	O
begin	O
moving	O
the	O
bombsights	B-Application
to	O
stay	O
pointed	O
at	O
the	O
target	O
as	O
the	O
bomber	O
moved	O
toward	O
it	O
.	O
</s>
<s>
These	O
tachometric	O
or	O
synchronous	O
bombsights	B-Application
were	O
an	O
area	O
of	O
considerable	O
research	O
during	O
the	O
1930s	O
.	O
</s>
<s>
The	O
US	O
Navy	O
had	O
found	O
that	O
bombsights	B-Application
were	O
almost	O
always	O
used	O
with	O
the	O
sights	O
not	O
properly	O
levelled	O
with	O
respect	O
to	O
the	O
ground	O
,	O
so	O
any	O
angles	O
measured	O
through	O
the	O
sight	O
were	O
wrong	O
.	O
</s>
<s>
Norden	O
's	O
solution	O
used	O
an	O
existing	O
bombsight	B-Application
mechanism	O
known	O
as	O
an	O
"	O
equal	O
distance	O
sight	O
"	O
that	O
was	O
attached	O
to	O
his	O
gyroscopic	O
stabilizer	O
system	O
.	O
</s>
<s>
The	O
Navy	O
asked	O
him	O
to	O
replace	O
the	O
bombsight	B-Application
with	O
a	O
tachometric	O
design	O
on	O
the	O
same	O
stabilizer	O
.	O
</s>
<s>
The	O
Norden	B-Device
bombsight	I-Device
demonstrated	O
itself	O
able	O
to	O
drop	O
bombs	O
within	O
a	O
few	O
yards	O
of	O
its	O
targets	O
from	O
altitudes	O
between	O
.	O
</s>
<s>
News	O
of	O
the	O
Norden	O
filtered	O
to	O
the	O
UK	O
Air	O
Ministry	O
in	O
1938	O
,	O
shortly	O
after	O
they	O
had	O
begun	O
development	O
of	O
their	O
own	O
Automatic	O
Bomb	B-Application
Sight	I-Application
(	O
ABS	O
)	O
.	O
</s>
<s>
In	O
early	O
operations	O
,	O
RAF	O
Bomber	O
Command	O
concluded	O
that	O
their	O
existing	O
bombsights	B-Application
,	O
updated	O
versions	O
of	O
the	O
World	O
War	O
I-era	O
CSBS	B-Device
's	O
,	O
were	O
hopelessly	O
outdated	O
in	O
modern	O
combat	O
.	O
</s>
<s>
When	O
the	O
bomber	O
was	O
turning	O
,	O
the	O
bombsight	B-Application
,	O
fixed	O
to	O
the	O
frame	O
of	O
the	O
aircraft	O
,	O
pointed	O
out	O
to	O
the	O
sides	O
and	O
could	O
not	O
be	O
used	O
to	O
adjust	O
the	O
approach	O
.	O
</s>
<s>
On	O
22	O
December	O
1939	O
,	O
at	O
a	O
pre-arranged	O
meeting	O
on	O
bombsight	B-Application
policy	O
,	O
Air	O
Chief	O
Marshal	O
Sir	O
Edgar	O
Ludlow-Hewitt	O
stated	O
flatly	O
that	O
the	O
CSBS	B-Device
did	O
not	O
meet	O
RAF	O
requirements	O
and	O
asked	O
for	O
a	O
bombsight	B-Application
that	O
would	O
allow	O
the	O
bomber	O
to	O
take	O
any	O
sort	O
of	O
evasive	O
action	O
throughout	O
the	O
bomb	O
run	O
.	O
</s>
<s>
These	O
efforts	O
produced	O
the	O
Mark	B-Device
XIV	I-Device
bomb	I-Device
sight	I-Device
.	O
</s>
<s>
XIV	O
moved	O
the	O
calculator	O
from	O
the	O
bombsight	B-Application
itself	O
to	O
a	O
separate	O
box	O
,	O
which	O
also	O
included	O
instruments	O
that	O
automatically	O
input	O
altitude	O
,	O
airspeed	O
and	O
heading	O
,	O
eliminating	O
the	O
manual	O
setting	O
of	O
these	O
values	O
.	O
</s>
<s>
Although	O
it	O
was	O
a	O
great	O
improvement	O
over	O
the	O
earlier	O
CSBS	B-Device
,	O
it	O
was	O
by	O
no	O
means	O
a	O
precision	O
sighting	O
system	O
,	O
later	O
being	O
referred	O
to	O
as	O
an	O
"	O
area	O
sight	O
"	O
.	O
</s>
<s>
Like	O
the	O
Norden	O
,	O
the	O
stabiliser	O
was	O
separate	O
from	O
the	O
bombsight	B-Application
proper	O
,	O
although	O
in	O
the	O
case	O
of	O
SABS	O
the	O
stabiliser	O
moved	O
the	O
entire	O
ABS	O
bombsight	B-Application
,	O
rather	O
than	O
just	O
the	O
aiming	O
reticle	O
as	O
in	O
the	O
Norden	O
.	O
</s>
<s>
A	O
great	O
debate	O
broke	O
out	O
in	O
the	O
RAF	O
about	O
the	O
relative	O
merits	O
of	O
the	O
two	O
bombsights	B-Application
;	O
although	O
the	O
SABS	O
was	O
more	O
accurate	O
,	O
the	O
Mk	O
.	O
</s>
<s>
The	O
Canberra	O
had	O
initially	O
been	O
designed	O
with	O
no	O
optical	O
bombsight	B-Application
at	O
all	O
,	O
relying	O
entirely	O
on	O
H2S	O
radar	O
.	O
</s>
<s>
However	O
,	O
the	O
required	O
version	O
of	O
the	O
radar	O
was	O
not	O
ready	O
when	O
the	O
aircraft	O
began	O
to	O
arrive	O
,	O
and	O
they	O
were	O
redesigned	O
to	O
carry	O
a	O
bombsight	B-Application
.	O
</s>
<s>
The	O
SABS	O
consisted	O
of	O
three	O
primary	O
parts	O
,	O
the	O
bombsight	B-Application
itself	O
,	O
also	O
known	O
as	O
the	O
"	O
range	O
unit	O
"	O
,	O
the	O
stabilizing	O
system	O
,	O
and	O
the	O
"	O
bombing	O
directional	O
indicator	O
"	O
for	O
the	O
pilot	O
and	O
other	O
indicators	O
.	O
</s>
<s>
The	O
first	O
calculated	O
the	O
angular	O
rate	O
of	O
motion	O
of	O
a	O
stationary	O
location	O
on	O
the	O
ground	O
,	O
which	O
provided	O
the	O
ground	O
speed	O
of	O
the	O
aircraft	O
,	O
and	O
output	O
this	O
to	O
a	O
reflector	O
sight	O
mounted	O
on	O
the	O
left	O
side	O
of	O
the	O
bombsight	B-Application
.	O
</s>
<s>
The	O
key	O
component	O
of	O
this	O
system	O
,	O
and	O
other	O
tachometric	O
designs	O
,	O
was	O
the	O
ball-and-disk	B-Device
integrator	I-Device
.	O
</s>
<s>
To	O
account	O
for	O
the	O
effects	O
of	O
terminal	B-Application
velocity	I-Application
and	O
thus	O
the	O
actual	O
time	O
it	O
took	O
for	O
the	O
bombs	O
to	O
reach	O
the	O
ground	O
,	O
the	O
"	O
bomb	O
class	O
"	O
input	O
moved	O
a	O
pointer	O
over	O
the	O
altitude	O
gauge	O
.	O
</s>
<s>
So	O
,	O
for	O
instance	O
,	O
if	O
a	O
given	O
bomb	O
had	O
a	O
lower	O
terminal	B-Application
velocity	I-Application
than	O
another	O
it	O
would	O
take	O
longer	O
to	O
reach	O
the	O
ground	O
,	O
which	O
is	O
the	O
same	O
as	O
the	O
other	O
bomb	O
being	O
dropped	O
from	O
a	O
slightly	O
higher	O
altitude	O
.	O
</s>
<s>
On	O
the	O
bombsight	B-Application
,	O
this	O
was	O
an	O
electrical	O
contact	O
system	O
attached	O
to	O
the	O
same	O
output	O
shaft	O
as	O
the	O
sight	O
,	O
and	O
a	O
second	O
contact	O
connected	O
to	O
the	O
cam-based	O
trajectory	O
calculator	O
.	O
</s>
<s>
The	O
two	O
contacts	O
,	O
along	O
with	O
automatic	O
indicator	O
slides	O
,	O
one	O
for	O
the	O
viewing	O
angle	O
of	O
the	O
bombsight	B-Application
to	O
the	O
target	O
,	O
the	O
other	O
to	O
the	O
calculated	O
drop	O
angle	O
at	O
the	O
bomb	O
release	O
point	O
,	O
would	O
approach	O
each	O
other	O
as	O
the	O
bomber	O
flew	O
towards	O
the	O
target	O
,	O
and	O
completed	O
the	O
release	O
circuit	O
at	O
the	O
right	O
moment	O
for	O
the	O
drop	O
.	O
</s>
<s>
The	O
same	O
system	O
also	O
included	O
a	O
set	O
of	O
contacts	O
that	O
connected	O
earlier	O
,	O
turning	O
on	O
a	O
red	O
lamp	O
on	O
top	O
of	O
the	O
bombsight	B-Application
and	O
another	O
in	O
front	O
of	O
the	O
pilot	O
.	O
</s>
<s>
The	O
stabiliser	O
unit	O
consisted	O
of	O
two	O
parts	O
,	O
a	O
box	O
containing	O
two	O
gyroscopes	B-Application
,	O
and	O
a	O
pneumatically	O
powered	O
frame	O
that	O
kept	O
the	O
range	O
unit	O
flat	O
in	O
comparison	O
to	O
the	O
ground	O
.	O
</s>
<s>
Gyroscopes	B-Application
have	O
no	O
preferred	O
direction	O
of	O
rotation	O
and	O
will	O
hold	O
whatever	O
angle	O
they	O
initially	O
started	O
up	O
in	O
.	O
</s>
<s>
These	O
set	O
the	O
trail	O
scale	O
and	O
bomb	O
class	O
letter	O
,	O
estimating	O
the	O
amount	O
the	O
bomb	O
would	O
slow	O
in	O
forward	O
motion	O
(	O
trail	O
)	O
and	O
how	O
quickly	O
it	O
would	O
reach	O
the	O
ground	O
due	O
to	O
the	O
effects	O
of	O
terminal	B-Application
velocity	I-Application
(	O
class	O
)	O
.	O
</s>
<s>
At	O
least	O
fifteen	O
minutes	O
before	O
the	O
bomber	O
reached	O
the	O
target	O
,	O
the	O
pilot	O
would	O
open	O
valves	O
to	O
supply	O
air	O
to	O
the	O
bombsight	B-Application
.	O
</s>
<s>
At	O
this	O
point	O
the	O
stabilizer	O
platform	O
was	O
turned	O
on	O
and	O
the	O
bombsight	B-Application
was	O
ready	O
for	O
use	O
.	O
</s>
<s>
At	O
this	O
point	O
the	O
bombsight	B-Application
now	O
has	O
an	O
accurate	O
measurement	O
of	O
the	O
true	O
motion	O
of	O
the	O
aircraft	O
.	O
</s>
<s>
But	O
this	O
makes	O
no	O
difference	O
in	O
terms	O
of	O
the	O
drop	O
;	O
as	O
long	O
as	O
the	O
sight	O
's	O
crosshairs	O
remain	O
on	O
target	O
,	O
the	O
motion	O
over	O
the	O
ground	O
is	O
correctly	O
measured	O
and	O
the	O
bombsight	B-Application
will	O
operate	O
correctly	O
.	O
</s>
