<s>
Rangekeepers	B-Device
were	O
electromechanical	O
fire	B-Application
control	I-Application
computers	I-Application
used	O
primarily	O
during	O
the	O
early	O
part	O
of	O
the	O
20th	O
century	O
.	O
</s>
<s>
They	O
were	O
sophisticated	O
analog	O
computers	O
whose	O
development	O
reached	O
its	O
zenith	O
following	O
World	O
War	O
II	O
,	O
specifically	O
the	O
Computer	O
Mk	O
47	O
in	O
the	O
Mk	O
68	O
Gun	O
Fire	B-Application
Control	I-Application
system	I-Application
.	O
</s>
<s>
During	O
World	O
War	O
II	O
,	O
rangekeepers	B-Device
directed	O
gunfire	O
on	O
land	O
,	O
sea	O
,	O
and	O
in	O
the	O
air	O
.	O
</s>
<s>
While	O
rangekeepers	B-Device
were	O
widely	O
deployed	O
,	O
the	O
most	O
sophisticated	O
rangekeepers	B-Device
were	O
mounted	O
on	O
warships	B-Application
to	O
direct	O
the	O
fire	O
of	O
long-range	O
guns	O
.	O
</s>
<s>
These	O
warship-based	O
computing	O
devices	O
needed	O
to	O
be	O
sophisticated	O
because	O
the	O
problem	O
of	O
calculating	O
gun	O
angles	O
in	O
a	O
naval	O
engagement	O
is	O
very	O
complex	O
.	O
</s>
<s>
The	O
rangekeeper	B-Device
also	O
performed	O
the	O
required	O
ballistics	B-Application
calculations	O
associated	O
with	O
firing	O
a	O
gun	O
.	O
</s>
<s>
This	O
article	O
focuses	O
on	O
US	O
Navy	O
shipboard	O
rangekeepers	B-Device
,	O
but	O
the	O
basic	O
principles	O
of	O
operation	O
are	O
applicable	O
to	O
all	O
rangekeepers	B-Device
regardless	O
of	O
where	O
they	O
were	O
deployed	O
.	O
</s>
<s>
A	O
rangekeeper	B-Device
is	O
defined	O
as	O
an	O
analog	O
fire	B-Application
control	I-Application
system	I-Application
that	O
performed	O
three	O
functions	O
:	O
</s>
<s>
The	O
rangekeeper	B-Device
continuously	O
computed	O
the	O
current	O
target	O
bearing	O
.	O
</s>
<s>
The	O
rangekeeper	B-Device
must	O
predict	O
where	O
the	O
target	O
will	O
be	O
at	O
the	O
time	O
of	O
projectile	O
arrival	O
.	O
</s>
<s>
The	O
projectile	O
point	O
of	O
impact	O
is	O
a	O
function	O
of	O
many	O
variables	O
,	O
including	O
:	O
gun	O
azimuth	O
,	O
gun	O
elevation	O
,	O
wind	O
speed	O
and	O
direction	O
,	O
air	O
resistance	O
,	O
gravity	O
,	O
latitude	O
,	O
gun/sight	O
parallax	B-Device
,	O
barrel	O
wear	O
,	O
powder	O
load	O
,	O
and	O
projectile	O
type	O
.	O
</s>
<s>
The	O
early	O
history	O
of	O
naval	O
fire	B-Application
control	I-Application
was	O
dominated	O
by	O
the	O
engagement	O
of	O
targets	O
within	O
visual	O
range	O
(	O
also	O
referred	O
to	O
as	O
direct	O
fire	O
)	O
.	O
</s>
<s>
Between	O
the	O
American	O
Civil	O
War	O
and	O
1905	O
,	O
numerous	O
small	O
improvements	O
were	O
made	O
in	O
fire	B-Application
control	I-Application
,	O
such	O
as	O
telescopic	O
sights	O
and	O
optical	O
rangefinders	B-Algorithm
.	O
</s>
<s>
Around	O
1905	O
,	O
mechanical	O
fire	B-Application
control	I-Application
aids	O
began	O
to	O
become	O
available	O
,	O
such	O
as	O
the	O
Dreyer	O
Table	O
,	O
Dumaresq	B-Device
(	O
which	O
was	O
also	O
part	O
of	O
the	O
Dreyer	O
Table	O
)	O
,	O
and	O
,	O
but	O
these	O
devices	O
took	O
a	O
number	O
of	O
years	O
to	O
become	O
widely	O
deployed	O
.	O
</s>
<s>
These	O
devices	O
were	O
early	O
forms	O
of	O
rangekeepers	B-Device
.	O
</s>
<s>
While	O
the	O
British	O
were	O
thought	O
by	O
some	O
to	O
have	O
the	O
finest	O
fire	B-Application
control	I-Application
system	I-Application
in	O
the	O
world	O
at	O
that	O
time	O
,	O
during	O
the	O
Battle	O
of	O
Jutland	O
only	O
3%	O
of	O
their	O
shots	O
actually	O
struck	O
their	O
targets	O
.	O
</s>
<s>
At	O
that	O
time	O
,	O
the	O
British	O
primarily	O
used	O
a	O
manual	O
fire	B-Application
control	I-Application
system	I-Application
.	O
</s>
<s>
The	O
one	O
British	O
ship	O
in	O
the	O
battle	O
that	O
had	O
a	O
mechanical	O
fire	B-Application
control	I-Application
system	I-Application
turned	O
in	O
the	O
best	O
shooting	O
results	O
.	O
</s>
<s>
This	O
experience	O
contributed	O
to	O
rangekeepers	B-Device
becoming	O
standard	O
issue	O
.	O
</s>
<s>
The	O
US	O
Navy	O
's	O
first	O
deployment	O
of	O
a	O
rangekeeper	B-Device
was	O
on	O
the	O
in	O
1916	O
.	O
</s>
<s>
Because	O
of	O
the	O
limitations	O
of	O
the	O
technology	O
at	O
that	O
time	O
,	O
the	O
initial	O
rangekeepers	B-Device
were	O
crude	O
.	O
</s>
<s>
During	O
World	O
War	O
I	O
,	O
the	O
rangekeepers	B-Device
could	O
generate	O
the	O
necessary	O
angles	O
automatically	O
,	O
but	O
sailors	O
had	O
to	O
manually	O
follow	O
the	O
directions	O
of	O
the	O
rangekeepers	B-Device
(	O
a	O
task	O
called	O
"	O
pointer	O
following	O
"	O
or	O
"	O
follow	O
the	O
pointer	O
"	O
)	O
.	O
</s>
<s>
During	O
World	O
War	O
II	O
,	O
servomechanisms	O
(	O
called	O
"	O
power	O
drives	O
"	O
in	O
the	O
U.S.	O
Navy	O
and	O
RPC	O
in	O
the	O
Royal	O
Navy	O
)	O
were	O
developed	O
that	O
allowed	O
the	O
guns	O
to	O
automatically	O
steer	O
to	O
the	O
rangekeeper	B-Device
's	O
commands	O
with	O
no	O
manual	O
intervention	O
.	O
</s>
<s>
In	O
the	O
1930s	O
RPC	O
was	O
used	O
for	O
naval	O
searchlight	O
control	O
and	O
during	O
WW2	O
it	O
was	O
progressively	O
installed	O
on	O
pom-pom	O
mounts	O
and	O
directors	B-Device
,	O
4-inch	O
,	O
4.5-inch	O
and	O
5.25-inch	O
gun	O
mounts	O
.	O
</s>
<s>
During	O
their	O
long	O
service	O
life	O
,	O
rangekeepers	B-Device
were	O
updated	O
often	O
as	O
technology	O
advanced	O
,	O
and	O
by	O
World	O
War	O
II	O
they	O
were	O
a	O
critical	O
part	O
of	O
an	O
integrated	O
fire	B-Application
control	I-Application
system	I-Application
.	O
</s>
<s>
The	O
incorporation	O
of	O
radar	B-Application
into	O
the	O
fire	B-Application
control	I-Application
system	I-Application
early	O
in	O
World	O
War	O
II	O
provided	O
ships	O
with	O
the	O
ability	O
to	O
conduct	O
effective	O
gunfire	O
operations	O
at	O
long	O
range	O
in	O
poor	O
weather	O
and	O
at	O
night	O
.	O
</s>
<s>
During	O
World	O
War	O
II	O
,	O
rangekeeper	B-Device
capabilities	O
were	O
expanded	O
to	O
the	O
extent	O
that	O
the	O
name	O
"	O
rangekeeper	B-Device
"	O
was	O
deemed	O
to	O
be	O
inadequate	O
.	O
</s>
<s>
The	O
term	O
"	O
computer	O
,	O
"	O
which	O
had	O
been	O
reserved	O
for	O
human	O
calculators	O
,	O
came	O
to	O
be	O
applied	O
to	O
the	O
rangekeeper	B-Device
equipment	O
.	O
</s>
<s>
After	O
World	O
War	O
II	O
,	O
digital	O
computers	O
began	O
to	O
replace	O
rangekeepers	B-Device
.	O
</s>
<s>
However	O
,	O
components	O
of	O
the	O
analog	O
rangekeeper	B-Device
system	O
continued	O
in	O
service	O
with	O
the	O
US	O
Navy	O
until	O
the	O
1990s	O
.	O
</s>
<s>
The	O
battleship	B-Application
during	O
a	O
1945	O
test	O
was	O
able	O
to	O
maintain	O
an	O
accurate	O
firing	B-Application
solution	I-Application
on	O
a	O
target	O
during	O
a	O
series	O
of	O
high-speed	O
turns	O
.	O
</s>
<s>
It	O
is	O
a	O
major	O
advantage	O
for	O
a	O
warship	B-Application
to	O
be	O
able	O
to	O
maneuver	O
while	O
engaging	O
a	O
target	O
.	O
</s>
<s>
Night	O
naval	O
engagements	O
at	O
long	O
range	O
became	O
feasible	O
when	O
radar	B-Application
data	O
could	O
be	O
input	O
to	O
the	O
rangekeeper	B-Device
.	O
</s>
<s>
The	O
effectiveness	O
of	O
this	O
combination	O
was	O
demonstrated	O
in	O
November	O
1942	O
at	O
the	O
Third	O
Battle	O
of	O
Savo	O
Island	O
when	O
the	O
engaged	O
the	O
Japanese	O
battlecruiser	B-Application
at	O
a	O
range	O
of	O
at	O
night	O
.	O
</s>
<s>
The	O
Japanese	O
during	O
World	O
War	O
II	O
did	O
not	O
develop	O
radar	B-Application
or	O
automated	O
fire	B-Application
control	I-Application
to	O
the	O
level	O
of	O
the	O
US	O
Navy	O
and	O
were	O
at	O
a	O
significant	O
disadvantage	O
.	O
</s>
<s>
The	O
Royal	O
Navy	O
began	O
to	O
introduce	O
gyroscopic	O
stabilization	O
of	O
their	O
director	O
gunsights	O
in	O
World	O
War	O
One	O
and	O
by	O
the	O
start	O
of	O
World	O
War	O
Two	O
all	O
warships	B-Application
fitted	O
with	O
director	O
control	O
had	O
gyroscopically	O
controlled	O
gunsights	O
.	O
</s>
<s>
The	O
last	O
combat	O
action	O
for	O
the	O
analog	O
rangekeepers	B-Device
,	O
at	O
least	O
for	O
the	O
US	O
Navy	O
,	O
was	O
in	O
the	O
1991	O
Persian	B-Application
Gulf	I-Application
War	I-Application
when	O
the	O
rangekeepers	B-Device
on	O
the	O
s	O
directed	O
their	O
last	O
rounds	O
in	O
combat	O
.	O
</s>
<s>
Rangekeepers	B-Device
were	O
very	O
large	O
,	O
and	O
the	O
ship	O
designs	O
needed	O
to	O
make	O
provisions	O
to	O
accommodate	O
them	O
.	O
</s>
<s>
The	O
rangekeepers	B-Device
required	O
a	O
large	O
number	O
of	O
electrical	O
signal	O
cables	O
for	O
synchro	O
data	O
transmission	O
links	O
over	O
which	O
they	O
received	O
information	O
from	O
the	O
various	O
sensors	O
(	O
e.g.	O
</s>
<s>
gun	O
director	O
,	O
pitometer	O
,	O
rangefinder	B-Algorithm
,	O
gyrocompass	O
)	O
and	O
sent	O
commands	O
to	O
the	O
guns	O
.	O
</s>
<s>
As	O
such	O
,	O
the	O
accuracy	O
of	O
battleship	B-Application
guns	O
was	O
≈1%	O
of	O
range	O
(	O
sometimes	O
better	O
,	O
sometimes	O
worse	O
)	O
.	O
</s>
<s>
Internal	B-Application
ballistics	I-Application
:	O
Guns	O
do	O
wear	O
,	O
and	O
this	O
aging	O
must	O
be	O
taken	O
into	O
account	O
by	O
keeping	O
an	O
accurate	O
count	O
of	O
the	O
number	O
of	O
projectiles	O
sent	O
through	O
the	O
barrel	O
(	O
this	O
count	O
is	O
reset	O
to	O
zero	O
after	O
the	O
installation	O
of	O
a	O
new	O
liner	O
)	O
.	O
</s>
<s>
External	O
ballistics	B-Application
:	O
Different	O
projectiles	O
have	O
different	O
ballistic	O
characteristics	O
.	O
</s>
<s>
Parallax	B-Device
correction	O
:	O
In	O
general	O
,	O
the	O
position	O
of	O
the	O
gun	O
and	O
target	O
spotting	O
equipment	O
(	O
radar	B-Application
,	O
mounted	O
on	O
the	O
gun	O
director	O
,	O
pelorus	O
,	O
etc	O
)	O
are	O
in	O
different	O
locations	O
on	O
a	O
ship	O
.	O
</s>
<s>
This	O
creates	O
a	O
parallax	B-Device
error	O
for	O
which	O
corrections	O
must	O
be	O
made	O
.	O
</s>
<s>
Rangefinders	B-Algorithm
:	O
Optical	O
devices	O
for	O
determining	O
the	O
range	O
to	O
a	O
target	O
.	O
</s>
<s>
Meteorological	O
sensors	O
:	O
Temperature	O
,	O
wind	O
speed	O
,	O
and	O
humidity	O
all	O
have	O
an	O
effect	O
on	O
the	O
ballistics	B-Application
of	O
a	O
projectile	O
.	O
</s>
<s>
U.S.	O
Navy	O
rangekeepers	B-Device
and	O
analog	O
computers	O
did	O
not	O
consider	O
different	O
wind	O
speeds	O
at	O
differing	O
altitudes	O
.	O
</s>
<s>
To	O
illustrate	O
the	O
complexity	O
,	O
Table	O
1	O
lists	O
the	O
types	O
of	O
input	O
for	O
the	O
Ford	O
Mk	O
1	O
Rangekeeper	B-Device
(	O
ca	O
1931	O
)	O
.	O
</s>
<s>
However	O
,	O
even	O
with	O
all	O
this	O
data	O
,	O
the	O
rangekeeper	B-Device
's	O
position	O
predictions	O
were	O
not	O
infallible	O
.	O
</s>
<s>
The	O
rangekeeper	B-Device
's	O
prediction	O
characteristics	O
could	O
be	O
used	O
against	O
it	O
.	O
</s>
<s>
Because	O
the	O
rangekeepers	B-Device
are	O
constantly	O
predicting	O
new	O
positions	O
for	O
the	O
target	O
,	O
it	O
was	O
unlikely	O
that	O
subsequent	O
salvos	O
would	O
strike	O
the	O
position	O
of	O
the	O
previous	O
salvo	O
.	O
</s>
<s>
Practical	O
rangekeepers	B-Device
had	O
to	O
assume	O
that	O
targets	O
were	O
moving	O
in	O
a	O
straight-line	O
path	O
at	O
a	O
constant	O
speed	O
,	O
to	O
keep	O
complexity	O
within	O
acceptable	O
limits	O
.	O
</s>
<s>
A	O
sonar	O
rangekeeper	B-Device
was	O
built	O
to	O
track	O
a	O
target	O
circling	O
at	O
a	O
constant	O
radius	O
of	O
turn	O
,	O
but	O
that	O
function	O
was	O
disabled	O
.	O
</s>
<s>
The	O
fire	B-Application
control	I-Application
equations	O
implemented	O
during	O
World	O
War	O
II	O
on	O
analog	O
rangekeepers	B-Device
are	O
the	O
same	O
equations	O
implemented	O
later	O
on	O
digital	O
computers	O
.	O
</s>
<s>
The	O
key	O
difference	O
is	O
that	O
the	O
rangekeepers	B-Device
solved	O
the	O
equations	O
mechanically	O
.	O
</s>
<s>
Ball-and-disk	B-Device
integrators	I-Device
performed	O
the	O
integration	O
operation	O
.	O
</s>
<s>
Differentiation	B-Algorithm
was	O
performed	O
by	O
using	O
an	O
integrator	O
in	O
a	O
feedback	O
loop	O
.	O
</s>
<s>
Rangekeepers	B-Device
used	O
a	O
number	O
of	O
cams	O
to	O
generate	O
function	O
values	O
.	O
</s>
<s>
Many	O
face	O
cams	O
(	O
flat	O
discs	O
with	O
wide	O
spiral	O
grooves	O
)	O
were	O
used	O
in	O
both	O
rangekeepers	B-Device
.	O
</s>
<s>
For	O
surface	O
fire	B-Application
control	I-Application
(	O
the	O
Mk	O
.	O
</s>
<s>
8	O
Range	O
Keeper	O
)	O
,	O
a	O
single	O
flat	O
cam	O
was	O
sufficient	O
to	O
define	O
ballistics	B-Application
.	O
</s>
<s>
1/1A	O
computer	O
provided	O
mechanical	O
time	O
fuse	O
setting	O
,	O
time	O
of	O
flight	O
(	O
this	O
time	O
is	O
from	O
firing	O
to	O
bursting	O
at	O
or	O
near	O
the	O
target	O
)	O
,	O
time	O
of	O
flight	O
divided	O
by	O
predicted	O
range	O
,	O
and	O
superelevation	O
combined	O
with	O
vertical	O
parallax	B-Device
correction	O
.	O
</s>
<s>
During	O
WWII	O
,	O
all	O
the	O
major	O
warring	O
powers	O
developed	O
rangekeepers	B-Device
to	O
different	O
levels	O
.	O
</s>
<s>
Rangekeepers	B-Device
were	O
only	O
one	O
member	O
of	O
a	O
class	O
of	O
electromechanical	O
computers	O
used	O
for	O
fire	B-Application
control	I-Application
during	O
World	O
War	O
II	O
.	O
</s>
<s>
US	O
bombers	O
used	O
the	O
Norden	B-Device
bombsight	I-Device
,	O
which	O
used	O
similar	O
technology	O
to	O
the	O
rangekeeper	B-Device
for	O
predicting	O
bomb	O
impact	O
points	O
.	O
</s>
<s>
US	O
submarines	O
used	O
the	O
TDC	B-Device
to	O
compute	O
torpedo	O
launch	O
angles	O
.	O
</s>
<s>
This	O
device	O
also	O
had	O
a	O
rangekeeping	B-Device
function	O
that	O
was	O
referred	O
to	O
as	O
"	O
position	O
keeping.	O
"	O
</s>
<s>
This	O
was	O
the	O
only	O
submarine-based	O
fire	B-Application
control	I-Application
computer	I-Application
during	O
World	O
War	O
II	O
that	O
performed	O
target	O
tracking	O
.	O
</s>
<s>
Because	O
space	O
within	O
a	O
submarine	O
hull	O
is	O
limited	O
,	O
the	O
TDC	B-Device
designers	O
overcame	O
significant	O
packaging	O
challenges	O
in	O
order	O
to	O
mount	O
the	O
TDC	B-Device
within	O
the	O
allocated	O
volume	O
.	O
</s>
