<s>
The	O
Torpedo	B-Device
Data	I-Device
Computer	I-Device
(	O
TDC	O
)	O
was	O
an	O
early	O
electromechanical	O
analog	O
computer	O
used	O
for	O
torpedo	O
fire-control	B-Application
on	O
American	O
submarines	O
during	O
World	O
War	O
II	O
.	O
</s>
<s>
Britain	O
,	O
Germany	O
,	O
and	O
Japan	O
also	O
developed	O
automated	O
torpedo	O
fire	B-Application
control	I-Application
equipment	I-Application
,	O
but	O
none	O
were	O
as	O
advanced	O
as	O
the	O
US	O
Navy	O
's	O
TDC	O
,	O
as	O
it	O
was	O
able	O
to	O
automatically	O
track	O
the	O
target	O
rather	O
than	O
simply	O
offering	O
an	O
instantaneous	O
firing	B-Application
solution	I-Application
.	O
</s>
<s>
This	O
unique	O
capability	O
of	O
the	O
TDC	O
set	O
the	O
standard	O
for	O
submarine	O
torpedo	O
fire	B-Application
control	I-Application
during	O
World	O
War	O
II	O
.	O
</s>
<s>
Replacing	O
the	O
previously	O
standard	O
hand-held	O
slide	O
rule-type	O
devices	O
(	O
known	O
as	O
the	O
"	O
banjo	O
"	O
and	O
"	O
is/was	O
"	O
)	O
,	O
the	O
TDC	O
was	O
designed	O
to	O
provide	O
fire-control	B-Application
solutions	O
for	O
submarine	O
torpedo	O
firing	O
against	O
ships	O
running	O
on	O
the	O
surface	O
(	O
surface	O
warships	O
used	O
a	O
different	O
computer	O
)	O
.	O
</s>
<s>
During	O
World	O
War	O
I	O
,	O
computing	O
a	O
target	O
intercept	O
course	O
for	O
a	O
torpedo	O
was	O
a	O
manual	O
process	O
where	O
the	O
fire	B-Application
control	I-Application
party	O
was	O
aided	O
by	O
various	O
slide	O
rules	O
(	O
the	O
U.S.	O
examples	O
were	O
the	O
Mark	O
VIII	O
Angle	O
Solver	O
(	O
colloquially	O
called	O
the	O
"	O
banjo	O
"	O
,	O
for	O
its	O
shape	O
)	O
,	O
and	O
the	O
"	O
Is/Was	O
"	O
circular	O
sliderule	O
(	O
Nasmith	O
Director	O
)	O
,	O
for	O
predicting	O
where	O
a	O
target	O
will	O
be	O
based	O
on	O
where	O
it	O
is	O
now	O
and	O
was	O
)	O
or	O
mechanical	O
calculator/sights	O
.	O
</s>
<s>
It	O
proved	O
to	O
be	O
the	O
best	O
torpedo	O
fire	B-Application
control	I-Application
system	I-Application
of	O
World	O
War	O
II	O
.	O
</s>
<s>
In	O
1943	O
,	O
the	O
Torpedo	B-Device
Data	I-Device
Computer	I-Device
Mark	O
IV	O
was	O
developed	O
to	O
support	O
the	O
Mark	O
18	O
torpedo	O
.	O
</s>
<s>
A	O
straight-running	O
torpedo	O
has	O
a	O
gyroscope-based	O
control	O
system	O
that	O
ensures	O
that	O
the	O
torpedo	O
will	O
run	O
a	O
straight	O
course	O
.	O
</s>
<s>
The	O
TDC	O
was	O
also	O
able	O
to	O
automatically	O
update	O
all	O
torpedo	O
gyro	O
angle	O
settings	O
simultaneously	O
with	O
a	O
fire	B-Application
control	I-Application
solution	O
,	O
which	O
improved	O
the	O
accuracy	O
over	O
systems	O
that	O
required	O
manual	O
updating	O
of	O
the	O
torpedo	O
's	O
course	O
.	O
</s>
<s>
Also	O
,	O
the	O
target	O
bearing	O
angle	O
is	O
different	O
from	O
the	O
point	O
of	O
view	O
of	O
the	O
periscope	B-Language
versus	O
the	O
point	O
of	O
view	O
of	O
the	O
torpedo	O
,	O
which	O
is	O
referred	O
to	O
as	O
torpedo	O
tube	O
parallax	O
.	O
</s>
<s>
During	O
World	O
War	O
II	O
,	O
target	O
course	O
,	O
range	O
,	O
and	O
bearing	O
estimates	O
often	O
had	O
to	O
be	O
generated	O
using	O
periscope	B-Language
observations	O
,	O
which	O
were	O
highly	O
subjective	O
and	O
error	O
prone	O
.	O
</s>
<s>
The	O
TDC	O
needed	O
to	O
be	O
positioned	O
near	O
other	O
fire	B-Application
control	I-Application
equipment	I-Application
to	O
minimize	O
the	O
amount	O
of	O
electromechanical	O
interconnect	O
.	O
</s>
<s>
On	O
World	O
War	O
II	O
submarines	O
,	O
the	O
TDC	O
and	O
other	O
fire	B-Application
control	I-Application
equipment	I-Application
was	O
mounted	O
in	O
the	O
conning	O
tower	O
,	O
which	O
was	O
a	O
very	O
small	O
space	O
.	O
</s>
<s>
The	O
packaging	O
problem	O
was	O
severe	O
and	O
the	O
performance	O
of	O
some	O
early	O
torpedo	O
fire	B-Application
control	I-Application
equipment	I-Application
was	O
hampered	O
by	O
the	O
need	O
to	O
make	O
it	O
small	O
.	O
</s>
<s>
The	O
TDC	O
's	O
target	O
tracking	O
capability	O
was	O
used	O
by	O
the	O
fire	B-Application
control	I-Application
party	O
to	O
continuously	O
update	O
the	O
fire	B-Application
control	I-Application
solution	O
even	O
while	O
the	O
submarine	O
was	O
maneuvering	O
.	O
</s>
<s>
The	O
equations	O
implemented	O
in	O
the	O
angle	O
solver	O
can	O
be	O
found	O
in	O
the	O
Torpedo	B-Device
Data	I-Device
Computer	I-Device
manual	O
.	O
</s>
<s>
The	O
Submarine	O
Torpedo	O
Fire	B-Application
Control	I-Application
Manual	O
discusses	O
the	O
calculations	O
in	O
a	O
general	O
sense	O
and	O
a	O
greatly	O
abbreviated	O
form	O
of	O
that	O
discussion	O
is	O
presented	O
here	O
.	O
</s>
<s>
The	O
general	O
torpedo	O
fire	B-Application
control	I-Application
problem	O
is	O
illustrated	O
in	O
Figure	O
2	O
.	O
</s>
<s>
Most	O
discussions	O
of	O
gyro	O
angle	O
determination	O
take	O
the	O
simpler	O
approach	O
of	O
using	O
Figure	O
3	O
,	O
which	O
is	O
called	O
the	O
torpedo	O
fire	B-Application
control	I-Application
triangle	O
.	O
</s>
<s>
U.S.	O
submarines	O
during	O
World	O
War	O
II	O
preferred	O
to	O
fire	O
their	O
torpedoes	O
at	O
small	O
gyro	O
angles	O
because	O
the	O
TDC	O
's	O
fire	B-Application
control	I-Application
solutions	O
were	O
most	O
accurate	O
for	O
small	O
angles	O
.	O
</s>
<s>
is	O
the	O
angle	O
of	O
the	O
target	O
ship	O
bow	O
relative	O
to	O
the	O
periscope	B-Language
line	O
of	O
sight	O
.	O
</s>
<s>
is	O
the	O
angle	O
of	O
the	O
torpedo	O
course	O
relative	O
to	O
the	O
periscope	B-Language
line	O
of	O
sight	O
.	O
</s>
<s>
As	O
with	O
the	O
angle	O
solver	O
,	O
the	O
equations	O
implemented	O
in	O
the	O
position	O
keeper	O
can	O
be	O
found	O
in	O
the	O
Torpedo	B-Device
Data	I-Device
Computer	I-Device
manual	O
.	O
</s>
<s>
Similar	O
functions	O
were	O
implemented	O
in	O
the	O
rangekeepers	B-Device
for	O
surface	O
ship-based	O
fire	B-Application
control	I-Application
systems	I-Application
.	O
</s>
<s>
For	O
a	O
general	O
discussion	O
of	O
the	O
principles	O
behind	O
the	O
position	O
keeper	O
,	O
see	O
Rangekeeper	B-Device
.	O
</s>
