and the first
decrypts were delivered
on
14
July.
Typewriters
that
could type Korean characters were
cobbled together. As
of
ro
July,
the traffic
analysts
had
further refined
their
picture
of
the two
North Korean
traffic networks.
One
was
determined to
be a
police
force network
of twelve fairly fixed
outstations. The
other was a
military network
of thirty
outstations with sub-nets
that was later
determined to
be the
principal
command net
of the North Korean
Army. Intercepted
plaintext
translation was well
under
way
by
mid-July
and was hampered
only by the lack
of
linguists.
Even with
this shortage,
the
intercepted
plaintext
was
already
proving
extremely helpful
to the American
effort.
During
the first
two
weeks
of July, nine working
aids and two Korean language
studies
were
completed. Efforts were
so successful that
the
16-3r
July r95o
issue
of the AFSA
Semi-Monthly Report
for
the Office of
Operations
was able to report
that
The Korean traffic is
nort being
processecl
and translations
produced
on
a
z4-hour
basis. This has meant
the streni;thening of clerical and
cryptolog,ic aide staff in
considerable numbers. Tho language
staff
has
also been bolsteled
by
ioans
flom othc'r branches. Coulses in
the
language
are'being offered u'ith
a
vier.v
tor,r.arcl
increasing
efficiency'
in...translating.
By tS August,
the Semi-Monthly Report
claimed to have
brought enough
people
together to
permit
full-time operations
on
the Korean Communist
problem.
By the end of August
there were
fifteen
full-time and five
part-time
personnel
engaged in
this effort.
SIGINT
AND T}{E
PUSAN PERIMETER
The KPA
continued to force U.S.
troops and their allies
southward
until the end of July. Because
of
his
green
troops and
equipment
shortages, General Walker
decided to establish a
defensive line, retreat
behind
it,
and
hold it
at all cost. The Pusan
Perimeter,
as the line came to
be called, was an area in the
southeast corner of South Korea
bounded by the
Naktong
River on
the west, the Sea of Japan
on the east, rugged mountains on the
north,
and the Korea Strait
on the south.
The
perimeter
enclosed
the
port
city of
Pusan,
where U.S. troops and supplies were
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Taegu
arriving,
as well
as
the
city
of Taegu,
where
General
warker
set
up
his
8th Army
Headquarters.
This
defensive perimeter
was
established
on
3r
July
r95o
when
the
last
u.s.
sordiers
crossed
the
Naktong
River.
It
was
held
by
the
u.s.
troops
for
approximately
forty-five
days
until
the
Inchon
campaign
provideilenough
of
a
distraction
that
walker's
forces
could
push
across
the
Niktong
River
and
drive
the
North
Koreans
north.
walker
stationed
his
forces
in
small
manned
points
along
the
perimeter
to
provide
an
early
warning
and
some initial
defense
in
the
case
of
attack,
fading
back
in
the
case
of
a major
assault.
Although
the
number
of
troops
available
to
him
was
growing,
walker
could
not
afford
to
do more
at this
point.
During
the firit
two-thirds
of
August,
walker
faced
uncoordinated
attacks
on four
fronts:
at the
Naktong
Bulge,
around
Taegu
from
two
directions
(north
and
east),
and in
a northeastern
sector
around
yongdok,
Changsa-dong
and Pohang-dong.
The
battle
became
a
,.daily
succession
of crises"
in
which
Walker
had
to
rush his
men
to
Transport
unloads
supplies
for
rJ.S.
troops in
Kore4
at
pusan
U,5.
Army
DUKWs
bring supplies
and
equipment to
shore
from
ships
at
Pusan
Harbor, l(area.
various
points
along the
perimeter
to stop
the North
Koreans.
SIGINT was
vital
to
his efforts at this time because
it
provided
him
with an indication of the
enemy's
movements and
plans
and
allowed him to spread
his men as effectively as
possible
to
repel
the
KPA.
During this desperate
time, the SIGINT
reports contained
interesting and significant
information that
was very
useful
in
efforts
to keep the U.S. operations
successful.
For example, a
few of
the
messages detailed
locations of several
North Korean
infantry
battalions.
Additional intercept
provided
a listing
of the
ammunition being
delivered to the
rst Division after
what they had
previously
held was destroyed by the
Americans. Several
messages
discussed
a serious
radio
outage,
which
prevented
an unidentified
unit from talking to
anyone except the
North Korean 6th
Division.
One
message revealed North
Korean intelligence on the
Americans
and
South Koreans. North
Korean air force messages
described the

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