So Power Can Be Brought into Play: SIGINT and the Pusan Perimeter

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

PEOP[E'S

REPUBTIC

OF

CHINA

,,,."":r

$ftho."n

An-tung

a

Sea

of Japan

(East

$eal

rKunu{i

'Korea

Bay

">'\

s.

oDt,I

osu*rn

a

Osan

a

Ch'onan

Line of Farfiest

fnerry

Advame

SepteE&er

195O

Yellow Sea

fwec

SeaJ

Taejon

.

SOUTH

KOREA

4t

6q

l{djedo

(i

t/

t9

U

o*

tniEcloe

,/-i

&6

Pusan

Perimeter

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