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eclassified and a roved for release b NSA on 05-27-2014 ursuantto E.O. 1352 
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Lecture Strategic Intelligence School 

Comm.and and Staff College 

Signal Intelligence and COJDJDUnication Security 

1 Introduction 

Gentlemen at this point in your course of instruction 

you are studying sources of information and how this informa 

tion is processed One source with which some of you are 

perhaps familiar is that information derived from tapping 

the enemy s communications channels This source is labeled 

signal intelligence Closely allied with the activities 

associated with the collection of signal intelligence is the 

countermeasure of signal intelligence or as it is dalled 

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communication security The latter embraces all activities 

designed to deny to the enemy that intelligence which he 

might gain from:~ =~::_=c~~~?~s These two subJects 

~·~ ~~ related.v that we c~ot~lk about one without 

including the other 

Before we discuss the technical details of signal in 

telligence and communication security operations let us 

e~e first the history of these activities in our army 

~alllllt a little about the successes which have been attained 

to establish these two functions among the most important 

of our intelligence system 

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,.,. 

This course is labelled Signal Intelligence and Commun! 

cation Security I don t thllnk it necessary to go far back 

into their history but it s necessary to define what we re 

going to talk about 

Signal intelligence is the product obtained from intercep 

tion and analysis of traffic passed by the various means of 

communication and from the detection of secret inks micro 

photographs and open codes Communication securitz embraces 

all measures designed to deny to unauthorized persons such 

information of military value as might be derived from our 

communications 

Some people call signal intelligence and communication 

security Siamese twins because they are so closely attached 

and related to each other that you can hardly speak of one 

without bringing the other into the picture It would be a 

pretty good analogy to say that they are the obverse and re 

verse sides or the heads and tails of the same coin piece 

They employ arts or sciences which have been known and prac 

ticed from the very earliest days of writing but it was not 

until World War I that the Army was greatly concerned with 

them for until then signal intelligence and communicat~on 

security activities were not very extensive or on an important 

scale Largely as a result of the invention of radio and of its 

rapid and extensive introduction into military operations it 

became necessary for the Army to give a great deal more attention 

to signal intelligence and communication security activities 

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To recapitulate briefly the stor1 of Signal Intelli 

gence and Communication security has been one of gradual 

consolidati~n of what were once regarded or at least prac 

ticed as independent arts The phenomenal growth or elec 

trical communications coupled with the relatively easy 

opportunities tor interception which characterize them 

have led to widespread developments 1n the fields of Signal 

Intelligence and Communication Security Today the crypto 

graphic systems of World War I are regarded as primitive as 

bows and arrows and the volume and importance of intelli 

gence derived from communications has increased a hundred 

fold The future holds still greater promise for two reasons 

Pirst the coordination between signal intelligence and 

communication security is being turther improved day by day 

The strides which have been made in both fields are closely 

interrelated The constant and immediate excbange of 1n 

formation between the specialist who studies the enemy s 

communications and the one who devises the means b'y which 

the security of oUl' own communications is maintained on a 

high level is absolutely essential Thereby the analyst 

is warned of possible new security techniques which may 1n 

tact already be 1n use by the enemy The findings of the 

analyst in turn contripute to improvements 1n security by 

exposing weaknesses in current security means and practices 

or by narrowing the breach between what we i:now the analyst 

can do and the estimated security of our own systems Thus 

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progress is stimulated systems and techniques evolve and 

gradually the full capabilities inherent in them untold 

Secondly the closest possible coordination 1n the ap 

plication or security measures and 1n the collection and 

processing or signa~ intelligence has been recognized 

Until recently the United States Army had regarded these 

functions as being or primazay interest to the local. com 

mander Since Civil War days the War Department has made 

it its business to provide technically sound cryptographic 

aids and to prescr~be sound transmission practices 1n order 

to eliminate the most dangerous pitfalls but the application 

or these security measures rema.1ned a local matter throughout 

the Army As long as warfare remained fairly immobile the 

repercussions stemming from poor security practices and disci 

pline were usually localized the otfende~ himself paying the 

price for his indiscretions but as developments were made 

1n transportation and communications warfare became in 

creasingly fluid until today using the advanced techniques 

or signal intelligence it is possible to ferret out every 

broken thread in the enemy s mantle of security to gain an 

insight into his most secret preparations and to cripple h1m 

before he has a chance to strike or prepare an adequate 

de tens 

In intelligence the stream ot intercepted cODDnUllica 

tions which reed the analysts must be as complete as possible 

There must be no duplication of effort and the energy which 
is expended must be directed to that end which best serves 

the whole military establishment It has been stated on the 

highest authority that both the European campaign and opera 

tions in the Pacific were closely related in conception and 

timing to the 1ntell1gence derived trom the analysis of enemy 

comrrnm.4.cations Even so the service which was rendered by 

signal intelligence during the late war was tar 1.ess than it 

might have been 

While the feeling was growing 1n G-2 that signal intelli 

gence was the most impo~tant source ot information gaps in 

the picture which was being reconstructed by means ot it_, em 

phasized the urgent ne~essity tor the closest possible co 

ordinfl.tion in interception and processing This objective was 

not possible under the existing organization 

At the beginning of' World War II the overall respons1 

bilities tor signal intelligence and communication security 

were vested in the Signal Intelligence Service (later Signal 

security Agency and finally Aitmy Security Agency ) To meet 

their immediate needs however various commands bad organized 

signal intelligence and communication security units and re 

stricted their employment lor the most part to direct sup 

port of the missions o:f' the Commander to whom they were 

assigned The inevitable result was an irretrievable loss of 

much valuable intelligence through uncoordinated direction 

and numerous disparities 1n communication security practices 

which were quickly capitalized on by alert enemies 

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Signal Security Agency being a part of A:rmy Service 

Forces could not exercise operational or technical control 

over such organizations Neither were there co11DDon standards 

of training operating practices or discipline Thus it was 

possible for one organization to accomplish apparent lDiracles 

while another did well to earn its daily bread 

Perhaps one of the most obvious findings of World War II 

was that there is no line of demarkation that can be drawn 

between tactical and strategic signal intelligence This is 

due to three main factors First;r the inherent security 

of crn>tograph1c systems employed on various levels of com 

mend do not always follow a scale of increasing security 

Thus on a low level systems may be used which are compli 

cated out of all proportion to the nature of the traffic which 

they cover SeconclJP the so called high echelon systems 

which carry strategic intelligence frequently overlap into 

the province of intercept agencies which have as thetr 

primary mission the collection and processing of intelligence 

whic;h is of immediate tactical value to the command it serves 

In such circumstances this traffic must either be disregarded 

or if intercepted be passed up the chain of command to an 

agency which is capable of exploiting it to some advantage 

Thirdtr the actual processing of raw intelligence even of 

low level systems is frequently so complicated as to be 

beyond the capabilities of the field units This later factor 

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more than any other has made necessary a globe circling 

network of radio and wire links which are or have been 

exclusively devoted to .funneling a prodigious volume of raw 

intercept material to large intelligence establishments in 

rear areas or to Army Security Agency itself for processing 

During the War it was a normal occUl'ence for a message to 

be intercepted by a front line unit transmitted hal:fway 

around the world solved translated and returned to the 

proper field commander 1n time for action the whole circuit 

being completed within a matter of hours 

On the secUl'ity side of the pictUl'e mon1.tor1ng activi 

ties to check on correct cryptographic and transmission 

security practices were never as extensive as they might 

have been The old time reliance on net control stations to 

keep their subsidiary stations 1n line and to entorce a high 

caliber or operating discipline proved to be almost entirely 

unreliable The same could be said for the systems which had 

been instituted to bring to light the fUll extent of crypto 

graphic security violations by means of reports of viola 

tions voluntarily filed by receiving or originating head 

quarters These infractions though mainly small are 

present in such numbers where green or poorly trained crypto 

graphic personnel are involved that the hardiest cryptographic 

systems may be placed in serious jeopardy or suffer outright 

compromises Consequently various security monitoring organi 

zations were formed On the whole they did a tine job of 

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riding herd on the networks which they were assigned to watch. 

·In most cases, however, their efforts wer~ largely spent in 

staff information monitoring to the detriment o~ their 

security responsibilities. More9ver, virtually none of their....._ 

findings ever reached Signal Security Agency for study. To 

this day 1 no accurate estimate. can·be made of the total 

security of our communications during the late war. 

A careful consideratic:>n of the foregoing .factors led to 

the assumption of operational control of'Signal·Security 

Agency by the Assistant Chief of S_tarr 1 G-2 1 War Department 

General Staff, in December 194ll-. For a time, the Agency remained under the Chief Signal Officer for administration. 

Although this arrangement was an improvement in some· respects, 

the dual controls uii.der which the Agency functioned proved unsatisfactory. Finally, on 6 September 1945, a directi"ve was 

issued establishing the·Army Security Agency. ~he ·Agency 

was composed of all s·1gna.l intelligence and comnmn1cat1on 

securit_yestablishrnents, uriits, _and personnel of the Army~ 

Before we continue in the discussion of how the Army 

Security Agency is organized and how it f'unctions, let _us 

review some of the results which toqk place· during World 

War II t_o establish the importance of thefse activities. 

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bulldog perseverance and brilliant research never gave the 

machine the code name 'Magic' 

It was British who st used the wor 'Magic' as 

a sort ot cov rname tor the p oduct or fruit o certain 

highly spec! !zed operations which we now cal signal in 

tellisence o The when the 

U S Army ti st began putting out the highly s cret docu 

extremely l ted number of p ople t itself was 

the name 

'Magic' thus came to be used y certain V I P s who had 

access to t t document 

oncerning 

each trick divided into t o sections t there comes 

a section 1 The Ette t in which is ascribed what 

the audience sees and the llusion by whic the audience 

is mystif ie This is foll 

Method in hich is explain 

is produced in other words 

ot the trick is disclosed 

Ma:bshall are quivalent to 

letter 

labelled The 

or illusion 

secret or he !kn.ow how 

examples cite by General 

Effect 1n th glossary ot 

the magician Mr Devey onl refers in 

very general The Met od that is 

is produced 

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