REF ID:A66592 

EXTRACT FROM: LECTURE ON COMMUNICATION INTELLIGENCE - Given at Naval 

War College, 2o August 1948, New Port, Rhode Island by 

Captain J. N. Wenger 1 USN, Deputy Chief of Naval Communications for Supplementary Activities. 

Pages 46 through 59 

EXPLOITA1ION 

As prospective operating connnanders your primary concern with comnnmication intelligence is naturally its exploitation. A troublesome problem 

' 

arose in this connection during the War. It is worth mentioning here 

because you may be confronted with this problem at some later date. 

All knowledge and experience of war point to the necessity of 

exploiting every possible advantage. The temptation was, "therefore, 

naturally very great in the heat of battle to use communication intelligence whenever it was available. This led to carelessness which quickly 

threatened to jeopardize the source. 

In time of war t.he full value of communication intelligence cannot 

be realized unless operational use is made of it. However, when action 

is contemplated, as a result of this intelligence, the possibility of compromising the source must always be forne in mind and this danger weighed 

against the military advantage to be gained. A minor advantage is never 

alone sufficient ground for risking the loss of a communication intelligence source. 

The point of this principle is that most codes and ciphers are 

necessarily used over wide areas. A change by the enemy as a result of 

suspected compromise mcq therefore have far reaching consequences. A ; 

co:mmaIXler in seeking a minor advantage in one locality may deprive another 

commander elsewhere of a much greater advantage or deny the use of 
REF ID:A66592 

communication intelligence in a subsequent major operation. 

This indicates,, of course,, the great importance of coordinating 

operations,, where practicable,, with the intelligence situation. All example, 

with an odd twist,, of the consequences of one actual failure to do this 

will illustrate this point. Plans were made,, coordinated, and approved for 

a certain campaign in the southwest pacific. SubsequentJ.y the Air Force 

commander decided that use of a certain ad.di tional. airfield would be 

helpful,, and accordingly an attack was made on it by grolllld forces.: 

' Unfortunately the objective was overrun and an important Naval comniand 

ashore in the area was closely approached. Twelve hours later our forces 

realized the, .mistake and w.i thdrew,, leaving the headquarters intact, but 

meanwhile,, the Japanese in the excitement of the moment had erroneously 0 

reported all their codes and ciphers compromised. Swift and sweei>ing 

. changes were made by the J~panese. As a result, one of the most imi:>ortant 

operations of the Central Pacific, scheduled to coI1D11ence three weeks later, 

had to proceed without benefit of 1h e unusually complete intelligence 

which had been available just prior to this incident~ 

As a corollary to this basic principle of exploitation, cover measures 

should alwa.Y,S be taken in the use of communication intelligence. When the 

decision is made to take action based on it, studied effort must be made 

to ensure that such action cannot be attributed to communication intelli- ~. 

•, 

gence alone. When possible, such acti~n must always be preceded by suitable reconnaissance or deceptive measures. 

" BRIEFING 

Special care must also be used in briefing aviators or other personnel 

engaged in missions or duties which might readily subject them '00 capture 

0 
J 

REF ID:A66592 

by the enemy. Extreme pressure can be brought to bear upon such personnel 

if they fall into enemy hands, and it is both dangerous and uni' air to 

burden them with secrets which they do not absolutely require. 

Perhaps one actual incident will show the hazards involved. Communication intelligence was supplied to a task force commander, indicatilig the 

prospective movement of a certain Japanese force. The actual name of this 

force was included. Unfortunately, this latter informa.ti.bn was passed on 

to pilots who we~ sent out on searches for this force. Some of these 

pilots fell into enemy hands, and, un::ler severe pressure, revealed the 

details of their ..briefing. The Japanese were certain that the special 

name for their force could only have been obtained from their communications so they took evasive measures and thus denied us the advantage· that 

we had held. 

In this case, it was desirable that the task force commander have all 

available information regarding the expected enemy force, but his more 

~areful briefing of subordinates might have resulted in a far better.conclusion to this episode. The essential needs of the pilots could have been 

adequatell'." met by orde_ring them oo search a specified area, with at moat 

a general indication of the objective. 

A little ingenuity in haniling such problems will go far toward "Saving 

the goose tha. t lays the golden egg. Whenever it becomes essential for 

opera ti. onal. reasons to divulge an item of communica ti.on intelligence under 

circumstances involving any extra jeopardy to the source, the information 

must be so disguised that it cannot be traced oo the communication intelligence source alone. 

3 
REF ID:A66592 

COORDINATION WI'IH OPERATIONS 

There is another aspect of coordination between fleet operations am 

communication intelligence actiVi ties which should be mentioned. here. For 

most effective results the communication intelligence effort must be carefully oriented to give optimum coverage of operations in progress. A vast 

volume of communications has to be scanned each day. In order to give 

precedence to the material of current importance, it is essential that 

those controlling the production of intelligence are constantly and fully 

informed of the current si tuati.on. Moreover, this knowledge is essential 

to the proper interpretation of certain intercepted material. For, example, 

when a sudden rise in enemy traffic is noted, it may be a reaction to some 

strike by our own forces or i.t may be the prelude tO a strike by the enemy. 

Knowledge of our own movements permits correct interpretation accordingly. 

At the beginning of the war, our communication intelligence centers 

had great difficulty in obtaining information concerirl.ng operations of 

our own forces. Operating commanders naturally had the same concern about 

disclosing their secret plans as we had about our secret plans as we had 

about our secret successes. Some of their reluctance also arose from a 

misunderstanding of our problems. 

One actual example will illustrate the point •. During ibb.e Guadalcanal 

campaign, Japanese observers were reportin·g, in a tactical code, movements 

of our ships in and out of local harbors. In solving the code, it was 

readily determined that certain code groups represented ships of certain 

types, but we were not sure which types they were. If we could only know 

the actual movements of our forces, this question could be quickly set-tled~ 

When, however, a request was made for the information, it was denied on 

the grounds that it might influence .our guessing. We received the info:rma4 
REF ID:A66592 

tion only afte:c pointing out that positive identification of these code· 

groups for ship types, in these relatively unimportant, messages about our 

own movements, would enable us to be certain about them in far more 

important messages about enemy forces which might be intercepted. later. 

INTIDRATrON OF COMBAT AND INTELLIGENCE OPERATIONS. 

A curious si tua ti.on arose during the war which pointed to the neces~ 

sity for close integration of combat and intelligence openati.ons. As we 

captured enemy-held positions and sank enemy ships, the number of comm.unieating stations decreased correspondingly. Since C?ur ability to obtain 

communication intelligence was directly dependent upon the volume of enemy 

transmissions that could be intercepted, we .were confronted with the paradox of haVing our intelligence efforts threatened with defeat by our own 

combat successes. 

In the face of this difficulty, the aviators began to develop a great 

enthusiasm for knocking out radio stations,, thereby aggravating the si tua-

" 

ti.on. we were quick, therefore, in our appeals to restrain t.l-iem and 

fortunately succeeded in haVing their attention directed. to other targets 

before too much damage was done. 

Normally the disruption of enemy land-line and cable facilities is 

.... 

:much more effective than the destruction of radio stations. The former· 

will have three bene~ieial effects. First,, more enemy traffic will be 

driven to the air where it can be intercepted; second, this traffic will 

then have to be encoded thus creating addi t:i.onal difficulties; and, third, 

the additional load on the radio channels will probably tax their capacity, 

thereby seriously delaying, if' not actually preventing, the delivery of 

many messages. 
REF ID:A66592 

In connection with the integration of combat am intelligence operati.ons, it is especially important that intelligence officers understand 

the place of collateral information and captured docwnents in the production of communication intelligence. As in many other enterprises the more 

one puts in, the more Qne takes out. Much of the output, especially in 

the early stages of solution of cryptographic systems, is fragmentary.; 

It is frequently possible to fill in the gaps with collateral information, 

i.e. information from other sources, an:i thereby expedite solution. A 

' . great deal of the wrk, particularly in the field of traffic analysis, is 

pure deduction. Informa. tion from other sources is of tremendous help in 

arriving at correct interpretations. In many respects, traffic analysis 

is like dead reckoning in navigation. The errors are cumulative. tr, , 

from time to time, we are able to obtain a fix of reliable information. 

from some other source, be it a prisoner of war, a captured. docwnent, or 

' a reconnaissance photograph, we may be contradiction or confirmation check 

our course and proceed accordingly. 

CONCLUSION 

In the discussion which we have just had, I have tried to remove ,from 

' communication intelligence the aura of mystery and ro~e which popular 

writers are in the habit of attaching to this subject. My aim has been to 

present it to you as serious problem. It is such a complex and comprehensive one that, in the time allotted, I could give you only a glimps'e 

of the over-all picttire. But, I trust that you have seen how radio is. 

' 

truly a two-edged sword. Without it, command cannot function, but its 

improper use may bring disaster, as it did to our enemies, _or at least 

prevent • the achievement of surprise, as it sometimes did for us. As 

6 
.. ... ... REF ID:A66592 

somecme aptly said, nu you use radio at sea you are very likely to attract 

a lot of undesirab1e compal!\f". Perhaps this knoKl.edge may be hel.pf\il. to JOU 

at some later date. 

Above all, I hope ,ou have gained soae appreciation of the importan:e ot 

COllJDl\1Dica ti.on inte.1ligence to the future deteme ot our nation. . With the . 

advent ot 1oilg r~ air f'leets and guided: missiles which can strikB overwhsl mingly and without; warning,· it has became obvious that peacet!M 

intelligence is no l.anger Dl81'9~ a strategic protection, but a tactical one ' I 

as well in the most literal sense. The devastation or t.l'l8 first atomic bamb 

Cl"7Stallized this thought as nothing else could have dona. It is now apparent, 

with a. special clarity and urgeJ1:7, that campletaly effective intelligence is 

imperative tor the safety ot our country, and effective intelligence, if' the 

example of World war II can be accepted as a criterion, means in ·a large 

meaBU1"8 coDIDlUllica ti on intell1gence. 

If our Nation is to be protected in the tutw:e, anticipation or attack 

al.one 1s not enough, becauae attack miq' be too overwhsl.miJJg to cdmbat. In 

these tiDB s of total war, f!IVeey f'ie_ld ot natloml enterprise mmt be 

scntiD:lzed tar the slightest signs that may -.rn ot hostilities.. Troubles 

' 

llUSt be detected betare they· can gain the mClll8Dtum that leads to war. This 

is the mission ot intelligence, and espeoiall7 of comnunication intelligence. 

Intelligence is our real first lina ot defense. The smaller our militar{ 

establishment, the eater must be oar intelligence safeguards. ' 

We are not alone :In appreciating the fv:ture sign.iticaace of cOlllllll1Dlication 

intel.ligeme. otller natio:m are taking increased msasUl"es tor seCUl"it7 and., in 

conseqmme, our ditficul.t.:les promise 'ID increase traae·moual.7. In closing, 

7 
91 • r '• REF ID:A66592 

•TI, therefore, emphasize again the importance of avoiding ur.mecesSU7 

discussion ot 11bat bas been reveal.ed. to -rou todaT. The Hav Departm.m1; bas 

refused to cont:l1.'lll ~ d9DJ" an)" press disclosures, and it is most advisa~ 

that this policy be supported by all who know the truth. 

May I t:hanlt 1011 for your VefrT Id.Di attention. 

B 
REF ID:A66592 

EXTRACT FROM: LECTURE ON OOMMUNICATION INTELLIGENCE - Given at Naval. 

War College,, 20 August 1948,, New Port,, Rhode Island 

by Captain J. N. Wenger,, USN,, Deputy Chief of Naval 

Communications for Supplementary Ac ti vi ti.es • 

..g' 

Page 25 ~ugh Jt 

"YAMAMOTO 

My next slide (4) illustrates the part played by communication 

intelligence in one of "the most dramatic episodes or the war - the ambush 

of Admiral Yamamoto. The details of this event have been widely publicized,, 

but a few notes on the intelligence aspects of it may be of interest. The 

essential facts are shown on this slide. 

A chronology of events associated with this affair follows. All times 

are minus 9. 

APRIL 14,, 1943 

1. At 1¢¢8,, the Pearl Harbor c. I. Unit sent out a despatch to 

CINCPAC,, COMSOPAC, and COM7'1HFLT containing a fragmentar,r translation of 

a Japanese message,, dated 17.5.5/I 13 April 1943, from£!!!.£ SOUTHEASTERN 

~ FLEET to several addressees,, including CO}IDR. BAI.LALE GARRISON: 

On 18 April £!!Q COMBINED FLEET will ----

as follows: Ballale Island • --------- Comment by FRUPAC: Tb.is is probably a schedule of inspection 

by £IN.£ COMBINED~· The :message lacks additives, but work 

will be continued. on it. 

APRIL l.S', 1943 

2. At 15¢41¢/l and 15~6.57/l, the Pearl Harbor and Washington C.I. 

Units sent out more complete translations of the same message. These 

are summarized on the slide. 
REF ID:A66592 

At ll49/I, CINCPAC notified task force commanders in the Pacific: 

At~ (~~/I) on 18 April, YAMAMOTO himself, via bomber 

escorted by six fighters, will arrive from RA.BAUL in the BALLALESHORTLAND AREA. He will leave KAHILI at 16¢¢ the same day to 

return to RA.BAUL. All dates and times are 11111. In case of 

bad weather, the trip will be postponed until 19 April. 

At 1543/l, FRUMEr.. disseminated. the translation of another Japanese 

message, dated 1221/l April 14, from &\BAUL ~ FORCE to an unidentified 

addressee, wherein reference was made to "the special visit of YAMAMOTO", 

and "in view of the situation regarding air attacks on the postn, certain 

precautionary arrangements were requested, including the moVing of the 

rrpostn to a new loca ti.on. 

APRIL_l8, 1943 

At ¢5¢5 and ¢535/1 April 18th, a Jap plane· was noted by FRUPAC 

originating encoded weather reports. FRUPAC commented (in his 181926Z 

(19¢426/1)) t.ha t this was an •unusual time for Nip plane weather mission". 

At almost exactly the predicted time 1 the enemy planes were sighted 

approaching BALI.ALE, arxl at 1129/l, a paraphrased message of COMAIRSOLS 

reported as follows: 

''Major J. William Mitchel, USAFF 1 led P-.38 ts into KAHILI AREA.. 

Two bombers,; escorted by six zero's fiying in close formation, 

were shot down about ¢73¢/1. One other bomber shot down was 

believed to be on test flight. n 

MAY 21, 1943 

At 15,e}.fl/l May 21st, the Japanese Navy Department originated an ALNAV 1 

in plain text, reading in part as foll011Ts: 

2 
REF ID:A66592 

"The Commander-in-Chief' or the COMBINED FLEET, ADMIRAL ISOROKU 

YAMAMOTO, died an heroic death in April or this year in air 

combat with the enemy lirl.le directing operations from a 

forward position." 

I might say in comment that this is an excellent example or highly 

effective teamW"Ork between the Anny and Navy in the war. In this case,, 

~the Navy obtained the intelligence and set the trap; the Anny sprang it. 

TRAFF! C ANALYSIS 

My final example in the Pacific War illustrates the value of traf'tic 

analysis. This slide (5) contains headings of a series of messages 

actually transmitted by the Japanese and received by us. By _means ot 

these headings, a.Di without knowledge of the contents or the texts, we 

were able to determi.De very accuratel7 the movements of two major units 

of the Japanese Navy, at a time when the information was not obtainable 

otherwise. 

All call signs in the headings are in their enciphered f onn and the 

identification or each, as obtained b7 reduction or the cipher, is shown 

immediately above it. 

- On 21 April 19h4 a Naval dispatch was intercepted from KURE radio 

station. This is represented on the slide as heading "A". 

COLL CALL 

SO HD RI 

KURE RADIO 

DE YASIKO !!Q.191 TIKA 

SAEKI AIR STA 

TIMAMI6 

SUB CHASER SS SAEKI DEF FOR 

TO HI SU NIHOKO 

COMMINDIV 54 

l!Sl1E - TUHO 

BB 

~ 

YAMATO CA MAYA// 

kU I 911 

GRAND SURESOO IMP HQ NAV 

SEC 

KO NI 5 KA TI 2 

2l.14l; (TEXT) 

BUNGO CHAI 

DEi' 

ISUO HA 

3 

w8l 

COMMDIDIV 3 

KURE DEF 

COMDR 

KA NI 1 
REF ID:A66592 

From the associa ti.on of the addresses it appears that this is a 

dispatch from the commander of the ~DEFENSE FORCES notifying the 

defenses and patrols of~ HARBOR and BUNGO CHANNEL that :triendJ.7 ships 

are to pass through the defense area. The question as to which ships tbey 

are is answered by the inclusion of the call signs for the battleship 

YAMATO and the heavy cruiser MAYA. That the ships were leaving port 

rather than entering is determined by two circumstances. First, previous 

information had definitely placed both ships at KURE, and, second, the 

dispatch was transm:i tted on the KURE local circuit. Previous experience 

indicated that tilis dispatch would have been delivered via the TOKYO high 

frequency broadcast if these S'lips had been approaching KURE. 

Accordingly, it was reported to the commander-in-chi et that the 

battleship YAMATO and the heavy cruiser !!!:! were about to sortie through 

the BUNGO channel. No prediction as to destination was then possible. 

On 22 April 1944, another dispatch pertaining to these ships was 

intercepted from~ radio stations. This is heading "B" on the slide. 

As the call signs for mobile uni ts were changed daily you will note that 

they differ from those appearing in heading "A". 

(See YAMATO and MAYA) 

COLL CALL 

SO RU R.! 

KURE RADIO 

YA SI KO 

ITO lUl - ONA W78 

DE 

MANILA TPll 

DEPT 

TI //NI RU NA TUHO 

CINC .3RD SO 

EX FLT 

RE MU 8 

2216li4 (TEXT) 

BB YAMATO 

MU KI .3 

4 

KURE TPN 

DEPT 

KI"""ft'""WA 

CA MA.YA 

YO RE 1 // 

BT 
REF ID:A66592 

This is a dispatch from the KURE transportation office to the corres- - ponding office in MANILA aDi evidently concerns a shipment from~ to 

MANILA which is apparentJ.7 on board the two ships. But now we haTe intormatl.on as to their destination. There is additional. evidence that the7 

have left KURE (delivery to the t110 being accomplished by KURE radio) but - - are still in the immediate vicinity of,!!.! because the delivery was b7 a 

frequency used for local commwli.cati.ons. 

Accordingly it was reported to the cominallier-in-chief' that the YAMATO 

and ~ which had lett ~ on the dq bef'ore were headed toward MANILA.. 

2.3 April another dispatch was intercepted, this time from TAKAO (on 

FORMOSA) radio station. This is shown on the slide as heading ncn. 

BB YAMATO 

mJ KU NA 

SINGAPORE 

fPN DEP 

TI II NO A 1 

CINC lST 

MOBILE FLEET 

II RO 0 J. 

231423 (TEXT) 

DE 

TUHO 

CINC 

TAKAO RADIO 

TA HI 0 

YAMATO 

KI A 4 

2ND FLEET 

SU NA 4 

RO NA 

DD 

IUKIKAZE 

HE Tl 6 

CINC 

.3RD FLEET 

SE MA 2 HA 

w58 

DD 

SHIMAKAZE 

0 0 2 

KURE 

TPN 

KI TI WA 

This secom dispatch f'rom the KURE transportation department now - indicates that at least part of the shipment on board the YAMATO is 

destined for SINGAPORE; hence the YAMATO is only stopping at MANILA but 

till continue on to SINGAPORE. Also the direct delivery by ~ radio 

indicates that the ship has now arrived in the FORMOSA area. As the ship 

departed on the 21st, this was a logical conclusion. We also pick up the 

fact that she is being escorted. by at least two destroyers (YUKIKAZE"; and 

SHIMAKAZE). Other dispatches from the ~ transportation department 
REF ID:A66592 

carried similar headings which confirmed the tacts drawn from this area. 

Incidentally, it is worth noting that this movement was probabl7 

conducted in great secrecy by the Operational Commander Afioat only to 

have it given away completely by a shore administrative office. 

Time does not permit us ix> pursue this analysis, but the ships movements were predicted am followed to MANILA and SINGAPORE in this mamier. 

The strategic si tuati.on was such that immediate advantage could not be 

taken of it but at least the whereabouts of tw import.ant enemy units was 

accurately known, as was later fully confirmed. 

THE ATLANTIC WAR 

we shall now tum to the A tJ.antic. There our problem WfS of a different nature. We had to rely upon means other than cr,yptanalysis to determine the location am. movement of enemy forces. Radar and sonar had 

demonstrated tremendous potentialities as aids in the U-boat hunt, but 

these aids had to be brought within their efi'ecti ve range before they could. 

be useful. It was here that communication intelligence supplied the 

necessary link. 

By means or direction finders the problem of search was vastly 

simplified_, and aircraft and surface vessels were enabled. to confine their 

• 

operati..ons to profitable areas. Conversely it was possible to divert the 

convoys from those areas where the probability of attack was high. Success 

against the German submarines was thus in the end primarily the result of 

the highly efficient coordination of communication intelligence, radar, 

sonar, aircraft and surface escorts. From the time this coordination 

became e.t.fecti. ve, the enemy• s submarine losses began to mount sharply and 

our losses in the Atlantic showed a marked and steady decline. 

6 
REF ID:A66592 

In order for direction finder bearings to be use.ful they had to be 

collected at operational centers in Washington,, London,, and Ottawa in a 

matter of minutes. This required the establishment or a nash communication system covering the entire Atlantic area, by means of which controlling stations covering the radio spectrum could alert the D/F stations to the 

desired transmission. The submarines were alive to the effectiveness of 

our direction finders and resorted to all sorts of measures to defeat them, 

including extremely short t.ransmissions whicli had to be identified and 

intercepted in a matter of secoms. Despite these difficulties, it was 

possible in the latter months of the war to obtain and plot bearings from 

practically all of the stations in the Atlantic within a matter of 15 or 

2¢ minutes. About the middle of the war shipboard direction finders had 

become sufficiently workable to permit their use by forces afloat. These 

shipboard equipments were then coordinated with the shore direction timer 

system am the general effectiveness of the network was somewhat iDq?roved. 

The next three slides (6), (7) and (8) are actual examples of three 

daily situation plots forty-eight hours apart. The black dots represent 

direction finder fixes on U-boat radio transmissions. As you can see, the 

dots show clearly the active submarine operating areas. These situation 

plots are of particular interest because they show the developments of 

two wolf-pack attacks. These are clearly indicated by the concentrations 

of dots in the latter two plots. 

D/F PROBLEMS 

As important as the direction fimer proved to be, its practical 

application presented a number of formidable technical. problems. Fixing 

a position was more an art than a science. The vagaries of wave propaga7 
' . REF ID:A66592 

ti.on and the presence of instrumental and personal errors made it 

impossible to rely on merely a few bearings. For example, here is an 

actual and typical plot of bearings in the Atlantic (9). Note the area 

covered by the intersections as compared to nearby land masses, such as 

Cuba. 

To overcome such difticul ti.es 1 a very large and extensive direction 

fimer net was established. At its peak the Atlantic net contained Sl 

stations, or which 17 were American, 23 British, and 11 Canadian. My 

next slide (10) shows their locations. 

Special systems or evaluating the bearings from these stations were 

evolved so that the resul. ts could be brought w.i thin practical. limits. 

8