-.-.--- ~ ... ---- --------------------------

REF ID:A67329 

- . ~. -· .. 

PRELIMmARY HISTORICAL REPORT ON THE SOLUTION OF THE "B" MACHINE 

Part I - Technical 

1. In the latter part of 1938, messages appeared in a special 

secret Japanese cipher giving the authorization for travel for a 

"Communications Expert" named Okamoto, in order that he might put 

into service certain cryptographic paraphenalia termed by the 

Japanese diplomatic offices as the Type 11B" cipher ma.chine. This 

machine was to replace the then currently used Type "An ma.chine for 

highly secret communications among the important Japanese embassiesl 

throughout the world and the Foreign Office in Tokyo. On February 

19, 1939, a message bearing the date of origin as February 18, 1939, 

in superenciphered code (K-1 transposed and enciphered by special 

A-ma.chine procedure} was intercepted and was found to give the 

effective date of the initiation of the B-ma.chine as February 20, 

1939. The A-ma.chine was still to be used by all holder_s for certain 

1 Washington, Berlin, London, Paris, Moscow, Rome, Geneva, Brussels, 

Ankara, Shanghai, and Peking. 

Declassified and approved for release by NSA on 09-10-2013 pursuantto E .0. 1352a 

• -·' • I • • •" ' ' ' '•• • i 
REF ID:A67329 . . . . . ... . .. . ~ 

classes of communication. 

2. Among the first messages received after the effective date 

of the B-machine were three messages, originating in Warsaw, which 

had a new type of indicator instead of the normal 11A11 type indicator. 

EKamination of these messages showed that they were definitely not 

"A" type messages, but due to the fact that six of the twenty-six 

letters appearing in the text of the messages were abnormally high 

(as they would have been had the A-machine been used for their 

encipherment) it was assumed that the messages were prepared by 

the B-machine and that it was a modification of the basic A-machine. 

Further intercepts tended to corroborate this theory. The A-machine 

was continued in regular use at Hsink.ing and Shanghai and very 

occasionally (apparently when the B-machine was out of commission) 

the A-machine continued to be employed at the places which had been 

provided with B-machines. 

3. .After a brief study it was confirmed that the di vision of 

the letters into two categories (one group of six letters and another 

2 
REF ID:A67329 

group of twenty letters) which was the basis of the cryptographic 

treatment in the A-machine was retained in the B-machine but with 

a very important change. Whereas in the A-machine the 6 letters 

comprising the "6 1 s" as well as the 20 comprising the 11 20's 11 were 

enciphered by means of what had been deduced as being a rotating 

commutator, whose stepping was controlled by a break wheel of 47 

positions with certain skips in the cycle (the commutator could 

advance l, 2 or 3 steps at a time), in the B-ma.chine the "6 1 s" 

were enciphered by means of a series of 25 heterogeneous and 

differently mixed alphabets which were constant in their nature 

and cyclic repetition. These 25 alphabets were merely a carefully 

selected set of 25 of the possible 720 permutations or transpositions 

of 6 elements taken 6 at a time, and a deciphering chart or "development n was constructed to correspond with these 25 permutations. 

This chart was revised and corrected from day to day witil it became 

certain that all its elements were absolutely correct. 

3 
.REF. ID:A67329 

4. This having been accomplished (by April 10, 1939), it 

became possible, as a result of crypta.na.lytic technique elaborated 

for the purpose, to decipher the 11 61s" in practically every message 

of any considerable length in the B-machine • It was found that so 

far as the 11 61 s" between two messages with unlike indicators were 

concerned, the only difference between one indicator and another 

was the starting point in the cycle of 25 alphabets. There were 

120 different indicators but only 25 different starting points, 

so that four (in certain cases, five) different indicators 

represented the same starting point. 

5. When the "6 1 s 11 in a given message were deciphered, the 

plain text values of cipher letters scattered here and there 

throughout the text became available, so that the skeletons of 

words and phrases offered themselves for completion by the 

ingenuity and the imagination of the cryptanalyst. For example, 

suppose that on a given day the 6 letters forming the "6 1 sn were 

E Q A D R H and the following text was at hand: 

4 
REF ID:A67329 

Cipher: BRAXEFQCEVQOOXHECFDLNHQRVQPPLCERP 

Plain: HE A A E E ER E REQ E HA 

It is not difficult to imagine that the missing letters are those 

shown below: 

Cipher: 

Plain: 

BRAXEFQCEVQOOXHECFDLNHQRVQPPLCERP. 

!HE~A~A!E~E~~YER!~E!!REQ~E~!~!HAT. 

In this process of filling in the plain text val.ues of the "20's 11 

the cryptanalyst could be guided only by two things: (l) the positions 

and identities of the deciphered "6 1 s 11 and (2) the context. For it 

speedily became apparent that any cryptographic relationship between 

the plain text and the constantly-shifting cipher text values in the 

case of the letters constituting the group of "20's" had been most 

carefully eliminated, disguised, or suppressed. This fact corroborated 

the conclusion drawn from all statistical and analytical tests made 

on the cipher texts of the various messages studied. 

6. The process of filling in the plain text values of the 11 20's 11 

was therefore, as a rule, a very difficult matter, depending usually 

upon the particular assortment of letters constituting the 11 61 s". 

If the text was in Japanese there was, in addition to the difficulty 

5 
REF ID:A67329 

inherent in that language itself, the added perturbation occasioned 

by the fact that the Japanese Foreign Office had, on May l, 1939, 

instituted a species of "Phillips Code" in connection with their use 

of the B-ma.chine, with a long series of arbitrary letters and 

abbreviations standing for numbers, punctuation signs, and frequently 

used combinations of letters, syllables, words, and sometimes complete phrases. For instance, the combination C F C represents 

period; C C F represents paragraph; the single letter L (not normally 

used in Japanese) represents the diphthong ai; X represents ~; P 

represents ni; V represents long U; Q T Q represents Arita (shi) 

itashi tashi; BK W represents Beikoku (. United States); T KW 

represents TeikokuseifU (=Japanese Government); SN W represents 

Sukunak.arazu, etc., etc. The difficulties introduced by this 

abbreviated or rather code writing al.one were quite staggering as 

well as aggravating, for often the "text" even when finally reconstructed appeared more like code or a random assortment of letters 

6 
Cipher: 

Plain: 

REF ID:A67329 

than plain text.2 For the reconstruction of' such text, the services 

of' the Japanese experts were absolutely essential, and the work went 

very slowly not only because of' its difficulty, but also because the 

services of' these translators were available only a small part of' 

the time when the traffic for the daily "Bulletin" permitted, which 

was quite seldom. However, occasionally it was found, after the 

11 6 1 s,. in a given message had been deciphered, that these letters 

2 A typical example of' the sort of' "text" usually found at the begimiing of' messages is the following: 

FGPXP IXUDB DGECZ LBLNU ZQOQH YNMRQ ARJOP 

XFCGJ WFOVD DNOBB FYXFO CFYLC CFMSG TSJVR 

DE I LO AXPPP LIGDK ZPGRA 

KHIFI CGURV FELBK WTLSI 

The correct grouping of' letters and the interpretation of' the foregoing "plain text" is as follows: 

XFC -Dai -go 

G J W = 15 

F 0 V = Open parenthesis 

DD 2 

N O = "of' 11 (Jap. plain text 

partic1e possessive) 

B B = l 

F Y X - Close parenthesis 

F 0 C = Gokuhi ( .. Secret) 

F Y L = Kancho f'ugo atukai 

C C F = Shin sho (: paragraph) 

M S = 3 

G T S .. Getsu (month) 

J V R K = J\lroku (= 16th) 

H I = Japanese word for ua..ayn 

F I C = Begin ka.na spelling 

G U R V • GurU (. Grew) 

F E L = Close ka.na spelling 

BK W : Beikoku (. U. S.} 

T L S I = Taishi ( = Ambassador) 

In rwming language, the message begins as follows: "Number 15 (part 

l of 2 parts) Secret, to be kept within the Department paragraph On 

March 16th the American Ambassador, Grewn, etc • 

7 
REF ID:A67329 

and their distribution throughout the message gave good indications 

of the presence, in whole or in part in the message, of normal 

English text. In such cases, the "guessingir process was likely to 

be considerably easier because of the absence of abbreviations 

(except for punctuation signs, in which case these were a help), 

because of the cryptanalyst's greater familiarity with the la.ngu.age, 

and because of the availability of the services of a larger number 

of workers. It happened that in several cases, after a few words 

had thus been obtained by pure "guessing", a clue was afforded 

as to the general nature of the message and this led to a frantic 

search for a complete document which might be available either in 

our own files or in the files of other government agencies. One 

case was found in which the ~-machine message contained a paraphrased 

version of a message which had been transmitted in K-1 code. Advantage 

was, of course, immediately taken of this circumstance but the entire 

text of the B-machine message could never be reconstructed from the 

8 
REF ID:A67329 

.. . . - . -·-·· ... : ... 

paraphrased K-1 version, possibly because of the excellent paraphrasing, 

possibly because of the presence of abbreviations, possibly because 

of both. Certain English text messages, however, were reconstructed, 

some of them to the extent of 90-951>, because the documents being 

quoted in the messages were fortunately located and obtained, most 

often through the cooperation and good offices of G-2. 

7. In all, the plain texts for parts of some 15 fairly lengthy 

messages were obtained by the methods indicated above, and these 

were subjected to most intensive and exhaustive cryptanalytic studies. 

To the consternation of the cryptanalysts, it was found that not only 

was there a complete and absolute absence of any causal repetitions 

within any single message, no matter how long, or between two messages 

with different indicators on the same day, but also that when 

repetitions of three, or occasionally four, cipher letters were found, 

these never represented the same plain text. In fact, a statistical 

calculation gave the astonishing result that the number of repetitions 

actually present in these cz:yptograms was less than the number to be 

9 
REF-ID:A67329 

expected had the letters comprising them been drawn at random out 

of a hat! Apparently, the machine had with malicious intent - but 

brilliantly - been constructed to suppress all plain text repetition. 

Nevertheless, the cryptanalysts had a feeling that this very circumstance would, in the final analysis, prove to be the "undoing" of the 

system and mechanism. And so it turned out~ 

8. In all the foregoing studies, several factors stood out. 

First, the basic law underlying the B-machine was of such character 

that the ciphering mechanisms seemed to start from certain initial 

settings and to progress absolutely methodically without cyclic 

repetition of any sort, straight through to the end of the messages, 

the longest of which for which plain text had been recovered comprised 

over 11 500 letters. Secondly, two identical plain-text letters in 

sequence could never be represented by two identical cipher-text 

letters; nor could two identical plain text letters 26 letters apart 

be identically enciphered. This phenomenon which was termed 

"suppression of duplicate encipherments at the lst and 26th intervals" 

10 
REF ID:A67329 

formed the subject of long and arduous study, fruitless experimentation 

and much discussion. Thirdly, two messages with identical indicators 

on the same day appeared to be identically enciphered, and on direct 

superimposition showed themselves to be monoalphabetic within columns, 

but with the monoalphabets constantly, irregularly and unpredictably 

shifting from column to column. Fourthly, two messages with identical 

indicators on different days (different plugboard arrangements into 

the machine) were absolutely different. Fifthly, two messages with 

different indicators on the same day (same plugboard arrangement) 

were absolutely different and showed no cryptographic similarities 

whatsoever. Sixthly, in each line of 26 letters, two identical 

letters could be identically enciphered except at the 1st interval., 

that is, identical encipherments could, and often did, occur within 

a line of 26 letters at all intervals, except at the 1st interval, 

although this phenomenon was rare at the 2d, 3d, 4th and 5th intervals. 

9. At the same time as the foregoing phenomena were being 

studied, intensive research was continued in an endeavor to establish 

11·. 
REF ID:A67329 

primary or basic cipher sequences of the nature of those usually · 

found in cryptographs with rotating commutators, rotors, and the 

like, such as in the Hebern and Enigma cryptographs, our M-134, etc. 

For it was inconceivable that the machine employed a multiplicity 

of non-repeating keys of lengths corresponding to the lengths of the 

messages and, moreover, theoretical considerations eliminated the 

possibility that running keys were being used. Somewhere, somehow, 

the existence of cyclically repeating keys or sequences must be 

uncovered before solution co7ld be effected. But all efforts to 

disclose the presence of cyclically repeating sequences were fruitless. 

In one and only one case was there found even the slightest hint of 

such sequences as were being sought. In a certain English text 

message the letter E was found to be represented by Q, 26 letters 

away another E was found to be represented by Y, and again 26 letters 

away another E was found to be represented by V, making the sequence 

QYV; in the very same message the same trigraph Q Y V was found to 

represent three E's similarly spaced. Attempts to add to this Q Y V 

12 
RE.F ID :A67329 

sequence were absolutely unavailing. In this long exhaustive and 

tedious search for repeated sequences or partially repeated sequences 

much labor and energy was expended but it was realized that the 

difficulty was probably due to the paucity of the text, despite 

the number and length of the individual messages available for study 

and for which the plain text had been reconstructed. It became 

apparent that what would be necessary was to obtain, by some manner 

or other, several messages in the same indicator and on the same 

day, or else to convert several messages with the same indicator 

but on different days to the same base, before even the existence 

of such cyclic sequences could be detected. 

10. In all the thousand or more messages on hand there were 

but a mere baker's half dozen or so cases where there were two 

messages on the same day and in the same indicator. More than two 

had never been found and this was to be expected in a system with 

120 different indicators available for selection each day. In one 

case of this rare phenomenon the plain text for one of the two 

13 
REF ·ID :A6·7329 

messages was available but very little could be done even then as 

regards the solution of the other member of this pair of messages. 

For such a method of attack at least 20-25 messages all in the same 

indicator and on the same day would be necessary and this was of 

course recognized as a perfectly hopeless expectation. There 

remained the possibility of converting several messages with the 

same indicator but on different days to the same base and while 

this method of attack looked extremely difficult it did not appear 

hopeless. 

ll. A method for this conversion to the same base was developed 

and was termed 11 the identification of homologs." That is, an attempt 

was to be ma.de to establish that a given letter on a certain day 

and another letter on a different day were treated in an absolutely 

identical or, more accurately speaking, homologous manner by the 

machine when set to the same indicator. This conversion process 

is too involved to explain in this report but suffice it to say 

that difficult though it is, it was successful in two cases. One 

14 
REF ID:A67329 

of these yielded a set of 6 messages, all in indicator 59173, which 

could all be reduced to the same base • These formed the crucial set 

of messages from the study of which success in solution of the machine 

was finally achieved. 

12. Distribution tables of the letters constituting the text of 

these six messages were made. It should be stated that in four of 

these six crucial messages only fragments of plain text had been 

reconstructed, here and there; the complete or nearly complete 

plain texts of only two of these six messages had been reconstructed. 

However, enough data were accumulated from these two completely and 

and the other partially reconstructed messages to yield distribution 

tables which, on careful examination, disclosed the presence of 

repeated sequences, here and there. This, on September 20, l94o, 

at about 2:00 P.M., was the very first indication that a successful 

attack might be possible. There was much excitement at this first 

glimmer of light upon a subject that had for so many months been 

shrouded in complete darkness and regarded occasionally with some 

15 
REF ID:A67329 

discouragement. The nature of the distribution tables referred to 

is also too involved to explain in this report, but sUffice it to 

indicate that they showed certain symmetries between the successive 

cipher equivalents of a given plain-text letter and the successive 

appearances of that plain-text letter in the cryptographic text. 

13. As soon as the existence of cyclic or symmetric sequences 

became clear, attempts were ma.de to uncover complete basic sequences 

of the type theoretically predicted. But many conflicts and inconsistencies soon developed, due to the fact that the cryptographic 

laws underlying the shifting from sequence to sequence was still 

unknown. Concurrently with the work connected ·with straightening 

out and removing inconsistencies in these reconstructed basic sequences 

ran the work of uncovering the cryptographic laws referred to, and 

very soon the general nature of the latter became quite clear. All 

efforts were concentrated upon the development of the specific laws 

and specific basic sequences applicable to the indicator under study, 

viz, 59173, with a view to uncovering all the cryptographic phenomena 

16 
REF ID:A67329 

in this case and then searching for analogous phenomena in the case 

of other indicators. Certain qualified personnel from other sections 

were brought in to assist, and a considerable amount of night work 

was found desirable in order to push this study to completion at 

the earliest possible moment. 

14. By September 27, just one week later, the work had progressed 

to a point where it became possible to hand in two translations 

representing the very first "solutionn to the B-machine. Two messages 

of recent dates, both in the 59173 indicator, were available and were 

solved by applying the principles of solution by homologs, guided 

by the aid of the reconstructed basic sequences. It was all the more 

gratifying that this could be done on the very day that announcement 

was made of the signing of the Tripartite Agreement among Germany, 

Italy, and Japan. 

15. Much work remained to be done, however, since only the data 

applicable to but one out of the whole set of 120 indicators were at 

hand. To solve the remaining 119 indicators appeared still to present 

17 
REF ID:A67329 

quite a large problem.· These solutions consist of finding the initial 

settings of three 20-level rotary, electrical cryptographic elements 

of 25 points each, and finding the order in which these three elements 

a.re brought into play within each indicator system. With but little 

slackening of the pace set by the personnel themselves, work has 

progressed with vigor and at this moment solutions for over one-third 

of the 120 indicators a.re available. 

16. As to the mechanics of the B-machine, naturally the basic 

principles of its construction and operation were deduced from the 

cryptographic phenomena observable in the messages, and immediately 

plans were initiated for the construction of a.n equivalent machine 

for our purposes. Orders for the material for 2 fully automatic 

machines were placed and expedited. While awaiting the arrival 

of this materiel a hand-operated machine was designed by personnel 

of the J-B section, constructed by them, and is at this writing 

being used to assist in the decipherment of messages. Basically, 

the B-machine consists of 13 rotary, 6-level, 25-point, switches 

18 
REF ID:A67329 

of the type employed in automatic telephony. One of these 13 switches 

controls the encipherment of the "6 1 sc' and it goes through the same 

25-point cycle over and over again as many times as is necessary to 

encipher the messages. It has 150 cross-connections, which, as stated 

above, had been established long ago. As to the "20' s 11 , these are 

enciphered by ~ans of 3 banks of 4 switches each, each bank having 

500 cross-connections, making a total of 1,500 sub-circuits available 

for the encipherment of any given letter. The arrangements for 

advancing these switches is such that for a given indicator, say 

20846, bank number 3 steps continuously, bank number 2 steps once 

for every 25 steps of bank number 3, and bank number l steps once 

for every 625 steps of bank number 3. This type of motion has been 

designated as a "321" motion. For another indicator the order of 

this stepping may be different and in all there appear to be 6 

different types of stepping: 1-2-3, 1-3-2, 2-1-3, 2-3-1, 3-1-2, 

and 3-2-1. Although there are 120 different indicators there are 

only 6 different types of motion or stepping of the three ciphering 

19 
REF ID:A67329 

switches, so that it appears that each type of motion is represented 

by 20 different indicators. What differentiates one indicator from 

another within such a set of 20 indicators are the relative starting 

points within the three banks of switches. These starting points 

appear to have been very carefully selected so as to preclude or 

reduce the possibility of "overlaps,n that is, the production of 

two messages which in whole or in pa.rt have been enciphered by 

identical keying elements in identical sequence. Once these 

factors concerning all indicators have been established, and our 

ma.chine is in operation, the reading of B-machine messages resolves 

itself into the establishment of the daily plugboard arrangement, · 

that is, the order and identity of the wires leading from the keyboard into the cr;yptograph and thence out of the cryptograph into 

the printing unit. Cryptanalytic procedures for this purpose have 

alrea.d:y been established and tested, so that this should not be a 

serious problem. Given a long message or several short ones of the 

same date, solution should be possible in an expeditious manner. 

20 
REF ID:A67329 

17. The solution of the B-machine has, as a concomitant, thrown 

considerable light upon the mechanism of the A-machine with the result 

that our present A-machine will be modified in the light of these 

discoveries and will be ma.de more efficient. The whole situation 

with respect to the cipher ma.chines employed by the Japanese Foreign 

Office now appears to be integrated into a consistent scheme of 

development from its earliest and simplest beginnings, about 1930, 

to its present quite complex form. Problems concerning the A-machine 

and questions for which logical and "reasonableu answers could not 

be found are now explainable on the simple grounds of the type of 

cryptographic mechanism employed in the earlier machines, which 

seems to be the rotary switch used in automatic tel.ephony, rather 

than the revol.ving commutator employed in our present A-machine. 

******** 

Pa.rt II. Credits 

18. The successful. solution of the B-machine is the culmination 

of 18 months of intensive study by a group of cryptanalysts and 

assistants working as a harmonious, well-coordinated and cooperative 

21 
REF ID:A67329 

team. Only by such cooperation and close collaboration of all 

concerned could the solution possibly have been reached, and the name 

of no one person can be selected as deserving of the major portion 

of credit for this achievement. The parts played by the individual 

members of the team may, however, be indicated. 

19. The specific direction and coordination of all studies on 

this project was the joint work of Cryptanalyst Frank. B. Rowlett 

and Assistant Cryptanalyst Robert o. Ferner. Their indefatigable 

labors and brilliant analytical work testify and are a credit to 

their cryptanalytic skill, training and experience. To their joint 

direction and efforts are due the extremely fruitful analysis of 

the cryptographic mechanics underlying the operation of the B-machine 

as a whole, the theory of its operation, and the development and 

solution of the n6 1 s" at any early date in these studies. They 

were also extremely active in pushing the solution to a successful 

conclusion by organizing and directing the reconstruction of the 

developments or wirings of the switches for the n20 1 s 11 • Junior 

22 
.REF .ID ~A6.7329 

Cryptanal.\Ysts Genevieve M. Grotjan, Albert w. Small, and Samuels. 

Snyder did most excellent work in recovering the 1t6 1 s" during many 

monthsaf apparentl.\Y hopeless e:f't'ort. In this work they were occasionall.\Y 

assisted by Cryptographic Specialists Cyrus C • Sturgis, Jr. , Kenneth 

D. Miller, and Glenn s. La.udig. Of the latter two mentioned, it 

should also be stated that their very large output of' work in the 

decoding of J code material, assisted part time by other members of 

the J-Section, lifted much of' the heavy burden of this absolutel.\Y 

necessary current translation work from the shoulders of the other 

members of the J-Section, thus giving the latter more time for 

research on the B-machine than would have otherwise been possible. 

For the original suggestion of the electrical telephone switching 

mechanism.for duplicating the encipherment of' the n6's", the design 

and construction, in collaboration with Mr. Rowlett, assisted by 

other members of the section, of the machine for deciphering the 

n61 s" and for excellent work in the decipherment of the 1161 s 11 in 

current traffic over many months, Cryptographic Specialist (now 

23 
REF ID:A67329 

1st Lieutenant) Ieo Rosen is to be mentioned. He also supervised 

and assisted in the construction of the hand-operated B-machine 

designed by the crypta.nal.ytic staff of the J-Section; in this latter 

project Junior Cryptanalyst H. F. Bearce, Cryptographic Specialist 

Edward J. Hawkins, Sgts. Wilder and Roy also assisted. In this 

connection, it should also be mentioned that the shop facilities 

of the Radio Laboratory, Navy Ya.rd, were kindly placed at our 

disposal and certain materiel furnished thereat, through the 

courtesy of Commander L. F. Safford of the Communications Security 

Group, Office of Naval Communications. This greatly facilitated 

the construction of the hand-operated B-machine. The excellent 

work of Tabulating Machine Supervisor Ulrich J. Kropf'l and Cryptanalytic Aide Mary J. Dunning in performing countless tabulating 

machine operations deserves mention, as well as the painstaking 

work of the various card punch operators under their supervision. 

Miss Dronenburg performed and assisted in many clerical jobs of 

routine and special. nature in connection with these studies. The 

24 
-- - --· ----·· 

REF ID:A67329 

work of' Research Analysts John B. Hurt and Paul s. Cate must be 

mentioned in connection with our ef'f'orts to reconstruct the texts 

of messages in Japanese. This difficult work had to be done in what 

little time could be spared f'rom their regular and arduous duties 

as translators. The work of' Cryptographic Clerk Frances M. Jerome 

in maintaining the files of' the intercept traffic necessary to these 

studies proved to be extremely helpful; her everyday work in operating 

the 11 61 s" deciphering machine was painstaking and accurate. To 

Cryptographic Clerk Mary Louise Prather credit should be given for 

the careful keeping of the records and index of' all messages; it was 

also she who found the paraphrased K-1 message mentioned in paragraph 

61 and which played an important part in the final. break into the 

system. After the initial solution of' the 11 20'sn had been made 

there was great pressure to hurry the work along as fast as possible. 

In addition to considerable overtime work by members of' the J-Section, 

certain personnel from other sections of the S.I.S. were brought in 

to assist. Some of them performed this work only as voluntary overtime. 

25 
REF ID:A67329 

In this special assistance the names of the following persons are 

to be mentioned: Associate Cryptanalyst Abraham. Sinkov, Assistant 

Cryptanalyst Lawrence Clark, Junior Cryptanalyst Delia Ann Taylor, 

Cryptographic Clerk Wilma z. Berryman, and Cryptographic Specialist 

Edward E. Christopher, Jr. 

The vigilance and excellent work done by our various monitor 

stations in intercepting and copying the necessary traffic also 

deserves special mention. The assistance rendered by G-2 in obtaining 

certain data has already been mentioned. 

The undersigned was directed to participate in the "B" machine 

studies in August 1939, and from that time on these studies were 

under his general supervision, at the same time that he carried 

on some of the duties from which he had not been relieved. In 

addition to this general supervision he also directed and himself 

conducted special studies with a view to uncovering the cryptographic principles un.derzying the B-ma.chine. He wishes to take 

this opportunity to indicate his gratification of the demonstration, 

26 
REF ID:A67329 

by his assistants, of their grasp of the cryptanalytic techniques 

taught them as a result of their participation in the_ training 

afforded by the Signal Intelligence School, as well as his pleasure 

at the manner in which the individual members of the team earnestly 

and "Wholeheartedly collaborated in this joint effort. He also wishes 

to express his appreciation of the important assistance rendered 

by the Officer in Charge of the Signal Intelligence Service, and 

his commissioned assistants, in expediting the procurement of 

personnel, supplies, and special information when needed. 

October 14, 194o William F. Friedman, 

Principal Cryptanalyst