/ 

:· " 

• REF ID:A58137 • 

PRELIMINARY HISTORICAL REPORT 

G N THE 

. S 0 L U T I 0 N 0 F T H E 11B11 

William F. Friedman, 

Principal Cryptanalyst. 

October 14, 1940. 

I 

Declassified and approved for release by NSA on 08-14-2013 pursuantto E .0. 1352a ..... 

~sEeRET 

-SEGREf-
" 

-SECREfli' THE II B11 .ill..CHI~"E 

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 Oka.'1loto, in order that he might put into service certain cr;-ptographic paraphenalia termed by the Japanese diplomatic 

offices as the Type "B" cipher machine. This machine was to replace the 

then currently used Type "A" machine for highly secret com.'llU."'l.ications a.~ong 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 tra.~sposed and 

enciphered by special A-machine procedure) was intercepted and was found 

to give the effective date of the initiation of the B-machine as February 

20, 1939.· The A-machine was still to be used by all holders for certain 

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 "A" type indicator. Examina.tion 

of these messages showed that they v1ere 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. 

'l'he A-machine was continued in regi.ilar use at Hsinking and Shanghai and 

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

the A-machine continued to be eraployed at the places l~1ich had been provided with B-machines. 

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

letters into two categories (one group of six letters and another· 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 11 61 s 11 as well as the 

20 comprising the "20's" 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 1, 2 or 3 steps at a ti.me), in the B-machine the "6's" were enciphered by means of a series of 25 hetergeneous 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 ti.me, and a 

lff SBiRR 

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

Ankara, Shanghai, and Peking. 

SECRET 
-

SECRET 

deciphering chart or "development11 was C·~nstructed to correspond v.i. th these 

25 permutations. This chart was revised and corrected from day to day 

until it· pecame certain that all its elements were absolutely correct. 

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

possible; as a result of cryptanalytic· technique elabcrated for the purpose, 

to decipher the "6's" in practically every message of any considerable 

length in the B-ma.chine. It lvas found that so far as the 11 61 s" between 

two messages with unlike indicators were concerned, the onl~ difference 

bet-A·een cne 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 

r.epresented the same starting point. 

5. 1!lhen the 11 61 s" in a given message were deciph~red, the plain text 

values of cipher Letters scattered here and there throughout the text becanie 

available, so that the skeletons of words and phrases offered themselves 

for completion by the ingenuity and the i.maeination of the cryptanalyst. 

For example, suppose that on a given day the 6 letters forming the 11 61 s 11 

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

Cipher: BR Ax s F/Q c Ev Q 0 1

0 x H b c FD L NH Q av Q pp L c ER p 

Plain: ~HE~A~A_E_E ___ ER __ E __ REQ_E ____ ijA_. 

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

shown below: 

Cipher: 

Plain: 

B R A X E F Q C E V C. 0 0 X H E C F D L N H Q R V t;; P P L C E R P • • • 

IHE~AfANE~EQQYER!hlE!IR£~gE§I&IHAT ••• 

In this process of filling in the plain text values of the 11 201 s 11 the 

cryptanalyst could be guided only by two things: (1) the positions and identities of the deciphered' 11 61 s" 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 statiatical 

and analytical tests made on the cipher texts of the various messages studied. 

6. The process of filling in the plain te:x,t values of the "20's" was 

therefore,as a rule, a very difficult matter, depending usually upon the particular assortment of letters constituting the 11 61 s 11 • If the text was in 

Japanese there was, in addition to the difficulty inherent in that language 

'itself, the added perturbation occasioned by the fact that the Japanese Foreign Office had, on May 1, 19.39, instituted a species of "Phillips Code" in 

connection Vl'i th their use of the B-machine, with a long series of arbitrary 

letters and abbreviations sta.ndine for numbers, punctuation signs, and frequently used combinations of le~ters, syllables, words, and sometimes co~­

plete phrases. For instance, the combination C F C represents period; C C F 

represents paragraph; the single letter L (not normally used in Japanese) . " 
·l· , 

SECRE:l . . 

represents the dir;hthone; ai; X represents ei; P represents ni; V repre- se~~s long U; Q T ~ represents Arita (shi) itashi tashij B KW represents 

Beikoku (• United States); T K \'J represents Teikokuseif'u (• Japanese Government); SN W represents Sukunakarazu, etc., etc. The difficulties introduced by this abbreviated or rather code writing alone vrere quite staggering as well as aggravating, for often the 11 text11 even when finally reconstructed appeared more like code.or a random assortment of letters than 

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

Japanese experts were absolutely essential, and the w'Ork went very slovrly 

not only because of its difficulty, but. also because the services of these 

translators were available only a small part of the time Yihen the traffic 

for the daily "Bulletin" permitted, which was quite seldom. However, occasi.onally it was. found, after the 11 61 s" in a given messa~e had been deciphered, that these letters and their distrj_bution throughout the message 

gave good indications of the presence, in 1.qiole or in part in the message, 

of norm.al English text. In such cases,. the "guessing" process was lik~ly 

to be ccnsiderably easier because of the absence of abbreviations· (except 

for punctuation signs, in ~"hich case these were a help),because of the 

2 A typical example of the sort of 11 text11 usually found at the beginning of 

messages is the following: 

Cipher: F G P X P I X U D B D G E C Z L B L N U 

Plain: X F C G J W F 0 V n· D N 0 B B F Y X F 0 

ZQO~H YNMRQ ARJOP 

C F Y L C C F ~ S G T S J VR 

DEILO AXPPP LIGDK ZFGRA 

KHIFI CGURV FELBK WTLSI 

The correct grouping of letters and the interpretation of the foregoing 

"plain text" is as follows: 

x F c = Dai - go 

G J W = 15 

F 0 V = Open parenthesis 

DD = 2 

N 0 = "cf" (Jap.plain text 

particle possessive) 

BB = 1 

F Y X = Close parenthesis) 

F O C = Gokuhi (= Secret) 

F Y L = Kancho fugo atukai 

C C F = Shin sho ( = Paragraph) 

Ais = 3 G T S : Getsu (month) 

J V R K = JUroku (= 16th) 

H I = Japanese word for "da:'.r" 

F I C = Begin kana spelling 

G U R V = Gurii (= Grew) 

F E L = Close kana spelling 

B K 1.'! = Beikoku ( = U. S • ) 

T L S I = Taishi (= .Ambassador) 

In running language, the message begins as follows: "Number 15 (part 1 of 

2 parts) ~e·cret, to be kept ·;d thin the Department paragraph On March 16th 

the American Ambassador, Grew", etc. 

- 3 SECRCT 
cr~'ptanalyst' s :zrea ter fe..m.iliari ty .. ii. th the lane;uae;e, and because of the 

availability of the services of a larger number of ~orkers. It happened 

that in several cases, after a few ~~rds had thus been obtained by pure 

11 guessing", a clue v:as afforded as to the 3ener[~.1 nature of the messa:;e 

SiCRr. l 

and this led to a frantic search for a complete document which might be 

available either in our ovm files or in the files of other government 

agencies. One case was found in which the B-machine message contained a 

paraphrased version of a messaee which had been transmitted in K-1 code. 

Ad.v&ntage was, of course, i.Ir.mediat.ely taken of tbis circumstance but the 

entire text of the B-machine messaee could never be reccnstructed from the 

paraphrased K-1 versjon, possibly because of the excellent paraphrasing, ~ossibly because of the presence.of abbreviations, possibly because of both. 

Certain ~nglj_sh text messa2es, hov1ever, were reconstructed, some of them to 

the extent of 90-95%, because the doct:ments being quoted in the messaees 

-nere fortunately located and obtained, most often through the cooperation 

and good offices· of G-2. • 

?. In all, the ~lain texts for parts of some 15 fairly lengthy 

messages were obtained by the methods indicated above, and these were subjected to most intensive and e>:haustive cryptanalytic studies. To the 

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

a coinplete and absolute absence of any causal repetitions· within any sinc;le me~.sage, no matter how long, or between two messages with different indicators on the same day, but also that when repetitions of three, or occBsionally four,ci~her letters ~found, these never represented the sa..~e 

plain text. In fact, a statidtical calculation 2avc the astonishing result 

_that the number of repetitions actually present in these cr;,rptogra.."ils was 

:..;;is ti:1an the number to be expected had the letters comprising them been 

-·~··:n at rarldo:::n out of a hatt_ Apparently, the mctchine had with malicious ~.:1: ent -- but brilliantly -- been constructed to suppress alJ.: plain text 

repetition. Nevertheless, the cryptanalysts h.sd a feeling: that this very 

circumstance nould, in ~e final analysis, prove to be the 11 uncloingn of the 

system and mec!ianism. .And so it turned outl 

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

the basic law underlying tbe 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, 

strai:;ht throu2;h to the end of the messages, the longest of which for which 

plain text had been recovered comprised over 1,500 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 identicaJly. enciphered. This phenomenmwM.ch was 

termed "suppression of duplicate encipherments at the 1st and 26th intervals" formed the subject of long and arduous stuJy, fruitless experimentation and much discussion. Thirdly, two messages vrith identical indicators 

0n the saine day appeared to be identically enciphered, and on direct superimposition shovred themselves to be monoalphabetic within columns, 

but v'ii. th the monoalphabets constantly, ir·regularly and unpredictably shifting from column to column. Fourthly, two messages with identical indicators 

. . ' "~I je'")'j' 

l~ I I I ! i' _, 
~J LL~ L~ qi\~ .' I _..,LJi \,ll-':::1! i 

on different days (different plugboard arrangements into the :nachine) were 

absolutely different. Fifthly, two messaees ..,.ri th different indicators on 

the same day (same plugboard arrangement) were absolutely different and 

shoYied no cr.~';itogra1)hic 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 cculd, and often did, occur ·within a line of 26 letters at all intervals, except at the 1st interval, 

althour:;h this pher.omenon was rare at the 2d, Jd, 4th and 5th intervals. 

9. At the same time as the foregoing phenomena wer'e being studied, 

intensive research Kas.ccntinued in ·an endeavor tc establish primary or basic 

cipher sequences of ·the nature of those usually found in cryptographs with 

rotating cO.iJnutators, rotors, and the like, such as in the Hebern and Enigma 

cryptographs, our hl-134, etc.· For it .-.ras inccncei vable that the macM_ne employed a multiplicity of non-repeating keys of lengths corresponding to the 

lengths of the messat;es and, moreover, theoretical considerations eliminated 

the possibility that run..'1ing keys were being used. Somewhere, somehow, the 

existence of cyclically repeating keys or sequences must he uncovered before 

solution could 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 sec;.uences as were being 

sought. In a certain English text message the letter E was found to be 

represented by Q, 26 letters ay.,ay another E •vas found to be represented by 

Y, and aga:i.n 26 letters away another E was found to be represented by V, 

:nakine; the sequence QYV; in the very same message the same trieraph Q Y V 

was found to represent three I:'s simi..larly spaced. Attempts to add to this 

'Q Y V sequence were absolutely unavailin~:. In this long, exhaustive and 

tedious search for repeated sequences or partially repeated sequences much 

labor and energy y;a.s expended but it was realized that the difficnlt~,r was 

probably due to the paucity of the text, despite the number and length·cif 

the individual messages c:.vailable for stu<ly nnd for which the plain text 

had been reconstructed. It b~~@.._§..marent .J.h~~-!'.{hat ·.~rould _Q.§..ll~C-~~~Cl~ ..!:@§ 

I-o obtain, . .Ex-some mann~~r.:._Q!:._O ther:,_~"!!":d:~l •ll.~~~~~J~Il- th.~.....§!1~.iil.dJcatQ..~ 

~l'..!~ _on the same dav, or else ~9_cc~eri.__~~-~~:i;'_?.l mess.'.l.rre_s :·;i tf! t~~ ..:W.!!E!. indicator bu~_on differe..11!: .. day~-~Q.-~h.~-~C!i.!!~.J~.~§.e i. 2.~~or~ ___ q_'!_~ th~istence __ qJ: 

such cyg_J.:_~~O.J!.~11£~~~11.J~EL..£~ ec _te?.,!.. 

10. In all the thousa.i."ld or 11ore messar;es on hand there were but a 

mere baker's half dozen or so cases ••here there were two ,nessa3es on the same 

day ;md in the sazne indica. tcr. ::lore than two had never been found a.nd this 

was to be expect~d in a system with 120 different indicators available for 

selection each day. In one case o.f tr.is ra.re phenomenon the plain text for 

one of th.a two m'3ssages v;as ·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 sane indicator 

a'.-.d on the sai11e day would be necessary and this was of course recoenized as 

a perfectly hopeless expectation. There re:na"!.ned the possibility of converting several messages with the sa:.""ae indicator but on d.i:'f-arent days to 

the sa:.ne base and 1"Thile this met:1od of attack looked extremely difficult 

it did not appear hooeless.._ ... -.... .-• 

~ 

~ 

- 5 -
11. A method for this conversion to the same 1'a,se Vias (lev~loped 

and was ter31ed "the identification of homologs." That ii:i, an attempt was 

to be made to establish that a given letV:!r on a certain day and another 

letter on a differe?'.J.t day '':ere treated in an ·absolutely identical or, .nore 

accura t.ely speaking, ho11ologou~ manner by the machine when .s<:: t to the sai,1e 

indicator. Tliis convers"Lon process is too involved to explain in this re.:.. 

port but suffice it to say that difficult thout;h it is, it was successfi.11 

in two cases. One of these ~rielded a set of 6 .~essages, ,all in indicator 

59173, which could all ~e reduced to the sc;.rne base. .'J.'hese f crmed the cru-. 

cial set of messages from the study of vrhi.ch success in solution of the 11Uichine \l'Tas fina.lly achieved. 

12. Distribution tables of the letters constitutine the text of · 

these six messages were made. It should be stated that in f::mr of ti1ese 

.... six crucial messages only fraements of plain text had been reconstructed, 

here and there; the coinplete o~ nearly compl~te plain texts of only two of 

these six messages had been reconstructed. Hm·mver, enoueh data •·:ere accurnulated from these t·::o co:npletely and the other partially reconstructed messages to yield distribut:i.on tables vrhich, on careful examination, disclosed 

the presence of repeated sequences, ·here and there. This, on 3eptem::ier 2:), 

1940, at about 2:00 P.TU., was the v3ry first indicHtion that a successful 

attack :night be possible. There was :nuch excitement at this first ;:rlimmer 

of licht upon a subject that had for so r:mny months been shrouded in cor:J.?lete 

darkness and regarued occasionally v:i th sorne d.iscourac;e:nent. The nature of 

the distribution tables rel:erred to is also too involved to ezplain in this 

report, but suffice it to indicate that they showed certain symmetries betw~en the successive cipher equivalents of a given plaLn-text letter and the 

successive appearances of that pla;n-text letter in the cr:-,rptogra::,·inic text. 

13. As soon as the existence of cyclic or symmetric sequences became clear, attempts were made to uncover complete ba.sic sequences of the 

t;ype theoretically predicted. But many conflicts and inco!"lsistencies soon 

developed, due to the fact that the cr~c.togra.i:.hic laws underlying the shifting from sequence to sequence \'rere still unknovm. Concurrently V'ri th the 

work connected -..Ti th straightaning ·out and removing inconsistencies in these 

reconstructed basic sequences ran the v10rk of uncover·j_n~ the cryptographic 

laws referred to, and very soon the genera~ nature of the latter beca~e 

quite clear. All efforts were concentrated upon the development of the 

specific laws and specific basic sequences a.;!plicable to the indicator 

under study, viz, 59173, with a view to uncovering all the cryptographic 

phenomena in this case and. then 'searching for analogous phenor.iena in the 

case of other indicators. Certain qualified personnel .from other sections 

v:ere brought in to assist, a.."1d a consid.erable amount of night work vras · 

found desirable in order to push this study to completion at the earliest 

possible :noment. 

14. :ay September 27, just one week later, the ViOrk had progressed 

to a point where it bec&i1e possi<:ile to hand in t•~o translations repreGenting the very first "solutioll11 to the 3-.m~ch:i.ne. Two .:nessages of recent 

dates, both in the 59173 indicator, were avaj_lable and vrere solved by 

,, 

I' 

0 - SEG'.iET 
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 annou..'lcer,1ent viras ;n.ade of the signing of 

the Tripo.rti te Agreement a-:i.ong Germany, Italy, and Japan. 

SECREf15. Much i'irork re:nained to be done, ho-.•,ever, since only the datR. 

applicable to but one out o!' the w!10le set of 120 indicators were at hand. 

Tc solve the remaining 119 indiGators appeared still to present quite a 

large problem. These solutions ccnsist of findine; the initial settings of 

three 20-level rotary, electr~cal cryptcgra~:l:ic elements of 25 points each, 

and finding the crd.:3r in v;hich these three elements are brought i:ito play 

within each indicator sys tam. ~·;1th but little slackening of the pace set 

by th.a personnel the.11selves, work has progressed with vigor and at this 

moment soluti0ns for over one-third of the 120 indicators are available. 

16. As to the 1n~chanics 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 o.f an equivalent machine for our purposes. Orders for 

the materiel for 2 fully automatic machines were placed and ex!Jedited. \'ibile 

awaiting the arrival of this materiel a hand-operated machine vims desi•gned 

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-iaacl:"ii.ne 

consists of 13 rotary, 6-level, 25-point, switches of the type employed in 

automatic telephon;;r. One of these 13 switches controls the encipherment of 

the 11 61 s 11 and it goes through the same 25-point cycle over and over again as 

many tL~es as is necessary to encipher the messages. It has 150' crossconnectl.ons, \vhich, 8S stated above, had been established long ago. As to 

the 11 20' s 11 , these are enciphered by means of 3 banks of 4 s~vitches each, each 

bank having 500 cross-connections, makine a total of 1,500 sub-circuits available for the encipherment of any given letter. The arran~ements for advanc-· 

ing these svli tches is such that for a given indicator, say 20346, bank number 3 steps ccntinuqusly, bank number 2 steps once for every 25 steps of bank 

number 3, and bank number 1 steps once for ev;;ry 625 steps of bank number 3. 

This type of motion has been desien~ ted as a 11 32111 motion. For a..'lother 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-J, 2-3-1, 3-1-2, and 

3-2-1. Althoueh there .are 120 different indicators there ar~ only 6 different 

types of motion or step,t)ing of the three ciphering switches, so that it appears that each type of motion is representf!d by 20 different indicators. 

Vfr1at differentiates one indicator from another within such a set of 20 indicators are the relative starting points within the three banks of s·witches. 

These starting points appear to have been very carefully selected so as to 

preclude or reduce the possibility of 11 overlaps," that is, the production of 

two messages wr!ich in whole or in p.art have been enciphered by identical keying ele.~ents in identical sequence. Once these factors concerning all indi~ators have been established, and our machine is in operatLon, the reading 

of B-:nachine messages resolves itself into the establishment of the dailv 

plugboard arrangement, that is, the order and identity of the wireo leading 

from the keyboard into the cryptograph and thence out of the cryptograph 

into the printing unit. Cryptanalytic procedures for thi:::: purpose have al- " 

ready been established and tested so that this should not be a serious - - ~=;) 11 "i)i 11::-'\ r ·P ', ,) ! ~ r=t~ • , IJ ~ l.! • , I.I · 1 .Q. 
! ' 

.. 

SECRET 

problem. Given a long message or several short ones of the same date, 

solution should be possible in an expeditious manner. 

1'7. The solution of the B-machine has, as a concomitant, thrown 

considerable lj_ght upon the mechanism of the A-mach:l.ne ir.'i th the result 

that our present A-machj_ne will be modified in the light of these disco:veries and V'd.11 be made more efficient. The whole situation ·with respect to 

the cipher machines em.:.loyed by the Japanese Foreign Office now appears 

to be interrrated into a consistent scheme of development from its earliest and ~implest beginnings, about 1930, to its present quite complex 

fcrm. Problems concerning the l\-machine and questions for which logical 

and 11 reasona.bleu ans\1rers could not be four1d are now explainable on the 

sim}lle grounds or" the typ~ of cryptoerE.phic mechanism employed in the 

earlier machines, which seems to be the rotary switch used in automatic 

telephony, rather than the revolving commutator employed in our present 

A-macM.ne. 

Part. II. Credits 

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

of 18 months of ~-ntensive study by a group of cryptanalysts and assistants 

working as a harmonious, well-coordinated and cooper.:.tive team. Only by 

such cooperat:i.on 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 t.ea."Tl. may, however, be 

ind.icated. 

19. The specific direction and coordination ·of all studies on this 

project was the joint work of Cr;y-ptanalyst Fra..."lk B.Rowlett and Assistant 

Cr!:ptar,alyst D.obert O. }""'err.er. Their indefatigable J:aOors and brilliant 

analytical work testify and are a credit to thei.r cryptanalytic skill, training ano ex?erience. To their joint uirection and effcrts are due the extremely fruitful analysis of the cryptographic mechanics underlying the 

operation of the B-machine as r.t whole, the theory of its opere.tion, and 

tne developm:mt anC. solution of the 11 61 s 11 at any early date in these studies •. They were also extremely active in pushing the solution to a successful ccnclusion by orga.nizinc; a.11d d.irectinc the reconstruction of the 

developments or wirings of the switches for tne 11 20 1 s 11 • Junior Cryptanalysts Gcr.evieve ;;;,. Grotjan, Albert·.:. Small, and. ::3amuel S. Snyder did 

:uost excellent work in recovering the 11 61 s" during many months of apparently hopeless effort. In this work they were occasionally assistGd by 

Cryptogra:t:ibic Specialists Cyrus C. Stureis, Jr., Kenneth D. ~...:ill er, and 

Glenn S. Laudig. Of the la.tter two mentioned, it should also be stated 

that their very large output of 1'lork in the decoding of J code material, 

assisted part ti.11e by other inembers of the J-Section, lifted much of the 

heavy burden of •tr_is absolutely necessary current translation work from the 

- 8 - -SECREf 
~· 11 . . c.-' 7" . --- ' :~~ .......... u~ '\ .. • 

shoulders of the other members cf the J-section, thus giving the latter 

more ti.il.e for research on the B-machine than would have otherv:ise been 

possible. For the original suggestion of the electrical telephone S!"d.tching mechanism for duplicating the encifJhernent of the 11 61 s!', the d~sign 

and construction, in collaboration iTi th ~;:r. ftowlett, assisted by other 

me:nbers of the sect:;.cn, of the !lachine for deciph•3ring the 11 6 1 s:' and for 

excellent wor~ in the deciphzr:nent of the 11 61 sn in current traffic over 

many mcnt~s, CrJrptographic Specialist (no"'.'i' 1st Lieutenant) Leo aosen is to 

be mentioned. He also supervised and assisted in the construction of 

the hand-operated E-machine designed b;{ the cryptanalytic staff of the 

J-section; in this latter _:Jrojsct Junior C:r:'Ptanalyst H. F. ::3earce, Cryptogra.!,)hic Specialist E.dwarc.l J. !!aw::dns, Sets. -.. -.!..lder end J.oy also assisted. 

In ti·,is connection, it should also be :aent:!.onec'!. that the shop f.::.cilities 

of the I:.adio Laboratory, :t~avy Yard, ,,.~ere kindly pl.s.ced at our C:isposal and 

certain .:nateriel furnished thereat, through the courtesy of Commander L.F. 

Safford of the Co:mnunications Security Group, Office of Kaval Communications. This ,::reatly facilitated the construction of the hand-operated 

B-machine. The excellent work of ·Tabulating :Uiachine Supervisor Ulrich J. 

Krapfl end Cryptanalytic f\ide i.:ary J. Dunning in p:::rfcnning countless tabulating ma.chine operaticns deserves mention, as well as the painst.a.king 

~ork of the various card punch operators under their supervision. hliss 

uronenburg perfcnned and assisted in many clerical jobs of routine and 

special nature in connection with these st'\;..dies. The work of Resea.rch 

Analysts John .a. Hurt and Paul S. Cate must be mentioned in connection 

·with our efforts to reconstruct the texts of messaees in Jarc·ei.nese. This 

di.f"ficul t \'I Ork had to be done in ;;hat little time could be spared from 

their regular and arduous duties as translators. The work of Cr~rptographic 

Clerk F'rances ~. Jerome in maintaining the fj les of the intercept traffic 

necessary to these studies proved. to be extremely helpful; her everytlay work 

in operating the 11 61 s 11 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 messaE;es; it was also she who 

found the para.r1hrased K-1 message mentioned in Par. 6, and wrd.ch plc:.yed an 

important part in the final bre<ik into the system. After the initial solution of the 11 20 1 s" had been' made there was great pressure to hurrv the v;ork 

alone as fast as possible.~ In addition to considerable overtime ;rork by 

members of the J-section; / certa.in personnel from other sections of the 

~.I.S. "1.rere brought in to assist. Some of them performed this vrork only 

c:s voluntary overtime. In this special assistance the na."!les of the following persons are to be mentioned: J._ssociate CryptaTlalyst Abraham Sinkov, 

Assistant Cryptanalyst Lawrence Clark, Junior Cryptanalyst Delia Ann Taylor, 

Cryptographic Clerk 11ilma z. Berryman, ancl·Cryptoeraphic Specialist Edward 

E. Christopher, .Jr. 

The vigilance and excellent work done by our various monitor sta.-

tions in intercepting and copying the necessary traffic also deserves 

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

bas 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 :bis 

;;eneral supervision, at the sa'!le time that he carried on some of the duties 

fro-::i. which he had riot been relieved. In addition to this general supervision 

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he also directed and himself conducted special studies T.i th a view to uncovering the cryJ,:togra.:.Jhic principles underlying the B-mscr.ine. He rd.shes 

to take t:·:is opportunity to indicate 11is-·zratification of the demonstration, 

by his assistants, of their i:;rasp of the cr::pta.11alytic techniC1ues taught 

them as a res1!lt of their participation in the trainine afforded by the 

Signal Intelligence School, as well as bis pleasure a.t the manner in v;hich 

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 Charee of the Signal Intelligence Service, and his commissioned assistants, in expediting the procurement of personnel, supplies, and special information when needed. 

October lL,., 1940 

- 10 -

~~:illia.m F. Friedr.1a.n, 

Principal Cryptanalyst. 

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