colossus its origins and originators-

Colossus, the large-scale special-purpose elec-tronic computer used for code breaking in the19391945 war with Germany, completed itsfirst trial runs in December 1943 (two yearsbefore the first comparable US computer, theENIAC, was operational).1 From February 1944,cryptanalysts used Colossus to read the price-less German traffic code-named Tunny bythe British. The exact timing of the D-Day land-ings in June 1944 was based on intelligenceproduced by Colossus.

Traditional histories point to Alan Turing asthe key figure in the design of Colossus. Yet therecently declassified official history of theattack on Tunny states: Colossus was entirelythe idea of Mr. Flowers.2

Biographical backgroundThomas H. Flowers (19051998) joined the

Telephone Branch of the Post Office in 1926,after an apprenticeship at the Royal Arsenal inWoolwich (well-known for its precision engi-neering). Flowers entered the Research Branchof the Post Office at Dollis Hill in NorthLondon in 1930, achieving rapid promotionand establishing his reputation as a brilliantand innovative engineer. At Dollis Hill, Flowerspioneered the use of electronics on a largescale. In 1934, he employed 3,000 to 4,000valves (vacuum tubes) in an experimentalinstallation for controlling connectionsbetween telephone exchanges by means ofvoice-frequency tones (1,000 telephone lineswere controlled, each line having three to fourvalves attached to its end). Flowers design wasaccepted by the Post Office, and the equipmentwent into limited operation in 1939. During19381939, Flowers worked on an experimen-tal, electronic high-speed digital data store foruse in telephone exchanges. Flowers was firstsummoned to Bletchley Park to assist Turing inthe attack on Enigma but he soon became

involved in work on Tunny. After the war,Flowers pursued his dream of an all-electronictelephone exchange and was closely involvedwith the groundbreaking Highgate Woodexchange in London, which was the first all-electronic exchange in Europe.

Max H.A. Newman (18971984) was a lead-ing topologist as well as a pioneer of electronicdigital computing. A Fellow of St. JohnsCollege, Cambridge, from 1923, Newman lec-tured Turing on mathematical logic in 1935,launching Turing on the research that led tothe universal Turing machine.3

Newman assisted Turing with the final draft-ing of the latters 1936 paper On ComputableNumbers, with an Application to theEntscheidungsproblem.4 At the end of August1942, Newman left Cambridge for BletchleyPark, joining the Research Section and enteringthe fight against Tunny. In 1943, Newmanbecame head of a new section known simply asthe Newmanry, home first to the experimentalHeath Robinson machine and subsequently toColossus. By April 1945, there were 10 Colossiworking round the clock in the Newmanry. InSeptember 1945, Newman took up the FieldenChair of Mathematics at the University ofManchester and, inspired both by Colossus andby the abstract universal stored-program com-puter described in Turings On ComputableNumbers, lost no time in establishing a facili-ty to build an electronic stored-program com-puter. Newman was soon joined by theengineers Freddie Williams and Tom Kilburn,and on 21 June 1948, in Newmans ComputingMachine Laboratory, the worlds first electron-ic stored-program digital computer, theManchester Baby, ran its first program.

Alan M. Turing (19121954) was in 1935elected a Fellow of Kings College, Cambridge,at the age of only 22.5 On ComputableNumbers, published the following year, was

Colossus: Its Origins and Originators

B. Jack CopelandUniversity of Canterbury

The British Colossus computer was one of the most important tools inthe wartime effort to break German codes. Based on interviews andon recently declassified documents, this article clarifies the rolesplayed by Thomas Flowers, Alan Turing, William Tutte, and MaxNewman in the events leading to the installation of the first Colossusat Bletchley Park, Britains wartime code-breaking establishment, inDecember 1943.

38 IEEE Annals of the History of Computing Published by the IEEE Computer Society 1058-6180/04/$20.00 2004 IEEE

Authorized licensed use limited to: KINGS COLLEGE LONDON. Downloaded on November 30, 2009 at 10:28 from IEEE Xplore. Restrictions apply.

his most important theoretical work. It is oftensaid that all modern computers are Turingmachines in hardware. In a single article,Turing ushered in both the modern computerand the mathematical study of the uncom-putable. During the early stages of World WarII, Turing broke German Naval Enigma andproduced the logical design of the Bombe, anelectromechanical code-breaking machine.Hundreds of Bombes formed the basis ofBletchley Parks factory-style attack on Enigma.In 1945, inspired by his knowledge of Colossus,Turing designed an electronic stored-programdigital computer, the Automatic ComputingEngine (ACE). Turings design became the basisfor the very successful Digital ElectronicUniversal Computing Engine (DEUCE) com-puters, which were a cornerstone of the fledg-ling British computer industry and remained inuse until about 1970.6 At Bletchley Park, andsubsequently, Turing pioneered artificial intel-ligence. He also pioneered the discipline nowknown as artificial life, using the Ferranti MarkI computer at Manchester University.

William T. Tutte (19172002) specialized inchemistry in his undergraduate work at TrinityCollege, Cambridge, but was soon attracted tomathematics. He was recruited to Bletchley Parkearly in 1941, joining the Research Section.Tutte worked first on the Hagelin ciphermachine and in October 1941 was introducedto Tunny. Tuttes work on Tunny, which includ-ed deducing the Tunny machines structure, canbe likened in importance to Turings earlierwork on Enigma. At the end of the war, Tuttewas elected to a Fellowship in mathematics atTrinity; he went on to found the area of mathe-matics now called graph theory.

The Tunny machineTunny, quite distinct from Enigma, was a

system of teleprinter (the North American termis teletypewriter) encryption. (Colossus is some-times incorrectly stated to have been usedagainst Enigma.) Technologically more sophis-ticated than Enigma, Tunny carried the high-est grade of intelligence. From 1941 onward,Hitler and the German High Command reliedon Tunny to protect their communicationswith Army Group commanders across Europe.7

Tunny messages sent by radio were first inter-cepted by the British in June 1941. After a year-long struggle with the new cipher, BletchleyPark had its first successes against Tunny in1942. Tunny decrypts contained intelligencethat changed the course of the war in Europe,saving an incalculable number of lives.

To clarify the contributions made by

Flowers, Newman, Turing, and Tutte to theattack on Tunny, it is necessary to outline theworkings of the Tunny cipher machine.8 TheTunny machine (which measured 19 15-1/2 17 high) was a cipher attachment, automati-cally encrypting the outgoing stream of pulsesgenerated by the teleprinter to which it wasattached, or automatically decrypting incom-ing messages before they were printed. At thesending end, the operator typed plaintext atthe teleprinter keyboard, and at the receivingend the plaintext was printed out automatical-ly by another teleprinter (usually onto paperstrip, resembling a telegram). The transmittedciphertext was never seen by the German oper-ators. In batch mode, many long messagescould be sent one after another: The plaintextwas fed into the teleprinter equipment on pre-punched paper tape and was encrypted andbroadcast at high speed.

Enigma was clumsy by comparison. Thecipher clerk typed the plaintext at the keyboardof an Enigma machine while an assistantpainstakingly noted down the letters of theciphertext as they appeared one by one at themachines lamp-board. Once the ciphertext wascomplete, it was passed to a radio operator fortransmission in Morse code. In Tunny, Morsewas not used: The Tunny machines outputencrypted teleprinter codewent directly to air.

International teleprinter code assigns a pat-tern of five pulses and pauses to each character;using the Bletchley convention of representinga pulse by a cross and no pulse by a dot, the let-ter L, for example, is xx, M is xxx, N isxx (in modern notation: 01001, 00111, and00110, respectively). The plaintext enteredTunny in the form of teleprinter code and wasencrypted by means of the bitwise addition of afurther stream of dots and crosses, generatedautomatically by the Tunny and known as key.Dot-and-cross addition is Boolean XOR: Dotplus dot is dot, cross plus cross is dot, dot pluscross is cross, cross plus dot is cross. For exam-ple, if the plaintext message is simply JA, andthe key for this message is MT, then the cipher-text is QW. J + M = Q and A + T = W:

J A

xxx xx Q W

+ + = xxxx xxxxxx x

M T

The obscuring key was generated by theinternal wheels of the Tunny machine. Eachtime a letter entered the encryption mecha-nism, some (or all) of the wheels would moveforward one step. The wheels had adjustable

OctoberDecember 2004 39


metal cams around the circumference. Eachtime a wheel moved forward a step, a differentcam reached a stationary switch, producingeither a cross (that is, a pulse) or a dot. A camin the so-called operative condition produceda cross, and in the inoperative condition, wherethe operator had moved the cam to one side, adot.

Each wheel (there were 12) had a differentnumber of cams, varying from 23 to 61. Thearrangement of the cams, operative or inoper-ative, was identical in the sending and receiv-ing Tunny. The Germans left the arrangementunchanged over many messages.

Two groups of five wheels produced the key.Each wheel in a group contributed one bit, dotor cross; the group as a whole contributed a sin-gle character. The character contributed by onegroup was added to the character contributedby the other to produce one character of key.For example, if one group contributes xxx(U) and the second xxxx (Q), the character ofkey is x (T): U + Q = T. The two groups ofwheels were known at Bletchley as the -wheelsand the -wheels, respectively. (The remainingtwo wheels, the motor or -wheels, served tocreate irregularities in the movement of the -wheels. The -wheels, on the other hand,moved regularly, rotating every time a letterentered the Tunny.)

Decryption relied on the fact that addingany characters x and y and then adding xagain a second time retrieves y: (x + y) + x = y.The receiving Tunny generated the same char-acters of key as the sending Tunny and addedthem to the ciphertext in order to reveal theplaintext.

As with Enigma, the sending and receivingoperators would rotate the wheels of theirmachines to the same numbered positionsbefore the encryption (and decryption) of amessage began, thus causing the same key to beproduced. From October 1942, the 12 numbersspecifying the positions were obtained from abook that was issued to the operators at eachend of the Tunny link. Each book listed 100 ormore different sequences of 12 numbers; aftereach sequence had been used once, the bookwas discarded, and the operators moved on tothe next.

The structure of the Tunny machine wasdeduced in January 1942 by Tutte, with someassistance from other members of BletchleyParks Research Section, on the basis of a pair ofintercepted messagesa remarkable feat, to saythe least. It was not until the very end of thewar that the code breakers saw a capturedTunny machine.

Misconceptions about the history ofColossus

Martin Davis offers the following account ofthe British attack on Tunny:

Some of the methods used were playfully

called turingismus indicating their source. But

turingismus required the processing of lots of

data and for the decryption be [sic] of any use,

the processing had to be done very quickly In

March 1943, Alan Turing sailed home from a

visit of several months in the United States He

whiled away the time during his Atlantic passage

by studying [an] RCA catalog, for it had been

found that vacuum tubes could carry out the

kind of logical switching previously done by elec-

tric relays. And the tubes were fast Vacuum

tube circuits had in fact been used experimental-

ly for telephone switching, and Turing had made

contact with the gifted engineer, T. Flowers, who

had spearheaded this research. Under the direc-

tion of Flowers and Newman, a machine, essen-

tially a physical embodiment of turingismus, was

rapidly brought into being. Dubbed the Colossus

and an engineering marvel, this machine con-

tained 1500 vacuum tubes.9

This account of matters is garbled. Otherprominent accounts are also in error; for exam-ple, J.A.N. Lee, in a biographical article onTuring, says that his [Turings] influence onthe development of Colossus is well known,and in an article on Flowers, Lee refers toColossus as the cryptanalytical machinedesigned by Alan Turing and others.10 Leestates:

Newman fully appreciated the significance of

Turings ideas for the design of high-speed elec-

tronic machines for searching for wheel patterns

and placings on the highest-grade German enci-

phering machines, and the result was the inven-

tion of the Colossus.11

Even a book sold at the Bletchley ParkMuseum states that at Bletchley Park Turingworked on what we now know was comput-er research which led to the worlds first elec-tronic, programmable computer, Colossus.12

Turingery and TutteryIn July 1942, Turingon loan, for a period

of a few weeks, from the Naval Enigma sectionto the group researching Tunnydevised amethod of attack officially named Turingery.13,14

An unofficial slang term for this method,Turingismus, was coined subsequently. (LeadingTunny-breaker Donald Michie recalled:

40 IEEE Annals of the History of Computing



[T]hree of us (Peter Ericsson, Peter Hilton and I)

coined and used in playful style various fake-

German slang terms for everything under the

sun, including occasionally something encoun-

tered in the working environment. Turingismus

was a case of the latter. (Personal communica-

tion, July 2001.))

I will use the official term Turingery in pref-erence to the slang term for the method.Turingery was a hand method, involving paper,pencil, and eraser. Its function was wheel break-ing, starting from a stretch of key.15,16 Wheelbreaking is the finding of the arrangement ofthe camsoperative or inoperativearoundthe wheels. Once gained by Turingery, thisinformation remained current over the courseof many messages. (At first the Germanschanged the cam patterns of the -wheels oncea month and of the -wheels quarterly; fromOctober 1942, the -wheel patterns were alsochanged monthly. From August 1944, all wheelpatterns were changed daily; although by thattime new methods of wheel breaking were usedin preference to Turingery.)

Turingery was used in conjunction withdepthstwo or more messages enciphered atthe same starting positions of the wheels, anegregious breach of secure cipher practice. Itwas from depths that the stretch of key neces-sary for the application of Turingery wasobtained (also by hand). Turingery extractedfrom the key the contribution of the -wheels.From this, the cam patterns of the individual -wheels could be deduced; further deductionsled to the cam patterns of the - and motorwheels.

Given successful wheel breaking fromdepths, the next hurdle was to find the startingpositions of the wheels for each individualTunny message (not just the few messages thatwere in depth). This process was known aswheel setting. After setting, the messages couldbe read. Tutte invented a procedure for wheelsetting in November 194213 that becameknown as the Statistical Method.

Both Turingery and the Statistical Methodused a process of sideways bitwise additionknown as differencing. Differencing xx, forexample, produces xxx (dot plus cross, crossplus dot, dot plus dot, and so on). Differencingtracks changes in the original stream of dot andcross. If a dot follows a dot or a cross follows across, then the corresponding point in the dif-ferenced stream has a dot; if cross follows dotor dot follows cross, then the differencedstream has a cross. A dot in the differencedstream means no change, and a cross means

change. Turing introduced differencing in July1942: He made the fundamental observationthat differenced key could yield informationunobtainable from ordinary key.17 Turingeryworked on the differenced key to produce thedifferenced contribution of the -wheels. Tuttediscovered, a few months later, that differenc-ing was the clue to wheel setting.

Tuttes Statistical Method is as follows.14 Letattention be focused on the first two -wheels,1 and 2. As each rotates through all its possi-ble positions, it produces a stream of dot andcross whichassuming that the wheels havebeen brokenis known to the cryptanalyst. Ifthe two streams are added and their sum dif-ferenced, the result is a periodic sequence; theperiod is 41 31 = 1,271, since there are 41cams around 1 and 31 around 2. One of these1,271 places in the sequence represents theposition of the two wheels at the start of enci-phering the message. The problem is to find it.The first step is to prepare the interceptedciphertext in a certain way. At Bletchley, eachof the five streams of dot and cross making upthe ciphertext was called an impulse. For exam-ple, if the ciphertext is QW, as in the previousexample, the first and second impulses are bothxx, the third x, and so on:

Q Wx xx xx x x

The first and second impulses of the cipher-text (written c1 and c2) are added and the resultdifferenced. (A message of about 1,000 charac-ters or more is required.) The differenced c1 + c2is then laid against the differenced 1 + 2 ineach of the possible 1,271 positions, and ateach position the number of times that the twostreams agreethat is, have a dot or a cross inthe same placeis counted. The position withthe highest score is, Tutte showed, likely to bethe start position of the two wheels.

Further applications of Tuttes methodreveal the start positions of other -wheels. Thestart positions of the - and -wheels can thenbe found by less computationally intensivemethods.

The small statistical bulge at the correct startposition, on which Tuttes method depends, isthe result of the pattern of movement of the -wheelsthe great weakness of the Tunnymachine. Each time a letter entered the encryp-tion mechanism, the -wheels would either all



step forward (like the chis) or all remain still,depending on the position of the motor wheels.(The motion of the psis was described as stagger-ing at Bletchley Park.) While the psis remainedstationary, they continued to contribute thesame letter to the key. So, since differencingtracks change, the differenced -stream con-tained more dots than crosses. The effect wasboosted by the fact that the differenced plaintextalso contained more dots than crosses, thanksboth to the statistical properties of the Germanlanguage and the practices of Tunny operators,who habitually repeated certain characters. Theresult was that at the correct start position, thedifferenced 1 + 2 would agree with the differ-enced c1 + c2 more often than not.18 When thetwo were correctly aligned, counting the num-ber of times that they had a dot or cross in thesame place usually produced a result that washigher than chancenot much higher, but anyregularity is the cryptanalysts friend. If, insteadof the -wheels either all moving together or allstanding still, the designer had arranged forthem to move independently (or even to moveregularly like the chis), then the chink that letTutte in would not have existed.

Turings method of wheel breaking fromdepths and Tuttes method of wheel settingwere distant relatives, in that both used differ-encing. But there the similarity ended.(Turingery, Tutte said, seemed to him moreartistic than mathematical; in applying themethod you had to rely on what you felt inyour bones.14) In the quotation given above,Davis conflates Turingery and Tuttes StatisticalMethod. It was the latter that required the pro-cessing of lots of dataso much, indeed, thatcarrying out the method by hand was com-pletely impractical. It was Tuttes method, notTuringery, that was implemented in Colossusand in its precursor, the Heath Robinson.19

I hope that Michies words will eliminate themyth that Turingery was implemented inColossus before it becomes set in stone:Turingery was not used in either breaking orsetting by any valve [vacuum tube] machine ofany kind (personal communication,November 2001).

Tutte has never received full credit for hisgreat achievement, which was the sine qua nonof the ensuing highly successful machine-baseddecryption of Tunny traffic. His method issometimes attributed to Turing and sometimesto Newman. This is Tuttes own description ofhis discovery:

Here was a method of wheel-setting! The pro-

cedure was not to be recommended as a hand

method but no doubt our electrical engineers

could find a way of mechanizing it. I went

into Gerry Morgans office [in the Research

Section, of which both Tutte and Newman were

members] to tell of these results. Max Newman

was there. They began to tell me, enthusiastical-

ly, about the current state of their own investi-

gations. When I had an opportunity to speak I

said, rather brashly, Now my method is much

simpler. They demanded a description. I must

say they were rapidly converted. The Research

Section urged the adoption of the Statistical

Method of wheel-setting.14

Flowers, Turing, and NewmanDaviss claim, quoted above, that Colossus

was essentially a physical embodiment ofturingismus is one of the ways in which heconveys the impression that Turing played aleading role in Colossus. Another is his refer-ence to Turings interest in the RCA cataloguein March 1943 and the juxtaposition of thiswith remarks introducing Flowers. The viewthat Turings interest in electronics contributedto the inspiration for Colossus is indeed com-mon. The claim is enshrined in more than oneleading museum; and in IEEE Annals of theHistory of Computing, Lee and Holtzman havestated that Turing conceived of the construc-tion and usage of high-speed electronic devices;these ideas were implemented as the Colossusmachines.20

By 1943, electronics had been Flowers driv-ing passion for more than a decade, and heneeded no help from Turing. As I mentioned, adefinitive contemporary account recorded thatColossus was entirely the idea of Mr. Flowers.2

Flowers emphasized in an interview with methat Turing made no contribution to thedesign of Colossus, saying: I invented theColossus. No one else was capable of doing it.21

Work on Colossus began early in 1943.(Turing was absent in the US; he left BletchleyPark for the US in November 1942.22) It tookFlowers and his team at the Post OfficeResearch Station 10 months to complete themachine, working day and night, pushingthemselves until (as Flowers said) their eyesdropped out. Colossus I successfully complet-ed its first trial runs on 8 December 1943.

At the Post Office Research Station before thewar, Flowers had explored the feasibility of usingvalves (vacuum tubes) as digital switches on alarge scale in telephone equipment. His work inthis area was, it appears, the earliest large-scaleuse of valves as devices for generating and usingbinary pulses.23 At this time, the common wis-




dom was that valves could never be used satis-factorily in large numbers, for they were unreli-able, and in a large installation too many wouldfail in too short a time. However, this opinionwas based on experience with radio receiversand the like, which were switched on and offfrequently. What Flowers discovered was that,so long as valves were left on, they could oper-ate reliably for very long periods. As Flowersremarked, at the outbreak of war with Germanyhe was possibly the only person in Britain whorealized that valves could be used on a large scalefor high-speed digital computing.24

Once Tutte had explained his StatisticalMethod to Newman, Newman suggested usinghigh-speed electronic counters to cope with thehuge amount of counting of binary coinci-dences that the method demanded.25 It was abrilliant idea, inspired by Newmans knowledgeof C.E. Wynn-Williams prewar work atCambridge on the electronic counting of -particle emissions.23 Turings contribution, inhis role as a scientific policy advisor, was to per-suade the Bletchley Park authorities that themachine envisaged by Newman should bebuilt.26 In December 1942, Newman was giventhe job of developing the requisite machinery.27

The result was the Heath Robinson, installed atBletchley Park in June 1943. Although thecounters were electronic, Heath Robinson waslargely electromechanical; the machine waseffective, but slow and unreliable. Newman wassufficiently encouraged to place an order formore Robinsons with the Post Office.

During the design phase of Heath Robinsonthere were difficulties with the logic unitthecombining unit in the terminology of 1942.The job had been given to F.O. Morrells tele-graph section at Dollis Hill, and it was proposedto implement XOR by means of a frequencymodulator of a type used for voice-frequencytelegraph signals.28 Because this device was ana-log, small variations would add up; wronganswers would often result.28 At Turings sug-gestion, Newman approached Flowers for help.Turing and Flowers had worked together previ-ously in connection with a relay-basedmachine for use against Enigma (this was notthe Bombe itself but a machine for automati-cally decrypting Enigma messages once the set-tings were known). Flowers and his switchinggroup improved the design of the combiningunit and manufactured it.29

Flowers did not think much of theRobinson, however. The basic design had beensettled before he was called in, and he was skep-tical as soon as Morrell (from whom he firstlearned of the Robinson) told him about it.30

The Robinson depended on keeping two papertapes, the message tape and the -tape, in per-fect synchronism as they were driven on pul-leys past a photoelectric reader at 1,0002,000characters per second. Flowers doubted that theRobinson would work properly, and inFebruary 1943 he presented Newman with thealternative of a fully electronic machine able togenerate the -stream (and - and -streams)internally.31 Opinion at Bletchley was that amachine containing the number of valves thatFlowers was proposing could not work reliably.Newman pressed ahead with the two-tapemachine, leaving Flowers to do as he wishedregarding his alternative proposal. On his owninitiative, working independently at Dollis Hill,Flowers began building the fully electronicmachine that he could see was necessary. Heembarked on Colossus in the face of scepti-cism from Bletchley Park and without theconcurrence of B.P.31

Colossus was not built under the directionof Flowers and Newman (as Davis, and folk-lore, assert). B.P. werent interested until theysaw it [Colossus] working, said Flowers.31

Flowers stated in an interview given in 1977:

I dont think they [Newman et al.] really under-

stood what I was saying in detailI am sure they

didntbecause when the first machine was con-

structed and working, they obviously were taken

aback. They just couldnt believe it! I dont

think they understood very clearly what I was

proposing until they actually had the machine.32

Not long before his death in 1998, Flowers


Work on Colossus began

early in 1943. It took Flowers

and his team at the Post

Office Research Station 10

months to complete the

machine, working day and

night, pushing themselves

until (as Flowers said) their

eyes dropped out.


spoke with sadness about the fact that credit forColossus was often given to Turing and toNewman. It is regrettable that erroneousaccounts continue to appear.

AcknowledgmentI am grateful to Diane Proudfoot, four anony-mous referees, and the editor, for commentsand advice.

References and notes1. Colossus is described in T.H. Flowers, The

Design of Colossus, IEEE Annals of the History of

Computing, vol. 5, no. 3, JulySept. 1983, pp.

239-252.

2. J. Good, D. Michie, and G. Timms, General Report

on Tunny, With Emphasis on Statistical Methods; in

the National Archives (Kew, Richmond, Surrey),

document reference HW 25/4 (vol. 1), HW 25/5

(vol. 2), 1945, p. 35. A digital facsimile of General

Report on Tunny is in The Turing Archive for the His-

tory of Computing; see http://www.AlanTuring.

net/tunny_report.

3. B.J. Copeland, ed., Letters on Logic to Max

Newman, The Essential Turing, Oxford Univ.

Press, 2004, pp. 204-216.

4. A.M. Turing, On Computable Numbers, with an

Application to the Entscheidungsproblem, Proc.

London Mathematical Soc., Series 2, vol. 42,

19361937, pp. 230-265.5. For an account of Turings life and work, see B.J.

Copeland, ed., The Essential Turing, Oxford Univ.

Press, 2004.

6. For more information about the ACE and the

DEUCE, see B.J. Copeland, ed., Alan Turings Auto-

matic Computing Engine, Oxford Univ. Press, 2004.

7. The story of Tunny and the Bletchley attack is

revealed in the recently declassified (2000) Gen-

eral Report on Tunny in Ref. 2. A digital facsimile

of the complete report is available on the

authors Web site at

http://www.AlanTuring.net/tunny_report.

8. The Tunny machine was manufactured by the

Lorenz company, the first model bearing the des-

ignation SZ40 (SZ stood for

Schlsselzusatzgert, meaning cipher attach-

ment). A later version, the SZ42A, was

introduced in February 1943, followed by the

SZ42B in June 1944 (40 and 42 perhaps refer

to years). The physical machine is described in sec-

tion 11 of the General Report on Tunny and in D.

Davies, The Lorenz Cipher Machine SZ42, Cryp-

tologia, vol. 19, 1995, pp. 517-539; the machines

function and use is described in sections 11, 94, et

passim, General Report on Tunny.

9. M. Davis, The Universal Computer: The Road from

Leibniz to Turing, Norton, 2000, pp. 174-175.

10. J.A.N. Lee, Computer Pioneers, IEEE CS Press,

1995, pp. 306, 671.

11. Ibid, p. 492.

12. E. Enever, Britains Best Kept Secret: Ultras Base at

Bletchley Park, 2nd ed., Alan Sutton, 1994, pp.

36-37.


on Tunny, 1945, p. 458.

14. W.T. Tutte, My Work at Bletchley Park, 2000.

To appear in Colossus: The First Electronic Comput-

er, B.J. Copeland, ed., Oxford Univ. Press, 2005.


on Tunny, 1945, pp. 313-315.

16. A Cryptographic Dictionary, Government Code

and Cypher School, Bletchley Park; in the US

National Archives and Records Administration

(College Park, Maryland), document reference

RG 457, Historic Cryptographic Collection, box

1413, NR 4559, p. 89. A digital facsimile of A

Cryptographic Dictionary is in The Turing Archive

for the History of Computing; see http://www.

AlanTuring.net/crypt_dic_1944.


on Tunny, 1945, p. 313.

18. The reasoning is as follows. Let p1 and p2 be the

first and second impulses of the plaintext and let

(p1 + p2) mean the result of differencing (p1 + p2). Then the above account of the work-

ings of the Tunny machine implies that (c1 + c2) =(p1 + p2) + (1 + 2) + (1 + 2). Tunny addi-tion has the property that x + = x for either

value of x, dot or cross. So, since (p1 + p2) and(1 + 2) are predominantly dot, (c1 + c2) and(1 + 2) must agree with one another moreoften than not.

19. See further B.J. Copeland, Colossus and the

Dawning of the Computer Age, Action This Day,

R. Erskine and M. Smith, eds., Bantam, 2001, pp.

342-369.

20. J.A.N. Lee and G. Holtzman, 50 Years After Break-

ing the Codes, IEEE Annals of the History of Com-

puting, vol. 17, no. 2, Spring 1995, pp. 32-43. The

quotation is from p. 33.

21. Flowers in interview with Copeland, July 1996.

Except where indicated otherwise, all material in

this article relating directly to Flowers derives

from Flowers in interviews with Copeland,

19961998; and Flowers in interview with

Christopher Evans in 1977 (The Pioneers of

Computing: An Oral History of Computing, Sci-

ence Museum, London).

22. S. Turing, Alan M. Turing, Heffer, 1959, p. 71.

23. C.E. Wynn-Williams was among the first to suggest

that electronic valves be used in place of relays, in

connection with the counting of -particle emis-

sions; see C.E. Wynn-Williams, The Use of Thyra-

trons for High Speed Automatic Counting of

Physical Phenomena, Proc. Royal Soc., Series A,

vol. 132, 1931, pp. 295-310. (See also A.W. Hull,




Hot-cathode Thyratrons, General Electric Rev., vol.

32, 1929, pp. 390-399; and N.A. de Bruyne and

H.C. Webster, Note on the Use of a Thyratron

with a Geiger Counter, Proc. Cambridge Philosoph-

ical Soc., vol. 27, 1931, pp. 113-115.)

In 1931, Wynn-Williams reported (p. 302) that

rings of three and four valves had been tried out

experimentally. In contrast, Colossus I contained

approximately 1,600 valves and the later Colossi

approximately 2,400.



on Tunny, 1945, pp. 33, 458.

26. D. Horwood in interview with Copeland, October

2001.


on Tunny, 1945, pp. 28, 33.

28. H. Fensom, How the Codebreaking Colossus

Was Conceived, Built and Operated: One of its

Engineers Reveals its Secrets, 2001. To appear in

Colossus: The First Electronic Computer, B.J.

Copeland, ed., Oxford Univ. Press, 2005.

29. Flowers in interview with Copeland, July 1996;

see also J. Good, D. Michie, and G. Timms, Gen-

eral Report on Tunny, 1945, p. 33.



32. Flowers in interview with Christopher Evans, 1977.

Jack Copeland is a full profes-

sor of philosophy and mathe-

matical logic at the University

of Canterbury, New Zealand,

and director of The Turing

Archive for the History of

Computing. He studied mathe-

matical logic at the University

of Oxford under Turings student Robin Gandy. He has

published numerous journal articles, and his books

include Artificial Intelligence: A Philosophical Introduction

(Oxford: Blackwell, 1993, second edition forthcom-

ing). He is editing three books for Oxford University

Press: The Essential Turing (2004), Alan Turings

Automatic Computing Engine (2004) and Colossus: The

First Electronic Computer (2005). He has held universi-

ty positions in Britain, Australia, and New Zealand,

and visiting positions in the US and Denmark.

Readers may contact Jack Copeland at The Turing

Archive for the History of Computing (www.

AlanTuring.net), Univ. of Canterbury, Private Bag

4800, Christchurch, New Zealand; jack.copeland@

canterbury.ac.nz.

For further information on this or any other com-

puting topic, please visit our Digital Library at

http://computer.org/publications/dlib.



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