Brigadier John Tiltman

A Giant Among 

Cryptanalysts
Cover Photo:

John Tiltman in uniform, 1942

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Brigadier John Tiltman: 

A Giant Among 

Cryptanalysts

Center for Cryptologic History

National Security Agency

2007
This publication is a product of the National Security Agency 

history program. It presents a historical perspective for informational and educational purposes, is the result of independent research, and does not necessarily reflect a position 

of NSA/CSS or any other U.S. government entity
4

Brigadier John Tiltman has been variously described as the 

greatest cryptanalyst of his time, the best cryptanalyst ever to work 

for Government Communications Headquarters (GCHQ, Great 

Britain’s counterpart to NSA), and a “legend in his own time.” 

He led the attack on numerous code and cipher systems of over a 

dozen countries. At the same time, he developed cipher systems for 

his own country that were unbreakable during the time they were 

used. He held the title of Chief Cryptographer for the Government 

Code and Cypher School (GC&CS, which became GCHQ in 1946) 

from 1942 on. He humbly described this position as “honorary,” 

but it carried the dual responsibility of being tasked with the initial 

diagnosis of and attack on all unbroken foreign cipher systems, 

and the development of secure ciphers for British forces. 

His career spanned two world wars, conflicts in Korea and 

Vietnam, and most of the Cold War. Retiring from GCHQ in 1964, 

he capitalized on relations he had built up over the previous two 

decades and served as a consultant to NSA until 1980. At the 

age of eighty-five, he finally stepped away from sixty-six years of 

public service to two countries. Sixty of those years were devoted 

to signals intelligence (SIGINT) and communications security 

(COMSEC). To those who worked with him, he was known simply 

as “The Brig.”

Early Years

John Hessell Tiltman was born in London on 25 March 

1894. He attended Charterhouse School and early on showed the 

intellectual prowess that would mark his career. At age thirteen, he 

was offered a place at Oxford. He was unable to accept the position 

because the recent death of his father had changed the family’s 

circumstances to a degree that made attendance at university 

a luxury they could not afford. Upon leaving school in 1911, he 

became a teacher, another early indication of a lifelong tendency, 

this one to educate those around him. 
5

Whatever aspirations Tiltman had towards a “normal” life 

of teaching and continued learning were interrupted abruptly, 

as were the varied ambitions of his generation, by the outbreak 

of World War I in 1914. Heeding the call of patriotism that 

moved millions across the European continent, he enlisted in 

September 1914. He received a temporary commission (which 

became permanent in 1916) in the King’s Own Scottish Borderers. 

He served with distinction, being wounded in 1917 and receiving 

the Military Cross for valor.

In 1919, while still recovering from his wounds, he was attached 

to the British Military Mission that was sent to Irkutsk in Siberia. At 

that time Britain, along with several other of the recently victorious 

allies (including France, the U.S., and Japan) sent contingents of 

troops to parts of Russia following the Bolshevik Revolution in 

October/November 1917. Their purpose was twofold: to keep 

supplies the allies had sent to the tsarist government for the 

common fight against Germany from falling into Bolshevik hands, 

and to support the counterrevolutionary forces (White Russians) 

formed to overthrow the newly established Communist (Red) 

regime. Tiltman believed that he was selected because he had 

picked up a smattering of Russian during his teaching days. 

His Siberian tour was cut short because he had not yet fully 

recovered from his war wounds. He estimated that he was able to 

spend only about six weeks actually working out of the two and 

a half months he spent in Russia. The fact that he undertook to 

inspect a course set up to train officers for the White armies, a task 

that involved an eight-mile roundtrip walk in the dead of Siberian 

winter (with temperatures around sixty-one degrees below zero 

Fahrenheit, and a stiff wind to boot) did nothing to improve his 

health. In fact, it led to his being hospitalized in Vladivostok. From 

there he was evacuated back to Britain. 

Nonetheless, this brief tour allowed him to reinforce his 

language skills sufficiently to be selected to attend a Russian 

course for Army officers at King’s College in London starting in 

March 1920. Tiltman never considered himself to be a linguist, as 
6

he found languages hard to acquire, but he was far enough ahead 

of his fellow students that he spent most of the course teaching 

himself and not actually attending class. At the conclusion of the 

course, he tested successfully as a second-class interpreter. This 

success would, under normal circumstances, have entitled him 

to a three-year tour in Russia to hone his newly acquired skills. 

Great Britain and the nascent Soviet Union did not, however, have 

diplomatic relations, so such a tour was out of the question.

Instead, he was seconded to the War Office and sent to work at 

GC&CS to help deal with a backlog of Russian diplomatic decrypts. 

GC&CS had been formed after World War I from the naval effort 

in the Admiralty and the military one at the War Office. When 

Tiltman joined, it was located in Watergate House on the Thames 

Embankment near Charing Cross. Its head, who would serve until 

1945, was A. G. Denniston. His deputy was E. W. Travis, who 

would replace Denniston as head of the Bletchley Park effort in 

1942 and continue until 1952. Tiltman’s secondment was to have 

lasted for two weeks. It resulted in a career change that lasted for 

sixty years.

Tiltman quickly demonstrated a proficiency in dealing with 

Russian ciphers, so the two-week assignment was extended at first 

to a year during which time he slowly evolved from an interpreter 

into a cryptanalyst. He worked under the direction and tutelage of 

Ernst Fetterlein, an amazing story in his own right. Fetterlein had 

been the chief cryptanalyst for the Russian tsarist government, 

holding the ranks of both admiral and general. Following the 

Bolshevik Revolution, he walked across the Finnish border and 

made his way to Great Britain where he became a naturalized 

British citizen and went to work for GC&CS. 

In Tiltman, Fetterlein must have recognized a kindred spirit. 

Tiltman later recalled that Fetterlein took him under his wing. He 

became the only person (in an office of six or seven) the Russian 

would actually take the time to train in cryptanalysis. Even then, 

there was no formal training involved, just useful hints on how 

to identify types of ciphers and attacks that would prove useful 
7

against them. It was all very much in the nature of on-the-job 

training. In later years, Tiltman in a way repaid the debt he owed 

his early mentor. In 1935 he recruited Ernst’s brother to work for 

GC&CS, and also brought the brother’s son into the business.

Tiltman later described the Russian ciphers he dealt with as 

low-grade simple columnar transposition systems with key that 

changed with each message. In 1921 the Russians changed the 

system and began using dinome substitution underneath the 

transposition. Since they continued using the old keys, the system 

broke fairly easily.

Then in March they introduced an entirely new system with 

new keys, and some effort was required to break in. The British 

were assisted by a lazy code clerk (not the last time Tiltman would 

be able to use this advantage), who, in effect, defeated the system 

by not using all the possible variants available to him. The system 

was built so that each vowel could be substituted for by seven 

different dinomes that would reduce the chance that repetitions 

would reveal the frequency count cryptanalysts use to wedge 

their way into a cipher. In one particular message, however, a 

single word (the Russian dogovor, “treaty”) appeared multiple 

times. Each time, the less-than-diligent clerk used the same vowel 

dinomes rather than the variants. With that edge, Tiltman worked 

out the cipher system.

His next lesson in the world of ciphers involved finding 

the method used to determine the transposition keys so that 

exploitation could become essentially routine. It soon became 

clear that the keys were derived from lines of poetry, but it took 

some time to uncover that the author was an obscure midseventeenth century English poet. Tiltman then had to find the 

book or anthology that was being used. Through resourceful 

digging he found the book, an out-of-print edition of the poet’s 

works held by the British Museum. That venerable institution then 

invoked a strict interpretation of the law which forbade removal of 

works it held to block the request of GC&CS to borrow the book 

and copy it, questions of national security notwithstanding. It took 
8

the personal intervention of the director of GC&CS to convince 

the British Museum to allow a one-shilling book (a shilling being 

1/20th of a British pound and worth at that time about 50 cents in 

U.S. currency) to be borrowed, even though this was “breaking the 

law of the land.” 

Tour in India 

Then, in September 1921, Tiltman was assigned to the General 

Staff of British Indian Army Headquarters in Simla, India, to 

replace the officer in charge, one Colonel Jeffery. The original 

intent had been to post Tiltman as the assistant military attaché 

in Meshed, Iran, where an effort was already under way to 

exploit Russian ciphers. This posting would have involved mostly 

translation work. The British powers-that-be realized that this 

would be a waste of the cryptanalytic talents Tiltman was already 

demonstrating. So plans were altered, he went to Simla, and the 

Meshed project was dropped. He was to remain in this position 

as an army captain until 1925. Following the first of what would 

prove to be numerous retirements, he continued doing the same 

job as a War Office civil servant (with the title “Signal Computor”) 

until 1929.

In his new posting, Tiltman had to overcome unexpected 

opposition. The original intent had been that he would replace 

Colonel Jeffery since that officer had opted to retire rather than 

face a mandatory posting to the regiment he nominally belonged 

to, but in which he had never actually served. While Tiltman was 

en route to Simla, Jeffery changed his mind and opted to remain 

in the service. His decision was made easy since the British Army 

elected to allow him to remain in his job at Simla and not force a 

return to his regiment (one can imagine that the regiment itself felt 

some relief with this change of heart since it would have been put 

in the position of receiving a senior officer who knew nothing of its 

traditions and practices). When Tiltman arrived, tension between 

the two was almost instinctive. 
9

Jeffery had begun his career by spending three years in China, 

“gone native” as the British used to put it. He traveled extensively 

throughout the country becoming, in the process, a first-rate 

Chinese linguist and scholar. He was then posted to South Africa 

and placed in charge of Chinese coolies working in the mines 

there. In 1912 he landed in India on the intelligence staff. There, 

without any formal training, he built up a library on Chinese codes. 

Having worked for years in isolation on the Chinese problem, he 

believed he had essentially invented the process of breaking into 

Chinese systems on his own. Into his world now stepped Tiltman, 

who later admitted that his own brashness and conceit did nothing 

to smooth the transition. Jeffery left for a year’s leave with the two 

barely on speaking terms. The situation did not improve upon 

his return in 1922, and friction between the old hand and the new 

“upstart” threatened to disrupt the entire mission. Tiltman learned 

to keep his distance, a task made easier since his work involved 

Russian intercept. Jeffery preferred to continue working Chinese 

systems, and adamantly refused to learn Russian.

Over the next several years, the two learned to overcome 

their initial differences and developed a respect for each other’s 

professional skills. Jeffery would eventually be forced into 

retirement in 1935, suffering from double cataracts. With tensions 

mounting in Europe in 1938, his skills were needed, and it was 

Tiltman who persuaded him to return to service, this time with 

Tiltman as senior, in spite of misgivings on Jeffery’s part that his 

recently repaired eyesight (he had had the cataracts surgically 

removed by 1938) might suffer from the strain of cryptologic 

work. It is a tribute to both men that they had overcome whatever 

differences plagued their initial relationship to the point where 

they liked and respected each other enough to put their skills to 

work for the greater good. 

During the assignment in Simla, Tiltman sharpened the skills 

that would make him one of Britain’s premier cryptanalysts. 

The job was to gather and analyze Russian diplomatic messages 

being sent between Moscow, Tashkent, and Kabul. Given the 

small size of the British effort (never more than five individuals 
10

in the 1920s), Tiltman became involved in all aspects of the 

problem. This included directing the intercept, encouraging the 

intercept operators at various collection sites on the Northwest 

Frontier, performing rudimentary traffic analysis, diagnosing the 

cipher systems (which frequently changed), stripping the long 

additive keys, recovering the underlying code books, translating 

the messages, and then arguing the significance of the messages 

with the Intelligence Branch. In addition, he wrote not only 

reports on individual events, but also summary reports. In short, 

circumstances led him to become proficient in virtually every 

aspect of the SIGINT business.

In later life, he insisted that this broad-based background was 

key to his further development, and gave him a deep appreciation 

for all aspects of the cryptologic problem. Though he came to 

recognize that modern specialization had its place, and made 

experiences such as his virtually impossible to replicate, he felt 

that younger generations of cryptanalysts could only suffer a loss 

of proficiency as a result.

Throughout this period, the Russians continually upgraded the 

cipher systems they were using, becoming increasingly sophisticated 

in their use of additives. The British, led by Tiltman, were able to 

keep up with the changes until 1928 when the Soviets introduced 

one-time pads, and their systems became essentially unreadable. 

He later recalled a couple of memorable incidents stemming from 

his successful efforts. In 1925 the British were facing another in a 

never-ending series of incidents along the Northwest Frontier, this 

time in Waziristan (located on the present-day border between 

Pakistan and Afghanistan), and mounted an expedition to deal 

with the problem. This prompted a message from the Soviet 

ambassador in Afghanistan to Moscow asking for instructions. The 

message was translated (and forwarded to British authorities in 

India) as asking what the Soviets contemplated doing “with a view 

to the occupation of Waziristan.” 

The implication that the Soviets might intend to send troops 

into an area the British considered their own raised the collective 
11

blood pressure in New Delhi and Simla. Fortunately those in charge 

realized the logistical impossibilities involved in moving forces 

rapidly over the Hindu Kush (the mountain range that effectively 

separates Afghanistan from Pakistan), and asked that the message 

be rechecked. That task fell to Tiltman, whose language skills 

were admittedly inferior to those of the original translator, but 

whose attention to detail and standards of accuracy were infinitely 

greater. He quickly recognized that the proper translation was 

“in view of the occupation of Waziristan.” In other words, the 

ambassador wanted to know how Moscow wished him to react to 

the British occupation. Blood pressures returned to normal, and 

Tiltman now had an extra job, that of checking and correcting all 

Russian translations coming out of the effort in Simla.

The second incident involved a lost opportunity. The British 

learned that the Soviets had two cipher clerks in Kabul, Kotlov 

and Serafimovich. Because of recurring accuracy problems the 

Soviets experienced with the two, an order came down from 

Moscow insisting that all messages be signed in cipher by the 

clerk responsible for enciphering and sending the message. This 

provided Tiltman with a very useful crib for breaking into the 

ciphers used. Eventually, however, a message was intercepted 

instructing Serafimovich to return to Moscow since his papers 

were not in order. In the Soviet Union of 1926, there could be only 

one outcome of such a summons, and Serafimovich was well aware 

of what it would be. He fled at once to the British embassy, but 

was promptly ejected. Tiltman notes that he was never heard from 

again. Tiltman lost a useful message string that he had been using 

to break into Russian messages. The British lost the opportunity 

of debriefing an individual who had intimate knowledge of the 

various ciphers in use by the Soviets. 

As if his various responsibilities on the SIGINT side of the 

business were not enough, Tiltman was also charged with creating 

practical ciphers for British use. He created a system that he 

believed was secure, improving on systems already in use. Typical 

of the man, however, was his continued study of the problem and 

eventual recognition that he had built flaws into his system which 
12

could be exploited. He used this lesson for two purposes. First, 

it allowed him to strengthen future systems he would be called 

on to create. He often pointed out that during the years when he 

was asked to create ciphers, no organized process existed to test 

the strength of any system before it was put into use. Only the 

diligence of the maker and his determination to follow up on his 

creation made the difference between a cipher that was vulnerable 

to exploitation and one whose weaknesses could be recognized and 

fixed.

The second advantage he gained was that he was able to use 

the knowledge he acquired to attack similar systems built by 

adversaries. He maintained that sloppy thinking would reveal 

itself faster in the development of ciphers than in just about any 

other field. Because of that, he found the practice of building 

ciphers to be useful in training the imagination for the diagnosis 

of complicated problems. One of his fundamental beliefs was that 

the livelihood of a cryptanalyst depends almost entirely on the 

overingenuity of the designers of foreign ciphers.

Creation of the Military Section, GC&CS 

In 1930 Tiltman was called back to Britain to set up the 

Military Section of GC&CS. The effort started with two permanent 

staff including Tiltman, and three trainee regular officers who 

were seconded to GC&CS for tours ranging from three to four 

years generally before deployment to the main Army Middle East 

station, at Sarafand in Palestine. Eventually, clerical support came 

in the form of the wives of the officers assigned to the section. 

While it was hoped that this would be a temporary solution, the 

help turned out to be more transitory than expected. The assistance 

of most of the wives lasted only a few months. A notable exception 

was Tiltman’s own wife, Tempe, who stayed on until 1939.

The War Office had pushed to have this section created with 

the intent that it would concentrate its efforts on working against 

military ciphers. Due to limited collection resources, and the 

state of European relationships in the early 1930s, there was an 
13

extremely limited amount of military-related intercept available 

for use (to include training), so Tiltman resorted to gathering 

traffic that the other sections in GC&CS had either no time for 

or no interest in. This insistence on working whatever material 

was available, even if it had nothing to do with the military, led to 

some difficulties with the War Office. He pushed ahead, able to see 

that having cryptanalysts experienced at working with high-grade 

cipher systems would prove beneficial in the future. He would just 

have to allow the passage of time to convince those in the War 

Office who disagreed with the logic of his arguments. 

As a result, he spent a good deal of time from 1931 to 1935 

working Comintern (the Communist International, an organization 

established by Moscow to control worldwide communist parties) 

traffic. The network his section was interested in was centered in 

Berlin, with links to London, Paris, Amsterdam, Vienna, Rome, 

and some locations in the Far East. They also exploited a related 

Moscow-to-Berlin link. The network used a codebook plus novels 

to generate running key for encipherment purposes. So once 

again, as at the beginning of his cryptologic career, Tiltman found 

himself in the hunt for obscure literary works. His group found 

that the books used were primarily in German, though the London 

link used English language novels and collections of poetry.

 Eventually, through many trips to book dealers and libraries 

in London, Berlin, Amsterdam, and other European cities, Tiltman 

tracked down the various books used by the London link and 

several used by the others in the network as well. He noted that 

one particular problem he encountered on more than one occasion 

involved a difference in editions. He and his group kept assuming 

that the books used in London would be British editions. It turned 

out that in some instances the Comintern agents opted to use 

American editions. These generally had different pagination and 

even, in the case of poetry collections, contained different poems. 

His work paid off, however, as it provided insight into Comintern 

efforts (or at least wishful thoughts, as very little subversion was 

ever actually proven) aimed at subverting members of the British 
14

armed forces. Efforts were made, successfully in the final analysis, 

to locate the British end of these transmissions. The effort was 

hindered by the fairly primitive direction finding equipment 

available at the time. Nonetheless, A.G. Denniston, head of GC&CS, 

considered this effort to be his organization’s most successful 

operation of the 1930s.

His work on this problem led to his initial contacts with the 

French, and here he gave a preview of the skills that would later 

serve him so well in establishing a close working relationship 

with the Americans. He was sent to Paris to discuss mutual 

exploitation of Russian ciphers, but was instructed to avoid giving 

away anything the British had learned about Russian use of long 

additive streams or one-time pads. As he and the leader of the 

French contingent, Gustave Bertrand, were about to begin the 

ritual dance to determine who knew what, Bertrand immediately 

indicated that he knew where British sensitivities lay. He handed 

Tiltman a paper that contained exactly what the French knew, 

setting aside any qualms Tiltman’s instructions may have caused. 

Tiltman responded to this openness in kind, and a relationship was 

established that served the British well throughout the decade as 

both countries grappled with matters of more immediate concern 

than Russian Comintern intrigues. The cooperation established in 

this exchange led to frank exchanges in dealing with the German 

Enigma machine.

The work done against the Comintern network, as indeed all of 

the cryptologic work done through the 1930s and in later years by 

Tiltman, was done by hand, with virtually no machine assistance. 

Tiltman remembered that in 1931-32 he had been asked by 

Denniston to visit the British Tabulating Machinery Company 

(BTM, the British licensee for IBM) to investigate the work they 

were doing on machines that might have a cryptologic application, 

especially in the field of sorting large volumes of data. He was 

singularly unimpressed, largely because the machines were so 

primitive that he could outperform them. He later admitted that 

this caused him to fail to recognize their potential, and to dismiss 

them. In his view, GC&CS delayed beginning to work with and 
15

influence the development of machines that would eventually lead 

to the computer age until the issue was forced on it at the beginning 

of World War II. This probably represents an oversimplification 

on his part, as other sections of GC&CS, and Tiltman himself, 

worked closely with BTM and others, setting the stage for its great 

successes against German machine systems during the war. 

As the 1930s progressed, the international scene shifted to one 

that was more threatening. The decade began with Britain facing an 

impoverished and disarmed Germany while being allied with the 

continent’s dominant military force, France, as well as with Italy, at 

least nominally. The Soviet Union, while posing a rhetorical threat, 

was in the throes of a series of domestic turmoils that included 

collectivization, rapid industrialization, and seemingly endless 

internecine purges. These effectively rendered her, temporarily 

at least, a nonfactor in European power politics. In the Far East, 

Japan’s expansionistic tendencies had not yet taken on an overt 

aggressiveness outside of Manchuria. The presence of elements of 

the British fleet in the region appeared to have that situation well 

under control.

By mid-decade, however, the situation had changed 

dramatically. Germany was in the control of the rabidly nationalistic 

National Socialist (Nazi) party, and had embarked on aggressive 

rearmament, denouncing the treaty system that had ended World 

War I. Italy had begun a policy of expansion into areas that 

threatened British communication with essential parts of her 

empire. Japanese expansive ambitions in the Pacific could no 

longer be disguised or complacently ignored. France still appeared 

to be the dominant military force in Europe, but her position was 

being increasing undermined by economic depression and internal 

political turmoil.

What this meant for Tiltman and his Military Section at GC&CS 

was that there was no longer a dearth of material with which to 

work, although the communications practices of the German 

forces meant that British interception of messages enciphered 

using the version of the Enigma machine adopted by the German 
16

General Staff was limited. Tiltman conducted some investigations, 

solving the indicator system used by the Germans, but (unlike the 

Polish cryptanalysts led by Marian Rejewski) neither he nor his 

colleagues successfully attacked the machine itself. The British 

enjoyed some success against a less complicated variant of the 

Enigma used by Italian and Fascist forces during the Spanish 

Civil War. The major player in this effort was Alfred Dillwyn 

(“Dilly”) Knox. Tiltman himself meanwhile began to concentrate 

on Japanese systems. There was still a general lack of German 

traffic, and Italian systems were handled by others in his section. It 

was, in fact, Italian military action, in Ethiopia (Abyssinia) in 1935, 

that led to the first expansion of the section with the addition of 

three officers, one an Italian linguist. 

With others in his section dealing with the Italian problem, 

Tiltman was left free to concentrate on Japanese systems, 

particularly those used by Japanese military attachés. In 1933 

he solved a system the attachés had been using since 1927. To do 

this, he had to teach himself the rudiments of Japanese on the fly, 

as it were. His success ran him head on into a prejudice he would 

reencounter during World War II. Prior to his breakthrough, the 

problem had been in the hands of two classically educated retired 

career diplomats who had served in Japan as consuls general 

and who knew the language. They had some degree of difficulty 

accepting that Tiltman, a self-taught linguistic amateur who had 

never set foot in Japan, could succeed where they had failed. 

Tiltman moved on to work other Japanese military systems, 

concentrating on army traffic which was being provided by British 

sites in Hong Kong. His innate skills were complemented by 

Japanese misuse of their systems, and this enabled him to break 

first the indicating system in use and then the additive systems used 

to encipher the underlying code. By 1937 he believed that he had 

made enough progress in the system that it could be handed over 

to others to work. Particularly, he wanted the Far East Combined 

Bureau (the British joint service codebreaking and intelligence 

center, then in Hong Kong) to take up the work since they were 

closer to the immediate customer of the resulting product. The 
17

Japanese practice of changing the substitution tables that were 

the heart of their system every six to nine months coupled with 

the inexperience and lack of confidence of the individuals in Hong 

Kong frustrated his plans for the moment.

Not every venture of his at this time was an unqualified 

success. Years later he enjoyed telling the story of how in 1935 

he spent weeks working on what he thought was a batch of 

Japanese military intercepts forwarded by Hong Kong. He quickly 

established that he was working on unenciphered code, and 

began to break out the groups that stood for numbers. He found it 

curious that the numerical order of the code groups followed the 

stroke order in which the corresponding Chinese characters were 

written. He was hard at work, and quite a ways along, feeling good 

about his progress, when a friend who was a Chinese interpreter at 

the War Office looked at what he had and told him that he had just 

“broken” the publicly available Chinese Standard Telegraph Code 

(the telegraphic code used to render Chinese ideograms into text 

that could be sent over the “wires”). The experience was not lost 

on him, as we shall see.

On a more serious note, Tiltman continued his work against 

Japanese systems, moving to naval cipher systems in 1939. In 

that year he broke the additive system used by the latest Japanese 

Navy system, which would come to be designated JN-25 by the 

Western allies. This enabled him to begin stripping the cipher 

from the underlying code groups. Recovery of those code groups 

was then necessary before the actual messages could be read, and 

that process, as we shall see, was equally daunting. He credited his 

success to similarities between the naval additive system and the 

military ones which he had been successfully exploiting for several 

years. 

A historical aside is called for at this point. Students of 

American cryptology are well aware that U.S. Navy cryptologists 

of OP-20-G were also independently working on Japanese naval 

codes and ciphers. Their effort suffered from extremely limited 

resources and was marked by hesitant success up to and through 
18

the Japanese attack on Pearl Harbor. Reading the JN-25 code 

would have provided invaluable insight into Japanese naval plans 

for that attack, just as it provided the key intelligence that enabled 

the U.S. Navy to plan its successful ambush of the Japanese 

Imperial Fleet at Midway in 1942. 

Tiltman’s breakthrough against JN-25 in 1939 should not be 

seen as food for the conspiracy theorists, who believe, among other 

things, that Britain had foreknowledge of the Pearl Harbor attack 

which was withheld so as to draw the U.S. into the fight. Breaking 

through the additive system used for encipherment (Tiltman’s 

accomplishment, achieved independently by U.S. cryptanalysts 

as well) was just the first step needed for full exploitation of the 

information contained in Japanese naval messages. The underlying 

codebook then had to be recovered, a tedious and painstaking 

process where the progress of months of work could be and was 

undone in an instant by changing the book. Work could also be 

set back by changing the additive keybook used to encipher the 

code. The Japanese Navy was appropriately security conscious and 

changed its codebooks and its additive keys periodically (the actual 

codebook was revised once, the additive book six times between 

the time JN-25 was introduced and Pearl Harbor). This forced 

U.S. and British analysts to start from zero when the codebook 

was changed and set them back, though not as severely, each time 

the additive book was changed. Neither of the soon-to-be AngloSaxon allies had made sufficient progress into the codebook in use 

in late 1941 to predict the attack on Pearl Harbor (less than ten 

percent of the 50,000 entries in the codebook then in use had been 

recovered).

The year 1939 also marked Tiltman’s success in an endeavor 

he had been working at since 1937. In that year he was finally 

able to shift responsibility for day-to-day work on the Japanese 

military systems to Hong Kong. He had come to find that keeping 

up with the changes the Japanese made every few months was 

consuming too much time, and his efforts were hampered by 

the lack of Japanese linguists assigned to the problem. He had 

solved the underlying technique. The everyday exploitation could 
19

now be handed over to individuals who were both closer to those 

who needed the intelligence and more adept at the language. He 

transferred a couple of cryptanalysts he had trained to Hong Kong, 

and did not again become involved with Japanese military systems 

until 1942.

He would make one additional major contribution in the first 

years of the war to the British effort against Japanese cryptologic 

systems. When Britain joined the U.S. in declaring war on Japan, 

he and other GC&CS leaders recognized that they were faced with 

an acute shortage of Japanese linguists. The estimate provided by 

language experts was that it would take at least three years to train 

linguists, a period that was completely unacceptable given the time 

pressures at play. Tiltman believed the job could be done in much 

less time, acknowledging that he was not looking for capabilities 

in the spoken language, and that the vocabulary that needed to be 

mastered was limited and stereotyped. He estimated six months 

was all that was needed. 

He got permission from his superiors to proceed, recruited a 

retired naval officer as an instructor, and set up classes in rooms 

above a gas company’s showroom in Bedford, about fifteen miles 

from Bletchley Park. His experiment was a great success, producing 

numerous cryptolinguists whose skills, while by no means enabling 

them to converse at native-speaker level, were sufficient for the job 

at hand. They filled positions not only in GC&CS, but also in the 

Foreign Office and with the Indian government. The criticisms he 

received about the abilities of graduates of the course dealt with 

their lack of knowledge of spoken Japanese, and with the fact that 

they were not Far Eastern scholars, hence could not be relied on 

to extract subtle nuances of the language. Since the training was 

not intended to develop skills in either of those areas, Tiltman 

generally left such critiques pass without comment.

The year 1939 was, of course, momentous for more than Tiltman’s 

successes against Japanese naval and military cryptosystems. As 

war broke out, the Military Section he headed expanded rapidly. By 

1939 it had grown from its original four to about ten. In addition to 
the modest increase in strength it received with the outbreak of the 

Italian campaign in East Africa, 1938 had seen it gain a few more 

clerks and experienced operators. During the war it would grow 

to nearly two thousand. Tiltman recalled that by 1939 real results 

of efforts to increase the manpower available to GC&CS (begun in 

previous years) were becoming evident. One example he pointed 

to was a week-long general indoctrination course (in which he was 

one of the lecturers) set up for twenty-four scholars from Oxford 

and Cambridge who had been placed in reserve status, ready 

to be called to duty when needed. His impression was that this 

group included such future GC&CS stars as Alan Turing, Gordon 

Welchman, and Hugh Alexander (though here his memory may 

have failed him since Hugh Alexander was a graduate of King’s and 

was not associated with Oxford or Cambridge).

Return to Military Service

Tiltman himself was recalled to active military duty, with the 

rank of lieutenant colonel. The move was made primarily so that 

he would have official status in dealing with the French military 

cryptologic system, a group he liaised with several times before the 

collapse of the French military in June 1940. He was now in charge 

of Number 4 Intelligence School (the British, like the Americans, 

liked to hide their cryptologic efforts behind euphemisms) which 

consisted of his own Military Section, now located at GC&CS’s 

wartime home in Bletchley Park, and a large number of traffic 

analysts in London.

The elements of GC&CS that supported the military, air, and 

naval efforts had been moved to Bletchley Park in mid-August just 

before the war broke out, and the rest of the organization followed 

shortly thereafter. Their former home in the Broadway buildings 

across from St. James Park Underground Station was considered 

both too small and too vulnerable to air attack. So, GC&CS moved 

to the former estate of the owner of a chain of tobacco stores, 

some fifty miles north of London, an area considered safe from the 

anticipated German air assault. Tiltman noted after the war with 

some sense of irony that the move actually placed GC&CS within 

20
a quarter mile of railroad marshalling yards, a prime target in 

the coming air war. Fortunately, Bletchley Park was bombed only 

once, with negligible damage, probably as a result of a German 

pilot jettisoning his bomb load while trying to escape British 

fighter aircraft. 

In dealing with the large influx of new people brought on by 

the war, Tiltman wanted to avoid the situation he had faced at the 

beginning of his own cryptologic career when he had been pretty 

much left to his own devices to learn the business. As he described 

his first days at GC&CS, he was sat down, shown a cipher, and told 

to get to work breaking it. While that approach might work with 

selected individuals, especially when they enjoyed the luxury of a 

peacetime environment, he recognized it as a recipe for disaster if 

applied generally and under the pressures of wartime. So he set up 

a basic cryptanalysis course for new people to introduce them to 

the fundamentals of the trade. But he did not believe that training 

could go beyond enhancing skills that had to be innately present. 

All training could do was stimulate intelligence and imagination. 

In his view, cryptanalysts were born, not made.

Relations with the French 

As we have seen, Tiltman’s resumption of military rank 

was done largely to facilitate his dealings with the French, a 

relationship that had begun in May 1933 when he was working 

the Comintern problem. He resumed his close cooperation with 

Bertrand, even gaining access to the areas where the French were 

working on Enigma. Although both the French and the British 

benefited from work done by the Poles, each was rather reticent 

about fully sharing its efforts at exploitation with the other. 

Bertrand continued to amaze Tiltman with his uncanny ability to 

foresee where a discussion was going, a trait that enabled him to 

head off embarrassing situations. As Tiltman recalled, Bertrand 

intuitively knew when he was about to be asked a question he 

could not answer for security reasons, and would always interrupt 

his interlocutor with the phrase “ne pas demandez,” “don’t ask.” 

21
Tiltman also liked to recall another anecdote related to his 

dealings with Bertrand. A couple of days after the beginning of 

the war, a German aircraft was shot down over Edinburgh, and a 

map containing the German Luftwaffe grid system for the North 

Sea was recovered. The map eventually found its way to Bletchley 

Park, and was hung on the office wall of the head of the Air Section, 

Josh Cooper. Tiltman pointed out that Cooper had a sensitive 

soul, and thought that the many ladies who had to enter his office 

and see the map would be bothered by the blood stains on it. He 

consulted with a staff member who was a pathologist by training 

to find a way to remove the stains without damaging the grid. A 

method was found, and during the cleansing, Cooper invoked the 

following from Macbeth:

Will all great Neptune’s ocean wash this blood

Clean from my hand? No; this my hand will rather

The multitudinous seas incarnadine,

Making the green one red. 

The map was henceforth christened “Lady Macbeth” (even 

though the invoked passage is by Macbeth himself, not his wife).

When, in May 1940, Bertrand finally introduced Tiltman to the 

area where the French worked on Enigma, Tiltman responded by 

presenting “Lady Macbeth” to his French colleague as a souvenir. 

He remembered spending about twenty minutes telling the story 

behind it, complete with the Macbeth quote only to find that the 

story lost everything in translation. The French never could be 

brought to see the humor in it. 

By mid-May 1940, only days after the Germans launched their 

offensive against the Netherlands, Belgium, and France, Bertrand 

was convinced that France was about to fall. He told Tiltman that, 

while France valued the party GC&CS had sent to France, the time 

had come to get them out. He further made a remarkable promise. 

Bertrand reassured his allies that nothing they had worked on 

together, particularly Enigma, would fall into German hands. 

Amazingly, that promise was kept, even though at least a hundred 

French officers knew about the work being done on Enigma. The 

22
Germans never became aware of the extent to which the French 

and the British had penetrated Enigma. Bertrand was able to 

keep to his commitment even though he himself was picked up 

by the Abwehr (German military intelligence) during the war and 

questioned.

One of Bertrand’s final acts before the French collapse fell into 

the category of lost opportunities. He handed to Tiltman, without 

explanation, a paper that contained a number of five-figure 

groups. The British, unaware of what it represented, filed it away. 

Only later, after much effort by both the British and the Americans 

to break into the system, did they realize that Bertrand had handed 

them the front page of the German diplomatic double-additive 

system known to the Allies as Floradora. One can only guess how 

much effort could have been spared had the British recognized 

what they were handed, or had Bertrand fully explained it to 

them.

In addition to his work coordinating efforts with the French, in 

March 1940 Tiltman was sent to Finland during the last two weeks 

of the Russo-Finnish War. He was not able to provide the Finns 

with much cryptologic help. His sole contribution was to tell them 

that the Soviet submarines operating in the Baltic were using onetime pads; hence, their messages were unbreakable as long as the 

system was used correctly, as it was. For his part, he received from 

the Finns a number of captured Soviet naval codebooks, copies of 

which would later be provided to the Americans.

Early War Work at Bletchley Park

Tiltman’s responsibilities at Bletchley Park became, and would 

remain throughout the war, varied. He claimed that he was never 

comfortable working with machine systems, and his experiences 

with the most famous German system, Enigma, were limited. This 

did not prevent him, as we shall see, from doing the extensive 

linguistic work that led to the British being able to break into a 

very sophisticated German cipher machine, the one the British 

called Tunny. He was, moreover, without equal in dealing with 

23
nonmachine, or hand, systems. Even before the war, he was 

recognized as the person to whom undiagnosed systems were 

handed for successful exploitation. And his successes, even on 

seemingly innocuous or unimportant systems, led to greater 

breakthroughs on the more glamorous ones, and to intelligence 

insights that proved not only valuable but chilling in the knowledge 

they provided.

For example, in 1939 and 1940 he was successful in breaking 

into a succession of field ciphers the German military was using for 

general weather forecasts. Other systems he worked on included 

those used by the German railway, and ones employed by the police 

and the SS (Schutzstaffel, the organ of the Nazi Party charged with, 

among other things, central security and the extermination of 

“undesirable elements” in society). The railway used a variant of 

the Enigma machine, but without some of the security devices 

built into the military and naval versions. The traffic derived from 

his break-in enabled the British to detect large troop movements 

to the east in 1941. This information formed part of the basis of the 

warnings British prime minister Churchill sent to the Soviets that 

they were about to be attacked. The Soviet leader, Joseph Stalin, 

chose to see in these warnings an imperialist-capitalist plot to 

draw him into a war with Germany, so he ignored them. Hundreds 

of thousands of Soviet troops paid the price for his ideologically 

driven blindness.

Insight into the SS and police systems enabled reporters to 

follow the matter-of-fact reports turned in on the results of actions 

to “cleanse” the areas in the east occupied by German troops as 

they rolled into the Soviet Union. They also read with increasing 

horror the precise reports of “discharges” from the numerous 

concentration camps established by the German killing machine. 

In one of the great incongruities of war, the section assigned to 

work this target had been set up in one of the rooms in the original 

mansion house at Bletchley Park, rather than the military huts 

built on the estate grounds to house the other elements at work. 

The room they were given had been a nursery. They read and 

24
tabulated the results of German implementation of the “Final 

Solution” in a room decorated with Peter Rabbit wallpaper.

Tiltman’s preference for working nonmachine ciphers in no 

way implies an inability to work on more sophisticated systems. In 

addition to his work on Enigma variants noted above, he was also 

responsible for the initial breakthroughs against another German 

high-level machine. The German high command, that is, Adolf 

Hitler and his generals, employed teleprinter to communicate 

amongst themselves with messages enciphered using principally 

the Lorenz SZ40 cipher machine. The British came to refer to 

this system as Tunny. Once it was understood how Tunny was 

used, and by whom, it was recognized that the contents of these 

messages would provide a “grand strategy” complement to the 

knowledge contained in Enigma enciphered messages. As an 

undiagnosed system, the initial attack on Tunny became Tiltman’s 

responsibility, though at this stage the full import of the system 

was not appreciated (and would not be until Tiltman’s abilities 

allowed messages sent on the system to be read). By 1941 he 

had identified the encipherment system used (a binary additive 

system) and made the initial break-in, which led to what was to 

become a hugely valuable and productive cryptanalytic industry in 

GC&CS, on a par with the Enigma work.

The weakness of Tunny was caused by operator laziness. 

Having demonstrated that the normal international five-unit 

teleprinter coding was used, Tiltman next established the additive 

nature of the key from the short introductory depths (two separate 

messages sent using the same machine settings, as not infrequently 

happened when the machine was first introduced in 1941). If 

he added such messages together, the result was the intermixed 

stream of the two plaintexts. Operators usually recognized their 

error and stopped such depths after at most a few dozen letters. In 

late August 1941, however, a German operator sent a long message 

and was then asked to repeat it. In an amazing mistake, he did this 

using the same cipher settings but retyped the whole message. 

Within a few characters from the start his second transmission 

(with varying abbreviations and errors) diverged from his first, 

25
producing not only a long depth but one with basically the same 

underlying plaintext in both parts. 

The two transmissions still contained various garbles, and 

the recovery of the plaintexts (and hence the corresponding key) 

took Tiltman some time. Thereafter his Research Section, and 

particularly William Tutte, who made the first break-in, solved 

the Lorenz machine early in 1942. Machine setups were different 

on different links, and the various elements of the machine (it 

involved twelve pinwheels with a total of 501 pins, and various 

later complications) were changed with ever-increasing frequency. 

By 1943 GC&CS realized that large-scale mechanization was both 

necessary and feasible, which led to the first practical application 

of a large-scale program-controlled computer named Colossus to 

exploit it. By the end of the war, ten of these machines were in 

use.

Something of the intellectual accomplishment breaking into 

the Tunny system represented (and Tiltman’s self-effacing wit) 

can be seen by an anecdote Tiltman recalled years after the war. 

Shortly after the end of the conflict, two Tunny machines captured 

from Field Marshal Kesselring’s (the commander of German 

forces in Italy) train arrived at Bletchley, and Tiltman was asked 

to explain how he had broken into the system in the first place. 

He replied that he was able to use the twelve-letter indicator of 

each message. When it was pointed out to him that the captured 

machines had no letters on them, he replied, “I can’t help that, this 

is the first time I’ve seen it too.” 

Ironically, shortly after the August 1941 messages were sent, 

the Germans made improvements to their use of the system, and 

never again was key from depths resolvable on a sufficient scale to 

have recovered the whole machine. Without those two messages, 

and Tiltman’s adept exploitation of them, the British would not 

have been able to break into Tunny. To gain some idea of the value 

of his breakthrough, in March 1945 alone Tunny transmissions 

totaling some five million characters, containing intelligence of 

critical importance, were deciphered. As an additional indication 

26
of the importance GC&CS placed on Tunny exploitation, by 1944 

some 500 people were involved in cryptanalytic efforts against this 

system, with another 600 involved in intercept and processing of 

Tunny traffic. 

Tiltman would later point to the exploitation of Tunny as a case 

of pure cryptanalytic work. GC&CS regularly received captured (or 

stolen) codebooks or cipher keys on other systems, but for Tunny 

none was ever forthcoming. He pointed to GC&CS success here 

to counter postwar claims that cryptographic systems were not 

broken by pure cryptanalytic effort, but always relied on captured 

machines, codebooks, or cipher keys.

Work Habits/Personality

By this time Tiltman had developed his work habits as well as 

certain axioms that framed his efforts through the war and beyond. 

He found that most of his useful thinking went on at a level just 

below full consciousness. Success came when he was able to so 

immerse himself in a system that the solution would be formulated 

quite subconsciously. Because of that, he preferred to do his 

own preliminary analysis, registration, and indexing, disdaining 

the use of machines except for simple sorting and listing. A true 

indication of his genius was that he relied on intuition born of 

experience to tell when a tenuous lead had played out and needed 

to be abandoned. Since he firmly believed that cryptanalysis in the 

diagnostic stage was more an art than a science, he warned against 

fear of making mistakes (remember that he was amused with, 

not embarrassed by, his Chinese Telegraphic Code experience). 

Paths that turned out to be blind were learning experiences, not 

failures.

He had a clear understanding of his own limitations. He admitted 

to having no knowledge of higher mathematics (something not 

considered a drawback in prewar Britain--most of the cryptanalysts 

hired before the war were anything but mathematicians), and 

claimed only an instinctive grasp of probability theory. In addition, 

as we have seen earlier, he denied being a linguist, though he would 

27
eventually break codes and ciphers in over a dozen languages 

(languages whose roots varied from Indo-European to Asiatic 

to Semitic). He insisted, however, that a research cryptanalyst 

needed a working knowledge of comparative linguistics and an ear 

for the sound patterns of unfamiliar languages. And, as we have 

also seen, he placed great stock on cryptanalysts gaining a general 

working knowledge of the other branches of SIGINT, much as he 

had done while serving at Simla.

One of the peculiarities about Tiltman noticed by his associates 

was that he never worked sitting down. Rather, he had a desk 

specially constructed that allowed him to stand while puzzling 

over the latest cipher system to come to his attention. He also 

demonstrated a singular ability to concentrate on the problem at 

hand, and then to essentially forget all about it once he had done 

his part and had moved on to another issue. One of his wartime 

colleagues remembered in particular passing him a system which 

had stumped several analysts for a number of weeks. Tiltman 

unraveled it in two days. When approached a few weeks later and 

updated on further progress made against it, he had completely 

forgotten about it and had to be reminded of the salient points.

He surprised many with his lack of concern for the mundane 

protocols of military life, this in spite of the fact that he remained, 

throughout his life, most military in bearing himself. Upon being 

recalled to active service in 1939, he readily admitted that he 

could no longer remember whether his insignia of rank should be 

mounted above or below the crown on his uniform. He repeatedly 

drove his adjutant at Bletchley Park, a major consumed with 

enforcing proper military bearing and decorum, to distraction 

with his informal practices such as granting weekend passes 

to subordinates who merely knocked on his door and asked, 

bypassing the adjutant completely. 

Tiltman rarely wore his own uniform, and instituted changes 

in the uniforms of others. For instance, when William Filby (later 

a renowned cryptanalyst in his own right, but at the time a newly 

minted private) first reported for duty in 1940, he marched up to 

28
Tiltman’s desk, halted in the time-honored fashion of the British 

army with a vigorous stomp of his boots, and saluted. Tiltman 

looked at Filby’s feet, and exclaimed, “I say, old boy, need you 

wear those things?” referring to Filby’s army issue boots. From 

that day forward, Filby added white sneakers to his regulation 

uniform. Needless to say, the shoes, plus Tiltman’s incurable habit 

of referring to an enlisted subordinate as “old boy,” did nothing to 

endear him to military perfectionists.

In another example, Tiltman, as a senior officer, had to deal 

with his own chauffeur who had “borrowed” Tiltman’s official 

vehicle for a tryst with his girlfriend, and then had the misfortune 

of crashing the vehicle. Tiltman’s inclination to deal with the 

matter quietly and personally had to give way to military propriety, 

and he was forced to convene and preside over a court-martial, 

his first. Again, he frustrated his adjutant, and provided mirth for 

everyone else involved, by constantly asking the major what he 

was supposed to do next during the proceedings, and by asking the 

accused if what was happening met with his approval.

He showed his human side in many other ways throughout 

the war. He intervened personally when necessary to make sure 

members of his section were paid properly and on time. He went 

so far as to get money advanced to individuals when the army pay 

system broke down, as it is wont to do in the British Army as in any 

other. On another occasion, he took the time to intervene directly 

to make sure that promises made to commission graduates of 

his Japanese training course when they went to India were kept. 

The time taken out of his hectic schedule to follow-up until the 

commissions were all granted he considered a small price to pay 

to ensure proper treatment of his people. 

His willingness to be flexible in the matter of uniform use did 

not stem from any disdain for military practices. Instead, it was an 

acknowledgement that the war had caused a truly odd assortment 

of individuals to be called to the colors and assembled at Bletchley 

Park. He never lost sight of the goal, which was to gather the best 

minds available to break Axis ciphers. All other matters were 

29
secondary, and should not be allowed to get in the way of getting 

the job done.

That the people doing the job, or being prepared to do the 

job, were of the utmost importance to him was clearly shown 

by the emphasis he placed on ensuring proper training which 

extended, as noted, to both language preparation and making 

sure that each new cryptanalyst received a firm grounding in the 

business they were now about. His involvement did not end with 

the establishment of the schools to provide the necessary training. 

He would often take time from a frenetic wartime schedule to visit 

the classes and talk to the students to inquire about their progress. 

His ability to impart his skills to the young and to inspire their 

enthusiasm and success continued until he was in his eighties. He 

is said to have made the difficult appear easy and the seemingly 

impossible seem a worthwhile challenge.

30
Initial Relations with the U.S.

Interestingly enough, it was most likely precisely Tiltman’s 

ability to put formalistic trappings aside that enabled him to 

make his greatest contribution not only to the war effort, but to 

the postwar cryptologic world as well, the cementing of relations 

between the United States and Great Britain in the arena of signals 

intelligence and communications security. The Americans saw 

him as the embodiment of British eccentric brilliance, a perceived 

stereotype the Americans have always found endearing. At the 

same time, he avoided the perception of falling into the negative 

American stereotype of the British, that of officious condescension. 

He reciprocated their warm acceptance, and added a toleration 

of U.S. habits not generally found among his colleagues. A truly 

close personal and official relationship blossomed essentially from 

initial contact.

That first encounter came even before U.S. entry into the 

war. As early as 1940, British prime minister Winston Churchill 

recognized that U.S. entry into the war on the side of Britain was 

essential to success, and instructed his naval and military forces, 

and his intelligence services, to prepare for full cooperation 

with their American counterparts. These instructions perfectly 

complemented the thinking of U.S. president Franklin Roosevelt, 

who also understood that only by the U.S. standing together with 

Britain could German and Japanese aggression be defeated. 

With this atmosphere set at the highest levels, exchanges of 

visits at a variety of levels dealing with numerous topics began. On 

the SIGINT side, a four-person American delegation (consisting 

of Major Abraham Sinkov and Captain Leo Rosen for the Army, 

and Lieutenants Robert Weeks and Prescott Currier for the Navy) 

visited Bletchley Park in early 1941. The four traveled to Britain 

aboard the British battleship HMS King George V escorting a 

beef convoy that had originated in South America and then to the 

naval base at Scapa Flow, Scotland, and hence by cruiser, HMS 

Neptune, to England. They carried with them information on U.S. 

31
cryptologic work against the Japanese, to include an analog of the 

Japanese diplomatic machine the Americans called Purple. 

The trip, especially the final leg, was not without incident. 

The original plan called for the group to be met at Scapa Flow by 

a representative from the U.S. embassy with two flying boats to 

transport them and their equipment to the south of England. They 

had, however, brought some thirty crates of material weighing up 

to two tons. Some of the crates were too large to fit through the 

hatch of the flying boats, so that option could not be used. The 

captain of HMS King George V then arranged with an acquaintance 

who commanded HMS Neptune to give the Americans a ride 

south. While in the Channel, the ship was spotted by German 

aerial reconnaissance and attacked by two German dive-bombers. 

While none of the personnel on board were wounded, the crates 

of equipment, tied down on deck, were all hit by machine gun 

fire as the bombers strafed the ship. At this point the luck of war 

intervened, and the would-be Allies benefited from the fact that 

the Germans had chosen to ignore the provisions of the Geneva 

Convention on armaments by using explosive rounds in their 

machine guns. As a result, the rounds exploded on contact with the 

crates rather than penetrating them. The equipment the Americans 

were bringing to demonstrate to the British escaped damage. 

The British, especially Tiltman, were impressed by the 

willingness of the Americans to share their most sensitive 

cryptologic successes. In particular, Tiltman thought that in 

turning over the Purple analog the Americans had made what 

he called “a magnificent gesture,” one that bound the British to 

in turn share their closely held successes against the German 

Enigma machine. Tiltman ran into no opposition in turning over 

what he knew about Japanese military systems, most of which was 

new to the Americans, who had been concentrating on Japanese 

diplomatic and naval systems.

His superiors, particularly A. G. Denniston, were caught off 

guard by the openness of their soon-to-be allies, and there appears 

to have been considerable debate about what full disclosure 

32
meant. They especially wanted to withhold information on the 

successes Britain had achieved in tackling the Enigma machine. 

They had concerns about American security practices (which, 

given the notorious weakness of U.S. codes and ciphers up to this 

time, were not unwarranted), and feared that the Americans would 

inadvertently reveal information that the Germans could use to 

identify and correct their own cryptologic vulnerabilities. Since 

Britain was dependent on continued success against the naval 

Enigma in particular for survival, they did not think their concerns 

were unreasonable.

British sensitivities about the security of Enigma ran deep, and 

extended throughout those in the know in British governmental 

and military establishments. When the first successes against 

the system had been achieved, attempts were made to disguise 

the source by attributing all the intelligence to a spy codenamed 

Boniface, but that fiction soon wore thin. What the Boniface myth 

gave them, as Tiltman later described it, was a system that divided 

recipients of the material into three groups. The first set was fully 

in the know. The second was not, and its members were “too 

dumb” to figure out the truth. As a result, their distrust of material 

provided by spies led them to disregard the intelligence altogether. 

The third group was potentially the most dangerous. Its members 

were not in the know, but had figured it out. Since they had not 

been briefed, no restrictions were placed on whatever speculation 

they chose to indulge in. They did, however, accept the intelligence 

and used it to great effect. Given that the British had devised this 

elaborate scheme for handling Enigma material within their own 

ranks, their reluctance to be forthcoming with the Americans 

becomes more understandable. 

Tiltman, perhaps in small part because he was not as attached 

to the Enigma problem, but very largely due to his judgment 

of what was at stake, took a broader view of the issue. Given 

American openness with Purple, he believed that British reticence 

over Enigma would be nothing but a cause for future trouble 

since it made a mockery of the entire concept of full exchange of 

information. He argued that the American delegation could not 

33
help but notice that they were being denied access to large sections 

of Bletchley Park. They would inevitably draw conclusions from 

that fact, which would not be in the best interests of furthering 

relations between themselves and GC&CS.

He took his case over Denniston’s head to Sir Stewart Menzies, 

“C,” who as well as being head of the British Secret Intelligence 

Service (SIS, popularly known as “MI 6”) was also administratively 

responsible for GC&CS. After considerable discussion, Menzies 

conceded that sharing was necessary, but insisted on stringent 

preconditions. The American delegation would have to provide 

the British with a list of the names of individuals they intended to 

share the information with, and agree to not add anyone to the list 

without prior British permission. And this agreement was to be 

made in writing before even the scope of the British Enigma effort 

was revealed to them. It was very much the cryptologic equivalent 

of buying a pig in a poke. 

The Americans, junior officers all, not unnaturally balked at the 

very thought of signing such a commitment, no doubt envisioning 

the repercussions that would follow when they returned home. 

They saw in the preconditions the very embodiment of the officious 

condescension Americans had almost by instinct historically 

associated with the British. Their fury was probably exceeded only 

by the degree to which the responsibility they were being asked 

to assume appalled them. Tiltman again used all his powers of 

persuasion, this time with the Americans, to convince them, sight 

unseen, that the prize was worth the game, and they finally signed. 

His success laid the foundation for unparalleled cooperation that 

continues to this day. The preconditions, and continued British 

reticence with regards to Enigma, left bad feelings that Tiltman 

continued to have to deal with.

The cryptologic services of the soon-to-be allies continued to 

cement their budding relationship in the fall of 1941. In September 

Tiltman worked with Denniston to arrange for Geoffrey Stevens, 

one of the men he had trained and sent to Hong Kong (the unit 

he served with had since been moved to Singapore), to be posted 

34
to Washington. Stevens became the first regular liaison between 

GC&CS and its American counterparts.

With the entry of the U.S. into the war in December 1941, 

cooperation between the cryptologic services of the two countries 

deepened. By spring 1942, it was the turn of the British to cross 

the Atlantic, and who better to represent GC&CS than the one 

individual who had almost single-handedly saved the nascent 

relationship in 1941. Tiltman boarded a U.S. warship, laden with 

eight heavy mailbags filled with reports and technical information 

from Bletchley Park. The crossing was not without its moments of 

levity, at least in retrospect. He recalled later that his instructions 

were to keep the bags in his cabin at all times (given the size of 

accommodations on warships, that alone must have presented 

some degree of discomfort), but he was to move them to the side 

of the ship for removal or sinking in case of emergency. Since 

he was barely able to lift even one of the bags, he had to prevail 

on the good graces of his hosts to let him know in advance when 

drills would be held (so he would not have to move the material 

needlessly), and to detail a party of seamen to assist in moving the 

bags in the event of a real emergency. Fortunately, none arose.

During the voyage he was made party to what amounted to 

a breach of security by the communications officer of the ship. 

Knowing something of Tiltman’s mission (the officer handled 

enciphered messages), he took it upon himself to show Tiltman 

the secure communications gear he was responsible for. Tiltman 

promised himself to cover the officer’s well-intentioned indiscretion 

by acting as if he had never seen the gear when he would be 

shown it officially. Upon his arrival in the U.S., both the Navy (in 

the person of Joseph Wenger) and the Army (through William 

Friedman) demonstrated the gear for him, each independently 

of the other. As it turned out, Wenger had received authorization 

for his actions. Friedman, much like the naval officer aboard ship, 

discussed the equipment on his own authority. This, according to 

Tiltman, led to a confrontation between Friedman and General 

Strong, the staff intelligence officer (G-2) for General Marshall, 

which may have led to one of Friedman’s breakdowns.

35
The material and expertise that Tiltman brought with him 

would prove to be invaluable to the Americans. Included were Vichy 

French colonial codebooks complete with cryptanalytic notes and 

comments by GC&CS’s French section, microfilms of materials 

related to British efforts to exploit the German diplomatic Floradora 

system, and information from the GC&CS Research Section (which 

Tiltman had set up) on the methods they used to solve several 

complex ciphers. The methods involved were unknown to the 

Americans, who quickly put these new insights to work.

Tiltman’s instructions for his visit (which lasted a month from 

late March to late April 1942) included working out a full interchange 

of information with the U.S. cryptologic efforts, and to see if he could 

do anything to encourage the Army and Navy to be more cooperative 

amongst themselves. He quickly realized that trying to insert himself 

into the peculiar tribal rituals which made up Army-Navy relations 

would only be counterproductive, and he backed away, ignoring 

that part of his instructions. He was also to try to effect GC&CS’s 

desired division of effort with the Americans whereby the U.S. would 

concentrate its efforts against Japanese systems, leaving German 

and Italian ones to the UK. Enigma continued to be a bête-noire, 

with many in the upper reaches of GC&CS (particularly Commander 

Travis, who had just effectively replaced Denniston as head of 

GC&CS) still reluctant to fully share technical information with 

the U.S. Travis was especially loath to have the Americans spend 

resources duplicating the British effort. 

For his part, Tiltman was impressed by the efforts being made in 

the Navy’s OP-20-G office against Japanese naval systems, especially 

JN-25. He professed to being staggered by the number of tabulating 

machines in use (remember, his preference was still, and would 

remain throughout his career, to work by hand). He was not totally 

won over to this “automated” way of attacking cipher systems.

The U.S. was willing to accept that part of the proposed division 

of effort which pertained to Japanese systems. The Army’s Signals 

Intelligence Service (predecessor of the Army Security Agency, which 

was later to become part of the Intelligence and Security Command 

36
(INSCOM)) in particular was reluctant to develop a formal working 

agreement, but tight resources created such an arrangement by 

default. Tiltman had been authorized to limit U.S. access to traffic 

and cryptanalytic material should such a step prove necessary. He 

recognized innately that any attempt at such heavy-handed tactics 

would produce results the opposite of those desired, so he wisely 

held his hand in this matter. 

Where the Americans had considerable difficulty accepting the 

British proposal came with Enigma, particularly the system used 

by U-boats which had converted to a four-wheel machine on 1 

February 1942 and which the British, at the time, could not read. 

With U.S. merchant shipping losses in the North Atlantic and along 

the U.S. coast mounting, it was difficult for the U.S. Navy to accept 

the British position that they were best equipped to deal with the 

problem on their own. The U.S. wanted a copy of the British bombe 

(the machine being used to break into Enigma keys based on cribs), 

and they wanted to develop their own versions of that machine. To 

make any such effort worthwhile, however, they would be dependent 

on receiving German intercepted traffic from the British since the 

U.S., at the time, had precious little in the way of collection resources 

in the European theater of operations.

The American officer who put considerable pressure on the 

British was Rear Admiral Joseph Redman, director of naval 

communications, and he singled Tiltman out for attack. Tiltman 

again used all his persuasive powers to break down the reluctance 

of his boss, this time Commander Travis. By mid-May 1942, he 

had succeeded to the point where GC&CS was willing to admit 

to the Americans the reasons for its difficulties in dealing with 

the four-wheel Enigma. A further concession was an agreement 

to allow the Americans to study the British bombe, and Travis 

promised to provide one at, the Americans understood, the earliest 

possible moment (which, given the few machines in existence, 

and the need for all of them to be operational, did not promise to 

be in the immediate future, especially since Travis intended the 

timeframe to be August-September). Because of that, and the 

natural misunderstandings that arose out of varied interpretations 

37
of “earliest possible moment,” Enigma continued to plague U.S.-UK 

relations. 

Tiltman himself was not immune to the problems the Enigma 

matter caused. In fact, it was responsible for some of the more 

unpleasant incidents of his visit. We have already seen that Admiral 

Redman zeroed in on him. In addition, he had asked at one point for 

a meeting with Agnes Driscoll, the formidable Navy cryptanalyst, to 

hear her ideas about Enigma. He went unsuspecting to the meeting, 

which turned out to be on the stage of an auditorium in front of an 

audience of technical experts from both services. He recalled that 

this included Friedman, Rowlett, Sinkov, Kullback, and the heads 

of both the Army and Navy cryptologic services. Mrs. Driscoll then 

proceeded to grill him on the British effort against Enigma, a subject 

he willingly admitted he was ill equipped to deal with, given that he 

had barely ever worked on the machine. She was convinced that the 

British were making more to-do about the solution to Enigma than 

was necessary, and she claimed to be able to do the job properly. 

She believed, however, that the British were withholding a vital 

piece of information, and that their refusal to share it was all that 

was thwarting the U.S. effort. She was wrong on both counts, but 

Tiltman was in no position to argue the point because of his technical 

ignorance of the subject. Decades later he still ruefully remembered 

the experience.

The visit to the U.S. had a lighter side as well. During a meeting 

with Friedman, while the latter was going over some of the reports 

that Tiltman had brought with him from GC&CS, he looked up from 

his reading and asked what a “finnery” was. Tiltman indicated that 

he did not know for sure, but believed it must refer to a practice the 

Finns had of changing the key settings on their Hagelin machines 

in mid-message. Friedman was satisfied with this, and began using 

the term as part of his cryptologic jargon. The punch line came only 

after Tiltman returned to Bletchley Park. He called in his assistant 

and asked why he had not been briefed on “finnery.” The assistant 

had to somewhat sheepishly explain that there was no such thing. 

The term had gotten into a message as a result of a cryptographic 

bust and had not been caught in the editing process. 

38
All in all, the trip was a success. Enigma, however, remained a 

sticking point (and Tiltman’s relationship with Admiral Redman 

was destined to get worse), and would continue to cause problems, 

as we shall see. He could not prevent efforts by the Americans to 

begin building their own bombes, especially to deal with the fourrotor machine introduced by the German submarine service, an area 

where the version developed by the U.S. Navy would prove superior 

to the British ones. But that was essentially the only major point of 

contention between the new allies. Agreement was reached on the 

U.S. taking primacy in dealing with Japanese systems. Tiltman made 

arrangements for British intercept of Japanese communications to 

be routed to Washington for American processing. He also made 

arrangements for the Navy to send two or three officers to GC&CS 

to study how the British had set up research groups so that the naval 

effort to set up similar groups would not have to relearn lessons the 

British had mastered. 

The naval officers were but the vanguard of a much larger 

American contingent. By the summer of 1942 the first of what were 

to be over 100 U.S. Army personnel arrived at Bletchley, eventually 

headed by William Bundy, the future foreign policy advisor to both 

Presidents Kennedy and Johnson and coauthor of the Tonkin Gulf 

Resolution. Tiltman considered this one of the noblest gestures 

of the war, and readily admitted that the influx of American 

manpower, here as in other aspects of the joint endeavor, made a 

critical difference. The flow of personnel the other way was not as 

great, necessarily so given the relative numbers involved. Tiltman’s 

contribution from the British perspective was to make sure that the 

British contingent to the U.S. remained a unit under British control. 

Commander Travis had been inclined to turn complete control 

over to the Americans, but Tiltman intervened, arguing that this 

would risk fragmenting the British contingent and dissipating its 

influence. 

In addition to building relationships with the Americans, 

Tiltman also used this visit (as he would use each visit to this side 

of the “pond”) to strengthen cryptanalytic relations with Canada. 

He retained interesting memories of Canada. He noted that there 

39
always seemed to be a layer of bureaucracy missing in the way 

Canadians handled things. As he put it, you would run into an 

obscure Signals officer who would just happen to have a close friend 

who just happened to be chief of the general staff, and neither of the 

friends would see anything wrong with using that connection to get 

things done. The lack of the red tape more commonly associated 

with both the British and Americans was refreshing.

Tiltman returned to Britain, but not uneventfully. He flew back 

in an unheated Liberator bomber that developed problems as it 

approached Scotland and had to execute a crash landing at Prestwick 

airport at full speed with flaps down in an attempt, successful as it 

turned out, to bring the plane to a safe stop. He had cemented the 

high regard Americans held him in by bringing them codebooks, 

cipher tables, and the benefit of his own professional observations 

on a range of cryptanalytic problems. That he returned essentially 

empty-handed was a suggestion of the true state of the relationship 

between the allies in the first half of 1942. The UK was still well out 

in front of the U.S., and the British had to content themselves with 

intangible contributions from the Americans that came in the form 

of discussions, observations, and insights.

COMSEC Efforts

Back at Bletchley, nonliaison tasks awaited Tiltman’s attention. 

Before his trip to the U.S., he had been named to replace “Dilly” 

Knox as GC&CS Chief Cryptographer. Interestingly, Tiltman always 

recollected that he had replaced Oliver Strachey in this role. Strachey 

had, in fact, been replaced by Knox in 1939, with Tiltman replacing 

Knox in 1942. Tiltman and Knox never got on with each other, so it 

may not be surprising that this should prove to one of the rare times 

when Tiltman’s memory betrayed him. On numerous occasions 

he admitted that he never understood how Knox had achieved the 

reputation that he had. Tiltman’s recollections of his dealings with 

Knox mostly involved the end of Knox’s career, at a time when he 

was terminally ill, so that may account for his less than favorable 

opinion. Tiltman also acknowledged that, at one of his first meetings 

with Knox, he committed the tactless and (for a cryptanalyst) 

40
unforgivable sin of reading a stretch of key Knox had recovered 

over his shoulder and rendering it into English. This ranks right up 

among the social graces alongside of someone who looks over your 

shoulder while you are completing a crossword puzzle and provides 

you with the answers before you have time to fill them in yourself.

Tiltman would later claim that the title of Chief Cryptographer 

was largely an honorary one, meaning he received no extra 

compensation for it. In fact he was amused to learn after the war 

from a captured German that his foes thought that the British Chief 

Cryptographer was paid more than the Archbishop of Canterbury. 

In reality the position carried several tangible responsibilities. His 

duties included taking over or giving advice on the attack on any 

undiagnosed or unexploited system, a role he had been filling in any 

case given his reputation for dealing with such systems. A second 

part of the job was to oversee the development of secure British 

ciphers. For this later task he was given a twelve-man staff, and with 

those limited resources he was expected to advise on the technical 

security of military, naval, diplomatic, and other cipher systems. He 

estimated that he spent about one-fifth of his time during the war 

designing cipher systems to replace ones which had been shown to 

be inadequate for the conditions under which they had to be used.

His most significant personal contribution to this effort eventually 

(from late 1943) helped to secure British naval communications for 

the rest of the war. The cipher system the Royal Navy had been using 

had become vulnerable both because of German skill in attacking it, 

and because it was being overused. Britain had developed a very good 

rotor machine called Typex (a variant of the commercial Enigma 

machine), but could never produce enough of them to service all the 

users who had to have secure communications. This left the British 

dependent on hand-made systems which, by nature, were subject 

to overuse. While all branches of the British armed forces faced this 

problem, it was especially critical for the Royal Navy. Its system was 

used by the American, British, and Canadian navies up to mid-1943; 

1,700 holders, all of whom had to be in a position to communicate 

securely, were dependent on what was a vulnerable system. The 

fact that three allied navies needed to communicate jointly only 

41
compounded the problem of overuse and the criticality of coming 

up with a solution. 

Tiltman replaced it with a system he designed. The refinement 

he introduced consisted of a plastic grille which contained 100 fourdigit-wide windows randomly spaced. This was superimposed over 

an additive sheet that had forty-eight lines of sixty-eight digits each. 

Setting squares for the placement of the grille provided 100 possible 

settings, and a conversion table appeared on each sheet with mixed 

sequences of digits from 00 to 99 for indicating purposes. Each 

sheet was used for one day only. The placement of the grille was 

determined through a substitution pattern sent to each user. This 

fulfilled one of Tiltman’s basic prerequisites for the security of any 

cipher system. Security had to be taken entirely out of the hands of 

the users; otherwise, they would create shortcuts that would destroy 

any semblance of protection.

Known as the Stencil Subtractor Frame (S.S. Frame or SSF), it 

was put into fleet-wide use in December 1943. Combined with the 

introduction of a new codebook in June 1943, it fixed the problems 

the Royal Navy had been experiencing, and German ability to exploit 

its communications ceased effectively from June. Their recoveries of 

the new codebook were ended by the introduction of the SSF. They 

were able, through an impressive piece of cryptanalytic research, to 

diagnose how the SSF worked through attacking a month’s worth 

of auxiliary ship traffic and by throwing large numbers of analysts 

against the problem, but this diagnostic success only served to 

convince them that they would be unable to exploit the system. The 

Germans had used their ability to read the British naval system to 

great effect in attacking convoys coming from America and Canada. 

That effectiveness had already begun to disappear by May 1943 

when improved convoy methods forced the Germans to withdraw 

their submarines from the North Atlantic. The introduction of new 

codebooks, first in June 1943, then, as we have seen, in conjunction 

with the S.S. Frame in late 1943, put paid to any thoughts the 

Germans might have entertained of regaining that advantage. 

While Tiltman’s contribution was by no means the sole, or even the 

principal, cause for the German defeat, it certainly played a role. The 

42
British government recognized the value of his effort by awarding 

him 1,000 pounds in 1944 for the invention of this cipher device, 

orders for which had by then reached over 17,000.

A second system introduced by Tiltman enjoyed less success, 

at least as far as the Allies were concerned. This was the Cysquare, 

loosely based on a grille system he had developed while serving 

in India in the 1920s. As mentioned earlier, he had believed that 

system to be secure, but his own subsequent study of it showed him 

its weaknesses, which he promptly remedied. He had also worked 

on improving it throughout the 1930s, a period when his activities 

were actually frowned on since it was thought that cryptanalysts 

should not waste their time developing ciphers or ciphering systems. 

Faced with the need for a low-echelon cipher system, he developed 

Cysquare for use by the British Eighth Army in North Africa. It was a 

resounding failure. Operators soon found out that desert conditions 

made it impossible to distinguish between the cells they were 

supposed to use and the ones that were “grayed” out. They rapidly 

abandoned it for other methods. 

Interestingly, Tiltman’s system was not dismissed as readily 

by his enemies. The Germans captured a number of the stencils 

during the North African campaign and thought the concept had 

considerable merit. They modified it and used it as one source (there 

were others, to be sure) to create their own field cipher, known as 

Rasterschlüssel, which came into wide use in October 1944. Tiltman 

noted ruefully that the British had considerable trouble with this 

system. He believed they would not have been able to break into 

it had the Germans not made mistakes while producing the pads 

required for its use.

Japanese Attaché System

In 1942 Tiltman once again took up his efforts against Japanese 

systems, this time turning his attention to the cipher used by 

the Japanese military attachés. The problem had originally been 

assigned to a number of French cryptanalysts who had managed 

to escape after the collapse of the French Army in 1940, and were 

43
now working at Bletchley Park. By early 1942, Tiltman was not at all 

pleased with the progress (or lack thereof) the French were making, 

and he opted to take over the effort personally. He soon found that 

the French had completely misdiagnosed the cipher, believing it to 

be a combined substitution and transposition system.

Tiltman quickly corrected the misdiagnosis, and discovered that 

he was dealing with a digraph code in which there were digraphs 

for basic kana symbols and for words and phrases commonly used 

in military communications. The two-letter groups were then set in 

a square grid in adjacent squares in either a horizontal or diagonal 

pattern and read vertically to form the encoded text. This was then 

enciphered using a “literal additive,” adding letters rather than 

numbers. 

As is often the case, Tiltman’s exploitation of the system was 

aided by mistakes by Japanese code clerks and by the stereotyped 

nature of the communications he was dealing with. The code clerks 

helped by making the classic mistake code clerks have made for as 

long as there have been code clerks. They kept reusing portions of the 

additive table (often out of sheer necessity, they had more messages 

to send than their keying system would support), providing their 

enemies with depth. The attachés themselves provided assistance 

as well through their formalistic phraseology. Each message began 

with the pat phrase “I have the honor to report to your excellency 

that . . .” With that generous crib as an aid, Tiltman was soon able to 

strip away the mystery of the system, baring the secrets contained 

within it.

To exploit that crib, however, Tiltman had to rely on a lesson 

he had learned in the 1930s about Japanese methods of encrypting 

their messages. In an attempt to foil attempts to exploit stereotypical 

beginnings, the Japanese used bisection. That is, they broke their 

messages into sections (sometimes as many as four), and then 

rearranged the order of the sections so that the beginning would fall 

in the middle of the transmitted text. Tiltman had learned early on 

to look in the interior of a Japanese message for stereotypical giveaways.

44
The secrets revealed by Tiltman’s breakthrough proved themselves to be well worth the effort put into breaking the cipher. 

Throughout 1943 and 1944, the Japanese diplomatic mission in 

Berlin was made privy to German planning for confronting the longanticipated Allied invasion of France. This included tours of and 

detailed briefings on the beach defenses the Germans were preparing, as well as insight into where the Germans expected the blow to 

fall. The Japanese attaché prepared meticulous reports containing 

this information for Tokyo, reports that were read in Washington 

and London with, one might expect, far more interest and concern 

for detail than they received from their intended recipients. They 

reinforced similar messages sent by the Japanese ambassador to 

Berlin, messages that were also read by the Allies thanks to the ability to read the Japanese diplomatic cipher system known as Purple.

Together, these two sources of information (combined with 

material exploited from Tunny) helped the Western Allies to prepare 

countermeasures for the beach defenses put in place by the Germans. 

More importantly, they reassured the Allies that the German high 

command expected that the main invasion would occur at the 

Pas de Calais, the narrowest part of the English Channel, and the 

point that would place the invaders closest to Germany’s industrial 

heartland in the Ruhr Valley. The Allies learned that the Germans 

expected a landing attempt in Normandy, but believed it would be 

only a diversion. Allied masters of deception put their best efforts 

into reinforcing the German preference for a landing at the Pas de 

Calais. They were gratified to see their efforts paying off through 

their continued insight into the reports from the Japanese attaché 

and ambassador. 

Having done the hard part, Tiltman set up a small subsection 

at Bletchley as part of his Military Section to handle continued 

exploitation of the attaché cipher. The subsection consisted of a 

team to handle the code and cipher breaking, plus a team to analyze 

the results. Tiltman had the added satisfaction of manning the 

subsection with graduates of the Japanese course he had established 

at Bedford at the beginning of the war with Japan, the effort the 

language “experts” had told him was doomed to failure.

45
Back to the U.S./The Turing Incident

By late 1942, Tiltman was on his way back to the United States 

for another series of meetings. This visit would call forth every bit 

of ally-building skills he had to overcome a wealth of contentious 

issues, most centering on continued mistrust over Enigma. The 

announced purpose of the visit was to work out the details of field 

cryptographic systems to be used in joint operations. It soon turned 

to issues of more import to the future well-being of the cryptologic 

allies.

Tiltman arrived back in the U.S. in December 1942, heading a 

three-man team. As noted, their brief was to help implement an 

agreement that would allow the two countries to jointly grade their 

own codes and ciphers on the basis of the level of security that was 

needed in a given situation and that could be expected from a given 

system. This would, hopefully, lay the groundwork for deciding 

which systems could be used in joint operations where rapid 

accessibility to each other’s communications could be vital. 

At issue was that the British were, as we have seen, by and large 

dependent on hand systems at a tactical level. The Americans, on 

the other hand, had adopted the Hagelin C-38 (M-209), and wanted 

the British to accept that system as well. The British believed that 

to replace their systems with the M-209 would involve more than 

getting the new materials to everyone who needed them. This 

was a monumental task in its own right given that British forces, 

like their American counterparts, were deployed across the globe. 

It would also involve a Herculean effort to retrain British code 

clerks, and this in the middle of a war. In addition, the British had 

legitimate concerns about the security provided by the M-209. It 

was particularly vulnerable when overused, as it often was in the 

heat of combat, and both the Germans and the Japanese would 

prove capable of exploiting it.

As Tiltman had anticipated, the initial meetings on this subject 

did not go smoothly. His task was rendered more difficult because 

one member of the British delegation (from the Royal Air Force) 

adopted a confrontational attitude, even though his marching order 

46
from Tiltman for the meeting was “to keep his mouth shut.” This 

led to the perception that there was no agreement within the British 

contingent, let alone between the British and the Americans. The 

U.S. was quick to pick up on the perceived disagreement amongst 

the British, and equally quick to try to exploit it. It took considerable 

skill on Tiltman’s part to enforce discipline within his own “ranks” 

while continuing a dialogue with the Americans that would not put 

previous efforts for unity at risk over this single issue. 

An agreement was finally reached, despite continued vocal 

opposition from the Royal Air Force representative. He objected 

particularly to American insistence on use of the M-209 cipher 

system. He had to be convinced that the U.S. was pushing for its use 

in part because there were 200,000 of them lying about unused. 

(Actually, there were only 100,000 of them, but Tiltman used the 

higher figure, perhaps for dramatic effect.) It was eventually agreed 

that the British would continue working to develop a frequently 

changing digraphic code, and that the M-209 would be held in 

reserve should the British be unable to deliver. Tiltman found an 

ally in William Friedman, and together they agreed that in the future 

codes and ciphers would be developed jointly, thereby alleviating the 

need to retroactively patch together a fit for incompatible systems.

The real test of his skills, however, had nothing to do with 

the delegation he led, or the subject they were sent to deal with. 

Separate from Tiltman’s visit, Alan Turing, the brilliant British 

mathematician who was responsible for British development of 

the bombe, among other contributions, arrived in the U.S. His visit 

arose from an invitation from the U.S. Army chief signal officer to 

the British to send over an expert to see a new piece of equipment 

that was being developed for speech privacy (this would become 

the SIGSALY system). While Turing was en route, General Strong, 

the intelligence officer (G-2) for the chief of staff, General Marshall, 

blocked Turing’s proposed visit to Bell Laboratories, where the 

system was being developed.

 Several reasons have been advanced for General Strong’s action. 

One involved a member of Strong’s staff, another general who 

47
had ties to ITT, the company working with U.S. cryptographers to 

develop SIGSALY. Tiltman maintained that he was told by Carter 

Clarke, then chief of the Special Branch of the U.S. Army’s Military 

Intelligence Division, after the incident was finally resolved, that 

this general, misinterpreting what was meant by “exploitation,” 

persuaded Strong to block Turing’s visit. The general believed that 

commercial exploitation was at issue, and that the British would use 

their access to threaten ITT’s business interests once the war was 

over. Tiltman could not vouch for the accuracy of this explanation; 

he merely offered it as what he had been told by a person he 

respected.

Probably closer to the truth, based on the negotiations that 

finally broke the impasse, was that Enigma had once again reared 

its divisive head. The U.S. Army remained convinced that the British 

were withholding information from them, information that would 

have enabled the Americans to better pursue their own desire to 

exploit the German encryption machine. Apparently, the Americans 

saw the British request for Turing’s access to SIGSALY as a wedge 

they could use to force the British to be more forthcoming with 

Enigma technical information and raw traffic intercept. It should be 

noted that the U.S., at this stage of the war, was entirely dependent 

on British collection efforts against the European Axis. Whatever 

Enigma intercepts there were that interested the Army came from 

the British because the Americans had no collection sites in a 

position to pick up German messages. 

Whatever the cause for the dispute, Tiltman received orders to 

intervene with his American contacts to resolve the issue. In fact, he 

was told not to return to the UK until he had achieved a successful 

resolution. At first he met with reluctance on the part of Strong 

to even discuss Turing’s visit. Several long meetings were held in 

which Strong skillfully kept the Turing topic off the agenda. In 

each case, Tiltman had been accompanied by British naval captain 

Hastings, whose job was to represent both the SIS and GC&CS 

with the Americans. Tiltman was then informed by Brigadier 

Dykes, staff officer to Field Marshal Sir John Dill, the senior British 

representative in Washington, that Hastings was, in fact, part of 

48
the problem. According to Dykes, Strong did not like Hastings, and 

would not discuss the Turing visit while he was present. Accordingly, 

Tiltman prevailed on Hastings to bow out, and he met with Strong 

by himself. As he later recalled, this did not significantly improve 

matters at first. Instead, he was treated to another two hours of the 

general covering every subject imaginable, except the Turing visit. 

In the middle of this, Strong stopped, and said “I know you think 

that I have horns and cloven hooves,” which left Tiltman wondering 

whether the proper response was “Yes, Sir!” or “No, Sir!”

Tiltman also faced the added complication of a deadline that was 

caused by the impending Casablanca Conference. Since virtually 

everyone who could work to break the impasse would be leaving 

Washington for the conference, Tiltman had to move quickly. 

Throughout mid- to late December, Tiltman continued to meet with 

U.S. officials, especially Clarke and then, in January 1943, again with 

Strong himself to convince them that no Enigma information that 

could endanger American lives or operations was being withheld. By 

early January he was able to convince Strong of that fact, but then 

faced opposition from Britain. He recommended that the U.S. be 

allowed to send permanent representatives to Bletchley Park who 

would have full access to every aspect of Enigma exploitation so that 

the Americans would have no cause to express similar doubts about 

British cooperation in the future. 

It finally took a direct exchange of letters between Field Marshal 

Sir John Dill, the former chief of the Imperial General Staff and, in 

1943, the senior British representative in Washington (and also a 

close personal friend of General Marshall) to George Marshall, the 

Army chief of staff, to break the deadlock in January. And it took a 

thinly veiled threat from the British that continued opposition to 

Turing’s visit could endanger further cooperation on the Enigma 

problem to finally turn the trick. On 9 January, after almost a month 

of wrangling, the acting chief of staff (Marshall had already left for 

Casablanca) informed the British that Turing’s visit to Bell Labs had 

been approved. 

49
Dill’s intervention became possible, and effective, only because 

Tiltman was there, assuring both the senior British representative 

and the Americans that Enigma information was indeed flowing 

between the allies. His words to Dill were typical of his efforts: 

“We make available to any properly accredited representative of 

the War Department all the processes and results of cryptographic 

investigation at the Government Code and Cypher School, but in 

the case of investigation on the higher planes of secrecy we have 

discouraged as far as possible the duplication of our work in the 

U.S.A. or elsewhere.”

 Of course, his “but” clause lay at the heart of the dispute. The 

U.S. Army did not want to play second fiddle on this issue. It wanted 

full access to not only the results of Enigma decryptions, but also the 

raw intercept and the bombes that made the decryptions possible. 

The Americans fully believed they could build a better bombe (which, 

in the case of the Navy, they wound up doing). Some of the British 

cryptographic leaders remained wedded to increasingly outdated 

concepts of security, and sought to keep the secrets of the bombes to 

themselves. Tiltman might have had to present their position to Dill 

and to the Americans, but it became increasingly clear during the 

war that he did not share their view. He pushed for full cooperation 

between the U.S. and British cryptologic services, a position he had 

taken up as early as 1941. Retrospectively, it is obvious that Tiltman 

was riding the wave of the future, and his efforts were instrumental 

in breaking down British reluctance to deal completely openly with 

the Americans. By 1943, largely through his persistence, an influx 

of Americans was arriving at Bletchley Park to reinforce the British, 

and to learn from their more experienced colleagues. After the war, 

he did not hesitate to point out the importance of this infusion of 

new blood. 

Tiltman also recounted that it was during this visit in late 1942 

and early 1943 that he almost met with General William Donovan, 

the head of the American Office of Strategic Services (OSS). A 

meeting of the two was arranged through Captain Hastings and 

Sir William Stevenson, who headed British security coordination 

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and worked out of New York City. Tiltman traveled to New York 

and met Stevenson at the St. Regis Hotel. When told that Donovan 

wanted to talk to him, Tiltman agreed, but only if the discussion 

did not involve SIGINT exchanges between the Americans and 

the British. As Tiltman explained to Stevenson, he had just taken 

“a frightful beating” from Admiral Redman, and had been warned 

that he would remain a “friend” as long as he confined his dealings 

to the Army and the Navy. Redman was very clear that he should 

avoid having anything to do with “any other organizations.” Based 

on that, Stevenson agreed to concoct a story about Tiltman missing 

connections to New York, and the meeting with Donovan never took 

place. It fell victim to the internecine feud between the established 

U.S. military cryptologic elements and the new kid on the block, the 

OSS. 

Mission accomplished with regards to Turing, Tiltman returned 

to Britain in late January. As an aside to the whole imbroglio, 

Tiltman was asked years later if he had accompanied Turing to 

Bell Labs. He answered that he had not. In fact, he was never really 

sure what equipment Turing was supposed to inspect, and was sure 

he would not have understood it in any case. As for Turing, after 

overcoming a bit of unpleasantness when he was almost detained at 

Ellis Island because of insufficient documentation, he had spent the 

month during which he was the center of the storm with friends on 

Long Island, well away from the turmoil.

Back at Bletchley, Tiltman continued to devote his energies to 

attacking enemy ciphers, to securing British ones, and to fostering 

inter-Allied cooperation (especially with the Americans). Efforts to 

promote such cooperation were finally formalized through a series 

of agreements including the one between GC&CS and the U.S. Army 

signed on 17 May 1943 (the Travis-Strong Agreement, named after 

its two signatories). It, and an earlier agreement between the U.S. 

Navy and GC&CS, represented the beginning of a unique SIGINT 

agreement between foreign powers. Exchange of ideas, technology, 

and talent became a two-way street. Not only, as we have seen, did 

large numbers of Americans arrive at Bletchley, but a smaller, but 

51
still significant, number of Britons came to Washington to work with 

both the Army and Navy cryptologic services. 

In spite of increasing administrative responsibilities, Tiltman 

did not forget his technical roots. He continued to assist, as time 

permitted, on sustained efforts against Japanese systems. Given 

British priorities, Japan had always taken a backseat to efforts 

against German cryptographic systems, and Japanese military codes 

and ciphers had lagged in importance behind Japanese naval ones. 

This picture began to change in 1943. The balance between Japanese 

systems changed somewhat at about this time. The disparity that had 

existed since before the war began between intercepts of Japanese 

naval and military communications had been largely rectified. As 

a result, the cryptanalysts began to have success against Japanese 

military codes and ciphers. Tiltman thought that the time was right 

to launch a more sustained and better-coordinated attack. He was 

instrumental in calling a conference at Bletchley of senior allied 

personnel working the Japanese systems. Agreement was reached to 

have the British concentrate on Japanese Army Air Force systems, 

while Arlington Hall would take over high-level systems used by 

Japanese ground forces. Central Bureau, a joint Australian-U.S.-

UK effort working out of Australia, would work low-level military 

material. 

By March 1944, Tiltman was back in Washington, this time 

accompanying Travis (head of GC&CS) and L. J. Hooper (head of 

the new Japanese Forces section which had been established in 

GC&CS after the Italian Armistice had made more staff available, 

and who would be director of GCHQ from 1965 to 1973) and others 

at a second conference on Japanese military codes. The expanding 

nature of the cooperation between the English-speaking allies was 

demonstrated by the fact that the British and Americans were joined 

this time by representatives from Canada and Australia.

Tiltman’s efforts received de jure recognition by the British of 

the roles he had taken on during the war years. In the March 1944 

reorganization he became one of the five deputy directors of GC&CS. 

In June he was promoted to brigadier (later many of his colleagues 

52
58

would be unable to remember exactly when he had officially been 

promoted, they could only ever remember calling him “the Brig”). 

These formal elevations did not, however, induce him to give up 

playing a significant role in the technical aspects of the business. 

In the summer of 1944 he was asked to turn his formidable powers 

against improvements that Japanese Navy had made to the JN-25 

code they had used throughout the war. The Japanese had been 

alerted to the fact that their code might be exploitable by the rather 

injudicious use some American field commanders had been making 

of the intelligence provided to them. While a complete replacement 

of the code was logistically impossible given conditions the Japanese 

were operating under by 1944, they were able to implement security 

improvements. These changes led to a sixty percent loss of strategic 

intelligence, and the danger that Allied insight into Japanese naval 

order of battle was on the verge of becoming obsolete. Increased 

cooperation between the Americans and the British, and the efforts 

of people like Tiltman, eventually rectified the situation, and 

intelligence began to flow once again in a timely fashion.

Tiltman was back in the U.S. in late 1945, again with Travis, for 

negotiations to convert the wartime agreements into a document that 

would continue the relationship into the peace years. Unfortunately, 

the legacy of Enigma once more intervened. The U.S. hosts were 

headed by Admiral Redman, the same person who had attacked 

Tiltman over the perceived failure to be forthcoming with Enigma 

data in 1942. 

Redman took the occasion to revisit the difficulties surrounding 

Enigma, and singled out Tiltman again as in some way responsible. 

What irritated Tiltman the most was that he knew that Redman 

was fully aware that it was largely through Tiltman’s intervention 

that the impasse had been broken, in the Americans’ favor. Tiltman 

held his fire during the session, but after it was over he told Travis 

that he refused to reenter the room as long as Redman remained in 

the chair. Every attempt by Travis to calm him down failed, and he 

withdrew from the negotiating process, depriving both sides of the 

benefit of his experience and wisdom.
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Postwar Experiences

With the war over, GC&CS became the Government 

Communications Headquarters (GCHQ) in 1946, and Tiltman was 

named an assistant director in 1947. He added one more “retirement” 

to his resumé, this one from the military (for the second time) the 

previous year. He was then named as the senior UK liaison officer 

(SUKLO) to the U.S. in 1949, working out of the British embassy in 

Washington until the next of his “retirements,” this time his formal 

one from GCHQ in 1954, at the age of sixty. By special arrangement, 

and in recognition of his talents, he was allowed to continue working 

for GCHQ for another decade, including a stint as an integree at NSA 

from 1958 to 1964, finally stepping down from British service at the 

age of seventy in 1964. 

During this period of his life, he became interested in one of the 

more puzzling items in the long history of cryptology, the Voynich 

Manuscript. This book, which now resides in the Yale University 

Library, is claimed by some to have been written by the thirteenth 

century English scholar Roger Bacon. More likely, it was written 

in the late sixteenth or early seventeenth century and attributed to 

Roger Bacon in an attempt to embellish its mystique, and to drive 

up the price that was asked of the Holy Roman Emperor, Rudolph 

II, an inveterate yet gullible book collector. It is a combination of an 

unknown script and colored pictures that appear to represent plants, 

astrological or cosmological material, pharmaceutical recipes, and 

human figures surrounded by bizarre objects. 

It has attracted the attention of numerous cryptanalysts, with the 

two most prominent being Tiltman himself and William Friedman. 

It is perhaps no mystery why men of their talents would be drawn 

to a text that one would assume had meaning. Friedman seems 

to have caught the bug first and drew Tiltman’s attention to it in 

about 1951. Friedman devoted sporadic interest to it until his death 

in 1969, while Tiltman’s interest seemed to wane sometime in the 

1970s. Neither of them arrived at a solution, but then again, neither 

has anyone else. One could speculate that if two of the greatest 

cryptologic minds of the twentieth century could not unravel the 

mystery of the manuscript, then perhaps there really is nothing 
60

there to unravel, and the Voynich Manuscript is nothing more than 

a hoax. 

Tiltman’s contributions to the cryptologic world, and to UKU.S. SIGINT relations, did not end with his “retirement” in 1964. 

He moved to the U.S. to be closer to his daughter, and became a 

consultant to NSA. Ironically, it took special intervention by the 

director of the Agency for this “foreigner” to clear the security 

hurdles, and fortunately sanity prevailed. He lent his expertise 

to working a number of hand systems still in use in a number of 

Eastern European and Third World countries. 

His years at NSA were used by GCHQ to help smooth over a 

potential problem that came in the form of a soon-to-be-published 

book. In 1966 a relative newcomer to the world of cryptologic writing, 

David Kahn, was preparing to release his groundbreaking book The 

Codebreakers. Prepublication hints of what the book would contain 

caused considerable consternation among the cryptologic services on 

both sides of the Atlantic. Tiltman was asked by GCHQ to approach 

Kahn and get him to remove any reference to itself, its location, or 

its director. The negotiations were successful, so when the book 

appeared in 1967 it was met with a great deal more equipoise in the 

UK than greeted it in the U.S.

He also recounted a second encounter with Kahn, this time 

when Kahn tried to interview him as a source for his writings. Kahn 

singled out Tiltman as the top technical man in the field, but the 

Brig would not budge from his position that his view of what was 

required of him because of his oaths to maintain security precluded 

him from being connected with any attempt to reveal the secrets 

which he had learned over a lifetime of service. He would make it 

clear, however, that he bore no ill will towards Kahn, and indeed had 

cooperated with him when the subject had turned to Tiltman’s work 

on the Voynich Manuscript.

He did not feel the same way towards others who chose to write 

about cryptanalytic efforts that he had been involved in, especially 

when he considered that those writers were bound, as he believed 
61

himself to be, by an oath to preserve the secrecy of their endeavors. 

He felt this oath was a lifetime obligation, not one to be laid aside 

at the time of retirement. He was particularly critical of the work of 

F. W. Winterbotham, the former SIS officer who first revealed the 

Enigma story in the mid-1970s. Tiltman knew that Winterbotham’s 

book, The Ultra Secret, was riddled with inaccuracies. 

Not the least of these is the myth that Churchill had received 

warning through Enigma exploitation that the Germans had planned 

a large-scale air raid against the city of Coventry in early November 

1940. The myth maintains that, to protect British exploitation 

of Enigma, Churchill refused to allow the city to be warned or 

evacuated. Just on the surface, there are several flaws with this 

story. First, all British cities were aware in 1940 that they might be 

the targets of German air raids. Second, evacuating an urban area 

would likely have caused more problems than it solved. The impact 

of Hurricanes Katrina and Rita in the U.S. in 2005 more than 

demonstrates the difficulties that result from attempts to evacuate 

large urban areas, even with twenty-first century technology. What 

lay behind the myth involved British exploitation of another piece 

of German technology, namely the beam system the German air 

force used to guide their bombers to their targets. The British were 

able, before the Coventry raid, to intercept part of the beam system, 

but they needed to know the intersection point (that is, where the 

Germans would release their bombs) of the beams, as well as the 

frequencies being used to transmit them. The intersection point 

became known on the afternoon of the raid, and British scientist 

R. V. Jones correctly surmised the frequencies. Jamming efforts 

failed, however, because the Germans used sophisticated filters that 

enabled their systems to ignore the jamming signal. 

More damaging in the Brig’s eyes was the precedent set by the 

work, which opened the floodgates for others to publish works on 

subjects he felt should have been kept from public sight, at least until 

fully documented histories could be officially released by scholars 

who had complete access to the information. He felt that to allow 

the Winterbothams of the world free rein was to make a mockery of 
62

the hundreds who went to their graves keeping the secrets they had 

sworn to keep.

Insights on Cryptology

During his years at NSA, Tiltman continued his life-long efforts 

to educate those who would take up the task once he finally, finally 

set it down. In doing so, he laid down a number of principles for 

cryptographic security that have enduring value, decades after 

he stated what has since become the obvious. These were lessons 

learned over a lifetime of devoted service:

	 Any cipher system is a compromise between security and 

practicability.

	 Responsibility for the security of a system has to be taken 

completely out of the hands of the cipher operator. It has to be proof 

against attempts by holders to circumvent instructions through 

laziness.

	 A system is only as strong as its weakest link. Cryptanalysts 

make their living out of the sloppy thinking and enthusiastic overingenuity of designers. The possible damage from compromise has 

to be taken into account when the system is assessed, in advance of 

its use.

	 All transposition systems are dangerous. They are vulnerable 

to special circumstances thrown up by chance, and it is difficult for 

the designer to eliminate such possibilities absolutely.

	 Usage of a system should be periodically monitored to 

ensure it is not being overloaded.

	 Many systems have been ruined by reliance for security on 

variant substitution units.

	 Tailing and trailing are used to ensure even overall use of 

long, though limited key.
63

	 Stereotyped openings and signatures are often unavoidable. 

Security is achieved by bisection or by the use of a separate system 

for stereotyped material.

	 Otherwise secure systems will be ruined by inadequate 

indicating systems.

	 It may take only one bust to ruin security of an otherwise 

sound system.

	 One-time pads don't have to be absolutely random, just 

unpredictable.

	 Ciphers have to be specially designed for proforma reports.

	 It is the absolute responsibility of experienced cryptanalysts 

to pass on their knowledge. [Tiltman had no use for those who 

create an aura of mystery around their work to enhance their own 

importance.]

	 The most badly documented aspect of work against a cipher 

system is the initial break-in. This documentation usually occurs 

well after the event, and details are often forgotten.

Tiltman consistently maintained that the justification for the 

effort put into SIGINT (always a very expensive venture) is that it is 

a weapon of defense. He insisted that, in addition to attacking the 

sophisticated systems of opponents, less sophisticated systems and 

the systems used by less important states should not be ignored. 

This stemmed from his belief that SIGINT is relatively cheap only 

if it can be carried out as expeditiously as possible, and that means 

gaining insight into a country’s cryptologic practices early on in the 

game. It also meant recognizing that information derived from less 

sophisticated systems could often prove useful as cribs for breaking 

into the more sophisticated ones. 

Further, speed of thinking and speed of operation were essential 

in this process; otherwise, the intelligence gathered would be dated 
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and not worth the price paid at all. All of this required a breadth and 

depth of experience, factors he felt were being increasingly neglected 

in the development of budding cryptanalysts, a neglect he feared 

would have future, negative repercussions.

As he spent time reflecting on his long career, Tiltman was able 

to admit to having fallen victim to a certain amount of parochial 

thinking that clouded his approach to organizing GCHQ just 

before the end of the war. He had been, and at heart remained, a 

cryptanalyst. He admitted that, as a result, he had come to have little 

appreciation for the contributions other skills, particularly traffic 

analysis, could bring to the table. In later years he regretted that 

shortsightedness, especially as he watched cryptographic systems 

become increasingly complex and unbreakable, a situation that 

called more and more for the attributes of the traffic analyst to be 

brought to bear.

End of Career/Legacy

Throughout Tiltman’s career, his contributions were 

acknowledged and rewarded by both the U.S. and Great Britain. 

In 1930 he was made on Officer of the Order of the British Empire 

(OBE), and was advanced to a Commander of the British Empire 

(CBE) in 1944. To this was added the honor of Companion of the 

Order of St. Michael and St. George (CMG) in 1954. On this side of 

the Atlantic, he was honored with the Legion of Merit in 1946. Some 

of his contemporaries expressed surprise in later years that he was 

never knighted by the British monarch, but he was not high enough 

in the hierarchy to warrant that distinction (only the director of 

GC&CS was so honored). 

The Brig finally really retired in 1980, after sixty-six years of 

singular service to two nations; sixty of those years were devoted 

to cryptologic work where his insights and innovations benefited 

both the cryptographic and cryptanalytic disciplines. He moved to 

Hawaii, again to be near his daughter, and passed away in 1982. He 

stands among the giants of cryptology, a status NSA acknowledged 

by placing him in its Hall of Honor in 2004. 
65

The legacy Tiltman left is a large one. From breaking Russian 

diplomatic and Comintern systems in the 1920s and 1930s, he 

moved on to seminal efforts against Japanese military and naval 

systems in the 1930s and 1940s. To these accomplishments he added 

the insight that made exploitation of major German systems such as 

Tunny possible. His skills were not limited to the exploitation of 

systems used by his country’s foes, but extended to the other side 

of the cryptologic mission. The systems he created to protect British 

and allied signals provided reliable and much-needed security. 

He continued after the war, through the 1950s, 1960s, and 1970s, 

to successfully attack systems devised by countries considered to 

be of national interest to both Great Britain and the U.S. No less 

importantly, he helped cement relations between the U.S. and his 

native Britain, a partnership that continues to benefit both nations.

To these technical and partner-building skills he added personal 

attributes of integrity and loyalty and a keen, almost fierce, desire to 

impart his skills to the young. He sought to inspire them to a level of 

success they otherwise would have thought unattainable. It was not 

hyperbole when Sir Brian Tovey, director of GCHQ, praised Tiltman 

as one of the greatest cryptanalysts Great Britain has ever produced. 

His long list of accomplishments deserves no less an accolade.

John F. Clabby

Center for Cryptologic History
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