Historical Document · 2016
The Sinkov–Rosen–Weeks–Currier mission with the PURPLE analog, Friedman's illness, crates memo (64 pp); cited throughout the PURPLE unit but not yet in the Library
United States Cryptologic History The First Americans The 1941 US Codebreaking Mission to Bletchley Park Special series | Volume 12 | 2016 Center for Cryptologic History David J. Sherman is Associate Director for Policy and Records at the National Security Agency. A graduate of Duke University, he holds a doctorate in Slavic Studies from Cornell University, where he taught for three years. He also is a graduate of the CAPSTONE General/Flag Officer Course at the National Defense University, the Intelligence Community Senior Leadership Program, and the Alexander S. Pushkin Institute of the Russian Language in Moscow. He has served as Associate Dean for Academic Programs at the National War College and while there taught courses on strategy, international relations, and intelligence. Among his other government assignments include ones as NSA’s representative to the Office of the Secretary of Defense, as Director for Intelligence Programs at the National Security Council, and on the staff of the National Economic Council. This publication 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 US government entity. This publication is distributed free by the National Security Agency. If you would like additional copies, please email [email protected] or write to: Center for Cryptologic History National Security Agency 9800 Savage Road, Suite 6886 Fort George G. Meade, MD 20755 Cover: (Top) Navy Department building, with Washington Monument in center distance, 1918 or 1919; (bottom) Bletchley Park mansion, headquarters of UK codebreaking, 1939 UNITED STATES CRYPTOLOGIC HISTORY The First Americans The 1941 US Codebreaking Mission to Bletchley Park David Sherman National Security Agency Center for Cryptologic History 2016 Second Printing Contents Foreword.................................................................................. 1 The Mission’s Political and Military Context......................................... 4 A Technical Exchange Takes Shape: The Tizard Mission............................ 7 The Genesis of a Signals Intelligence Exchange.................................... 10 Continued Progress in Technological Cooperation................................. 13 The State of American and British Cryptanalysis in Mid-1940.................... 16 The American Team Is Chosen. ....................................................... 19 The Voyage to Britain. ................................................................. 21 Settling into a Routine................................................................. 25 What the Americans Learned at Bletchley Park.................................... 26 Breakthrough: The British Decision to Disclose Enigma........................... 28 The Americans, the Enigma, and the Bombe....................................... 29 Travels Away from Bletchley Park.................................................... 31 London. ............................................................................. 32 Other Locations Visited........................................................... 33 The Mission Returns to the United States........................................... 37 Assessment: Was the Sinkov Mission a Success?.................................... 39 Notes...................................................................................... 42 The First Americans Foreword Folk wisdom in most cultures has much to say about the importance of good beginnings and positive first impressions. The many sayings about this are true, and they apply not only to individuals but also to groups and even government organizations. Britain and America in communications intelligence. He emphasizes the dire situation confronting the Allied nations in 1940 and 1941, and how they decided on intelligence cooperation as one way to meet it. The truth about good beginnings and positive first impressions is strongly illustrated by the development of the secret relationship between the United Kingdom and the United States in communications intelligence (COMINT) in World War II. The bilateral cooperation grew in range and depth of coverage and has continued over time; it has lasted from World War II until the present day. Most significantly, Dr. Sherman emphasizes the people involved in the first COMINT contacts. The actions and reactions of a few key people, the impressions they made on each other, became the vital factor in determining the new policies on intelligence in their respective nations. Ultimately, what grew from their initial interactions helped change the course of history—many times. The strong links and enduring quality of this intelligence-gathering relationship between two nations were not automatic or inevitable. Their closeness and longevity—and voluntary nature—are unprecedented in history. Dr. Sherman’s book is important professional reading for historians and intelligence practitioners alike. One major factor in the development of this amazing relationship was its good beginning. It started a little tentatively, but both nations quickly recognized the professionalism of the other and, most importantly, quickly learned to trust and rely on the other. It is also a whopping good tale, well told. David A. Hatch, NSA Historian Dr. David Sherman has written a fascinating narrative of the first professional contacts between 1 1 The First Americans 2 The First Americans The 1941 US Codebreaking Mission to Bletchley Park In late January 1941, ten months before Pearl Harbor and America’s entry into World War II, a four-person US military delegation slipped onto the British battleship HMS King George V, which was anchored in the Chesapeake Bay off Annapolis, Maryland. Wearing civilian clothes, carrying diplomatic passports, and armed with the cover story of being Canadians, the four officers—the US Navy’s Prescott Currier and Robert Weeks and their US Army companions Leo Rosen and Abraham Sinkov, the group’s leader—were bound for a British installation so secret that for three decades after the war’s end in 1945 it remained unknown to the general public in both Great Britain and the United States. This was Bletchley Park, the United Kingdom’s wartime codebreaking establishment located on a former country estate an hour’s train ride north of London. The home of “the Ultra Secret,” or the breaking of Germany’s supposedly impenetrable Enigma encryption system protecting the Reich’s most sensitive military communications, Bletchley Park had never before been visited by any foreigners, American or otherwise. Winston Churchill himself, while well aware of Bletchley Park’s existence and the critical importance of its activities, did not set foot there until September 1941. The British government at first set significant limits on what the Americans could see or be told about Bletchley Park’s codebreaking effort. In particular, discussions of the Enigma were ruled out of bounds. The Americans’ disclosure of their successful cryptanalysis of the Japanese “Purple” code—used by Tokyo to protect its highestlevel diplomatic communications—and their gift of a replica of it invented by the army’s Signal Intelligence Service (SIS), a device which became known as the “Purple analog,” persuaded London to reverse its previous position of excluding the Enigma from discussion and share with the Americans its success against the German cryptosystem, including its engineering of the “bombe” cryptanalytic machine. During the final leg of their voyage across the Atlantic, the Americans would be strafed by the German Luftwaffe and, above the waves of the North Sea, see the tops of British merchant vessels sunk by German bombs. Some of the British naval officers they traveled with had lost family members during the Blitz. Having arrived in southern England, they would gain a first-hand look at wartime Britain which few Americans—most notably the radio journalist Edward R. Murrow—had experienced by the winter of 1941. While at Bletchley Park, they would hear the sounds of German bombing in the distance. Visiting London itself, they would see the devastation wrought by the Nazi aerial onslaught on 3 The First Americans The American delegation to Bletchley Park: Navy officers Prescott Currier (top), and Robert Weeks . . . its docks and underground stations and would spend an evening at a café which within the week suffered a direct hit by a German bomb and major loss of life. After the delegation returned to the United States, some American military intelligence officers apparently questioned whether it had been a success. As for the British, it seems to have had little immediate impact on their activities for the remainder of 1941 and into early 1942, especially given that they remained locked in a life-or–death struggle with Hitler’s Germany and—for the moment, at least—possessed cryptanalytic capabilities which had progressed far beyond those of the Americans. For the four American participants, however, there was no doubt about the value of what they had seen and learned at Bletchley Park. Their ranking officer, Sinkov, believed the experience at Bletchley Park would save American codebreakers two years of intense work on German and Italian cryptosystems. The four Americans would not be the last to visit Bletchley Park. Two years later, in the summer of 1943, the first of what ultimately would come to over 200 Americans arrived as full members in what was now a codebreaking partnership between the two Allies, the United States and the United Kingdom, a partnership which would become a critical element in their ultimate victory over the Axis powers and, in the war’s aftermath, endure as a key component of the West’s containment strategy vis-à-vis the Soviet Union. The Mission’s Political and Military Context In the spring of 1940, the armed forces of Hitler’s Germany deployed the unprecedentedly mobile style of warfare which came to be known worldwide by its German name, Blitzkrieg, to overrun in rapid succession the Scandinavian nations, the Netherlands, Belgium, and—most significantly—France. The army which Great Britain had sent to the continent to aid its French ally had been surrounded at the coastal city of Dunkirk, from which it was evacuated 4 The First Americans successfully but without most of its heavy equipment. With the undefeated German army, navy, and air force now occupying bases from the North Sea to the English Channel and France’s Atlantic coast, it seemed only a matter of time—notwithstanding the appointment of the defiant Winston Churchill as prime minister—before London was forced to surrender or sue for peace, regardless of whether this resulted from a German invasion of southern England or the strangulation of Britain’s overseas supply lines by Hitler’s U-boats.1 . . . and army officers Abraham Sinkov (top) and Leo Rosen (photos taken later) The swift and successive German victories in the spring of 1940 also spurred American President Franklin D. Roosevelt to take a more assertive stance toward aiding Britain in the face of continuing isolationist opposition to becoming entangled in the European conflict. Speaking at the University of Virginia’s commencement exercises on June 10, following Italy’s invasion of an only lightly defended southern France which he denounced as a “stab in the back,” Roosevelt vowed that “we will extend to the opponents of force the material resources of this nation and, at the same time, we will harness and speed up the use of these resources in order that we ourselves may have equipment and training equal to the task of any emergency and every defense.”2 Five days earlier, and in response to a plea for assistance from Churchill, Roosevelt began shipping arms and ammunition to Britain that had been declared surplus by Army Chief of Staff George C. Marshall. The day before France signed its armistice with Germany, June 20, he reshuffled his cabinet, nominating interventionist Republicans Henry Stimson and Frank Knox to serve as the secretaries of war and the navy. That same day, the Selective Service Act, which proposed the first peacetime draft in American history, was introduced in the Senate. It was filed in the House the next day.3 However, despite Churchill’s courageous “never surrender” rhetoric, there were those in Britain dur- 5 The First Americans Prime Minister Winston Churchill (l) and President Franklin Delano Roosevelt ing the early summer of 1940 who harbored doubts as to whether their nation could endure against Berlin’s seemingly unstoppable military juggernaut. Germany’s rapid military successes also kindled such doubts among some American political and military leaders. The American ambassador in London, Joseph Kennedy, was particularly skeptical about the United Kingdom’s ability to withstand the German onslaught. Accordingly, in July, Roosevelt sent William Donovan—the future head of the wartime Office of Strategic Services, or OSS—to London to assess not just British resolve but, perhaps more significantly, its capability to continue the war against the Axis. As Roosevelt’s personal envoy, Donovan was given access to Churchill and the British high command. He also met with Stewart Menzies, the chief of Britain’s Secret Intelligence Service, MI-6, and the titular head of the codebreaking operation at Bletchley Park, which at the time was experiencing its first successes 6 against the Enigma. While Menzies said nothing of Bletchley nor of its progress in breaking the German cryptosystem, a feat which ultimately would become the most important contribution of British cryptanalysts to the survival of Britain, he did tell Donovan that, in the words of Donovan’s biographer Douglas Waller, “he was confident the Luftwaffe’s moves over British skies could be anticipated.”4 Having returned to the United States in early August fully persuaded that Britain would survive, Donovan joined Roosevelt and Secretary Knox on a trip to New England for an inspection of the navy yards at Boston and Portsmouth, New Hampshire. After a series of conversations, first on the train north and then on the presidential yacht as it sailed between the two ports, Donovan felt that he had successfully convinced Roosevelt of London’s ability and will to continue the war. In the view of one scholar who has studied Donovan’s visit to Great Britain, “it was a key factor in his [Roosevelt’s] decision in August The First Americans to transfer fifty overage destroyers to Britain,” something Churchill had requested that Roosevelt do as early as the day after the latter’s pivotal speech to the University of Virginia’s graduating class. Having returned to Washington, Roosevelt pushed ahead with the destroyer deal. In early September, Roosevelt and Churchill agreed to an arrangement whereby the destroyers would be transferred to the Royal Navy in exchange for American basing rights on British territories in the Western Hemisphere.5 A Technical Exchange Takes Shape: The Tizard Mission In the meantime, a separate series of events had moved Great Britain and the United States toward a joint discussion of their most advanced military technologies. Roosevelt’s increasing tilt toward London may have established the necessary political context for the cryptanalytic exchange that began when the four American officers visited Bletchley Park in early 1941, but this shift in his administration’s policy toward Britain by itself likely would have proven insufficient to trigger one. If there was a catalyst, it may well have been the budding secret technical dialogue between the two nations which began to emerge in the summer of 1940. In the period leading up to the war and then for much of its first year, efforts by the two nations to start a conversation on secret defense systems invariably had come to nothing. Attempts by the British to gain access to the America’s Norden bomb sight, which allowed aircraft to deliver munitions with great precision from high altitudes, were repeatedly rebuffed by the heads of the US Army and US Navy. London’s offer to share its ASDIC antisubmarine warfare capability was similarly fruitless, especially after it learned that the naval technologies Washington might offer in return were either not as advanced as what the British already had or by US law could not be provided to a foreign military. However, a week before Donovan departed for London, the British ambassador in Washington, US Army Chief of Staff General George C. Marshall (photo taken near end of war) US Secretary of War Henry Stimson Philip Kerr, Lord Lothian, made a direct appeal to Roosevelt. “The British Government have informed [sic] me,” he wrote, using language drafted by the Air Ministry and cleared by the Admiralty and the For7 The First Americans dum to Roosevelt by indicating that “for our part, we are probably more anxious to be permitted to employ the full resources of the radio industry in this country [the United States] with a view to obtaining the greatest power possible for the emission of ultra short waves than anything else.” In June, however, Congress had passed the Walsh Amendment, named after the isolationist Massachusetts Senator David Walsh, forbidding the sale of US military equipment to another nation unless General Marshall and Chief of Naval Operations Admiral Harold Stark certified it as surplus materiel not essential to American national defense. Stimson thus insisted that any items which the US Admiral Harold R. Stark (l) and Secretary of the Navy British wanted to procure from US Frank Knox on a train in the UK, 1943 industry would have to be approved by Marshall and Stark as not interfering eign Office, “that they would greatly appreciate an with US efforts to increase military preparedness.7 immediate and general interchange of secret techniActing Secretary of State Sumner Welles included cal information with the United States, particularly this proviso in a letter he sent to Lothian on July 29 in the ultra short wave radio field.” London had no confirming the administration’s readiness to receive intent, he continued, of making this arrangement “a a “small secret British mission for technical and scibargain of any description” but rather was ready to entific discussions.”8 send a small group of British military officers and civilian scientists to the United States “to give you the full details of any equipment or devices in which you are interested without in any way pressing you beforehand to give specific undertakings on your side.” Naturally, Lothian concluded, his government “would hope that you would reciprocate by discussing certain secret information of a technical nature which they are anxious to have urgently.”6 Lothian’s proposal was discussed at a cabinet meeting on July 11, where Secretary of War Stimson and Secretary of the Navy Knox supported the British initiative. Roosevelt then decided to accept it and press forward. There was, however, an important caveat. Lothian had concluded his memoran8 Churchill, who by virtue of his membership on the Air Defense Research Committee during the 1930s was well aware of British progress on radar, initially had been skeptical upon becoming prime minister about sharing this technology with the United States. However, by June 1940, his military leaders had swung behind the idea. On June 30, Churchill authorized Air Minister Archibald Sinclair to proceed with the proposed technical mission on the condition that “the specific secrets and items are reported beforehand.”9 A month later, on July 25, having received advance word of Welles’s letter giving the go-ahead for the mission, the British War Cabinet directed, in the words of one recent histori- The First Americans William Donovan, head of the wartime Office of Strategic Services an of the discussions regarding a technical exchange, Steven Phelps, “all service branches to prepare lists of the technology to be handed over to the Americans.” It also “made clear that disclosure must be full and open.”10 Both London and Washington spent August preparing for the British mission. On August 1, the scientist Henry Tizard was appointed to head what would become a six-person group, which met for the first time on August 10. Tizard departed for the United States on August 14—the day after “Eagle Day,” which marked the Luftwaffe’s launching of the assault which became known as the Battle of Britain—as the mission’s advance man, arriving in Washington via Ottawa eight days later. On August 26, he met with Roosevelt at the White House. The next day, he met with Stimson, who may have arranged for an August 29 briefing by Tizard at the War Department. At this session, Tizard briefed the British “Chain Home” radar network, then proving its worth in alerting Britain’s Fighter Command to German aircraft approaching from the English Channel or the North Sea, as well as a system known as Pipsqueak, an Identify Friend or Foe (IFF) capability under which a signal emit- Stewart Menzies, chief of Britain’s Secret Intelligence Service, MI-6 British ambassador in Washington, Philip Kerr, Lord Lothian ted by British aircraft allowed ground controllers to separate radar detections of them from those of a German aircraft.11 9 The First Americans Brigadier General Joseph Mauborgne, head of the US Army Signal Corps William Friedman, chief cryptanalyst, army Signal Intelligence Service The Genesis of a Signals Intelligence Exchange One of those in attendance at Tizard’s briefing was Brigadier General Joseph Mauborgne, head of the US Army Signal Corps, the organization which 10 contained the codebreaking SIS. Mauborgne apparently was so taken by what he had heard from Tizard that he asked for a separate meeting, which Tizard would later say was intended to have been only “a few minutes talk” but due to Mauborgne’s interest “went on until lunchtime.”12 Phelps describes the impact of the British scientist’s presentation on Mauborgne in the following way: “Tizard’s openness about IFF had so impressed General Mauborgne…that he invited Tizard to visit the Corps radar research center at Fort Monmouth, New Jersey. There Tizard was able to see for himself its SCR-268 gunlaying set.”13 A pulse radar system which was to be used to aim anti-aircraft artillery, the SCR-268 had just undergone field testing at Ogdensburg, New York, where its effectiveness at detecting aircraft proved superior to that of a network of observers which had been spread across the northern part of the state to provide visual reports. The SCR-268 also demonstrated an ability to provide the first-ever identification by a US system of an aircraft at a distance of 75 miles.14 Mauborgne may have been so taken with Tizard’s briefing that he asked the chief of the army’s SIS, Colonel Spencer Akin, and its founder and chief cryptanalyst, William Friedman, to develop a proposal for a cryptanalytic exchange with the United Kingdom. Alternatively, the Friedman proposal may have emerged from a directive by the army’s acting assistant chief of staff for intelligence, Brigadier General Sherman Miles, who had been given the task of “coordinating the details of the interchange of information covered in the [Lothian’s] Aide-memoire,” and was seeking recommendations on technologies which could be shared with the British.15 Yet another possibility is that the Akin-Friedman proposal could have been stimulated by word of talks on the parameters for the overall technical exchange then taking place in London between the American Military Observer Mission stationed there and British military leaders. At the August 31 session, army representative Brigadier General George Strong, had— apparently on his own initiative—raised with his The First Americans US Army Brigadier General Sherman Miles US Army Brigadier General George Strong British counterparts the possibility of an exchange on the cryptanalysis of German, Italian, and Japanese systems. On September 5, after the Labor Day holiday weekend, Strong cabled Generals Marshall and Miles to ask two urgent questions: “Are you prepared to exchange full information on German, Italian and Japanese code and cryptographic information therewith? Are you prepared to agree to a continuous exchange of important intercept in connection with the above?”16 Regardless of how it came to be, Akin and Friedman’s proposal appears to have been drafted for General Mauborgne at either the end of August or the beginning of September. A September 5 letter from Colonel Clyde Eastman to Mauborgne, who was then away from Washington at Fort Monmouth, seeking Mauborgne’s comments on the Strong cable, included a copy of the Akin-Friedman proposal and indicated that it had been “prepared and submitted to you several days ago.”17 Akin and Friedman began by stating that any information whatsoever about devices the United States used to encrypt its own sensitive com- munications should be off the table. They then proceeded to recommend a full exchange of cryptanalytic information with the British, “on a basis of complete reciprocity, the same [the exchange] to be on specific exchange of specific items and not upon the basis of an exchange of information of a generalized character.”18 The two further recommended exchanging training materials, information about machines used for cryptanalysis, and actual intercept, noting in the latter instance that “It would be of especial interest to us to have traffic of a tactical nature from the German, Italian, and Japanese Armies.” The only conditions suggested by the two men were (a) that as the United Kingdom currently was not at war with Japan, providing certain information about that nation might require the administration’s approval to ensure its disclosure would not affect American defense interests and (b) that the proposed cryptanalytic exchange “only be undertaken in a joint conference between the Army and the Navy on the one hand and the British on the other.” Akin and Friedman presumably suggested this latter provision in light of the fact that the two American services tended to conduct cryptanalytic activities in isolation from each other and rarely shared their methods or results.19 11 The First Americans that it support the Strong proposal as a “matter of utmost importance to National Defense.”22 Four days later, Stimson formally added “cryptanalytic information” to the categories of materials which the War Department could share with the British, with the caveat that “no information which concerns our own codes, cyphers, and methods of cryptography will be divulged.” Stimson also formally designated General Miles as the individual who would “coordinate details for the interchange of information with members of the British Technical Mission or other authorized representatives of the armed forces of the British Empire.”23 US Admiral Walter Anderson, Office of Naval Intelligence The day Strong’s telegram from London was received, Akin took it to Admiral Walter Anderson at the Office of Naval Intelligence. Anderson told Akin to inform General Miles “that the Navy’s ‘offhand’ answer to the whole project was an emphatic ‘No’ but that he would also send Miles a ‘considered answer.’ ”20 Akin and Friedman’s proposal also noted a series of objections from Commander Laurance Safford, the head of the US Navy’s cryptanalytic unit, OP-20-G. Not surprisingly, Safford agreed with the notion that discussions of the systems used by the United States to encrypt its sensitive communications should be out of bounds. However, he did not concur with the proposed “full exchange of cryptanalytic information.” He also opposed any discussions of any machines the army and navy had developed to break foreign cryptosystems and questioned the “advisability” of exchanging training material. The only thing he did not oppose outright, according to notations on the Akin-Friedman draft, was the proposed exchange of intercept.21 General Mauborgne cabled the War Department from Fort Monmouth on September 7 to urge 12 The split between the army and the navy was unchanged as of early October, when Miles wrote to Stimson that, while the army remained strongly supportive of working with the British, “the Navy Department is opposed to any exchange of information on cryptanalysis of foreign codes and ciphers.” “I understand,” Miles continued, “that this opposition is based on a fear that any information we give on our methods of cryptanalysis may aid the British in breaking down our codes and ciphers.”24 Later that month, according to historian David Alvarez, Miles, Mauborgne, and Assistant Secretary of War John McCloy—whom Stimson had hand-picked to join him at the War Department after Roosevelt had nominated him in June—“met with Stimson to review the status of the Army’s signals intelligence program and discuss cooperation with the British…. It took no time to convince him [Stimson] that the exchange project should go forward.” As a result, Stimson apparently made an on-the-spot decision to force the issue and moved quickly to do so. The same day, he met with Secretary of the Navy Knox and secured his approval. Twenty-four hours later, having obtained Secretary of State Cordell Hull’s blessing as well, Stimson approached Roosevelt, “who responded (through his military aide, General Edwin ‘Pa’ Watson) that he was happy to accept the judgment of his Secretaries of War and the Navy in this matter and approved the proposed exchange.”25 The First Americans In London, the initiative taken by General Strong at the end of August to propose a cryptanalytic exchange appears to have been met more cautiously than it was in Washington, at least in US Army circles. There were several reasons for this wariness. First and foremost, America was not yet in the war and thus perhaps not worth the risk of Britain’s disclosing its codebreaking successes, ones which for a beleaguered nation were increasingly seen as vital instruments for national survival. Moreover, the British cryptanalytic establishment saw the 1931 publication of Herbert Yardley’s The American Black Chamber, which revealed the success of the United States in reading a number of Office of Alastair Denniston, chief of Bletchley Park operation foreign diplomatic cryptosystems, as an example of Washington’s lax security practices. Finally, the Churchill offered unilaterally to Washington, “As regards Gergovernment learned through the Tizard mission man and Italian [cryptosystems], any progress we that, somewhat contrary to expectations, its defense have made is of such vital importance to us that research programs generally were significantly ahead we cannot agree at once to hand it over unreservof those of the United States. Thus, the question edly.” As for a possible visit to the United Kingdom became more one of whether America’s industrial by an American cryptanalyst, Denniston continued, might could make up for the deficiencies in Brit“Should this expert make a favorable impression, we ish capacity to produce key military technologies in could consider opening out on the Italian material, quantities sufficient to equip a modern army, navy, and possibly discuss generally ‘Y’ [wireless intercept] and air force. As a result, London would have had work problems as regards Germany, upon which no reason to think that its cryptanalytic efforts were subject their assistance might be valuable.”26 Hownot similarly ahead of the Americans’. At this point ever, the next month British and American represenin the war, moreover, London likely could not have tatives apparently reached agreement on the general perceived how the capacity of the United States to parameters of a cryptanalytic exchange and signed a mass produce cryptanalytic machinery would turn brief written statement documenting them.27 out to be as important for the war effort as, say, airContinued Progress in borne radar. It is understandable, therefore, why as late as November 1940 the chief of the Bletchley Park operation, Alastair Denniston, was arguing that, in an implicit contrast to the capabilities Tizard had Technological Cooperation As the United States and Great Britain were taking their first steps toward a discussion of cryptanalysis, their larger exchange of advanced military know-how was accelerating and, as the fall of 1940 13 The First Americans pressed into service as a troopship which also was carrying the crews who would man the first of the older destroyers being transferred by Roosevelt to the British in exchange for basing rights. Making their way first to Ottawa, the six then moved on to Washington, where they arrived on September 11.28 Alfred Loomis (r), Wall Street banker and founder of Tuxedo Park laboratory unfolded, was seen by both sides as offering ever greater potential. While there is little direct evidence on how progress in this broader technical collaboration may have influenced planning for the American cryptanalytic delegation’s visit to the United Kingdom, it seems entirely possible that it both solidified the support of senior leaders such as Stimson for a cryptanalytic exchange with the British and raised American expectations with regard to what the British codebreakers could offer. Moreover, the willingness of the British to share many of their most advanced technologies with the Americans may have incentivized the Americans to reciprocate by providing the machine which the SIS had developed to crack Purple. On September 6, 1940, the remaining six members of the Tizard mission—a combination of leading scientists and military officers familiar with the operational use of the technologies the team would show to the Americans—arrived in Halifax, Nova Scotia, on the Duchess of Richmond, an ocean liner 14 That evening was one of the most pivotal moments in the history of Anglo-American scientific cooperation during World War II. Each of the two future allies had made progress in radar technologies, with the British further along in terms of both the precision and range at which their systems could detect enemy aircraft. Given the urgency created by the outbreak of hostilities in Europe, the British also had succeeded in moving radar out of their research laboratories to create an operational network which stretched across the south and east of England and, as described by Tizard to American military leaders, aided greatly in the successful defense mounted by the Royal Air Force against the Luftwaffe during the Battle of Britain. That engagement, however, prompted a realization that, while ground-based systems could provide early warning of aircraft approaching the British coastline, they were limited in what they could do to vector RAF interceptors to their targets under combat conditions. For that, a device was needed which was small enough in size and weight to be mounted in an aircraft yet at the same time powerful enough to generate radio waves of sufficiently short length to avoid the problem created by longer ones, which was that the latter’s “strong … echo from the ground obscured the weak echo from an aircraft beyond a certain range.” 29 However, the British had surmounted this challenge. Early in 1940, a group of scientists at the The First Americans University of Birmingham successfully tested a prototype of a device known as the cavity magnetron, which was both small and powerful enough to meet the requirements of an effective mobile air-based radar system. The Tizard mission brought one of the early versions of the magnetron to the United States. On that pivotal evening of September 11, it was demonstrated to a small group of American scientists and military officers who had been assembled at Washington’s Wardman Park Hotel by Alfred Loomis. Loomis, a Wall Street banker whose fortune had escaped the ravages of the Great Depression, was a talented amateur scientist who ran a private laboratory at Tuxedo Park, an enclave for the wealthy located in the Ramapo Mountains north of New York City. Among the many projects Loomis worked on there, in the company of some of the most prominent American scientists of the time, were microwave systems.30 Loomis immediately grasped the revolutionary potential of the cavity magnetron. Accordingly, he invited the two members of the British delegation most familiar with the device, the physicists Edward Bowen and John Cockcroft, to visit Tuxedo Park. Once there, Bowen and Cockcroft provided a demonstration of the magnetron which awed and delighted the American scientists, no one less so than Loomis himself. As Bowen and Cockcroft had brought the blueprints for the device, Loomis quickly gathered representatives of America’s leading electronic manufacturers and placed large orders for it. By the middle of October, he also had sealed an agreement with the Massachusetts Institute of Technology for the establishment of a new radar laboratory that would become known as the “Rad Lab” and serve as the key locus for Allied research and development projects in this field for the remainder of the war. The magnetron was not the only technology which members of the Tizard mission brought with them to the United States, but it was by far the most important and the most far reaching in terms of its impact on the tightening of Frank Rowlett, US Army Signal Intelligence Service cryptanalyst Anglo-American scientific ties and, ultimately, the Allies’ conduct of the war.31 One individual Loomis was quick to share his excitement with was Secretary of War Stimson, who was his first cousin on his mother’s side. Traveling to Washington a few days after the British had demonstrated the magnetron at Tuxedo Park, Loomis met with Stimson and General Marshall at the War Department and also had dinner with Stimson at the latter’s home that evening, to which Stimson also had invited some of his key aides, including John McCloy. Of the meeting at the War Department, Stimson would write: Alfred Loomis came in in the afternoon, full of excitement over his interviews with the British and with the scientists, and he was full of the benefits that we were getting out of the frank disclosure by the British to us of their inventions and discoveries of methods they have made since the war. He said we were getting the chance to start now two years ahead of where we were…. 15 The First Americans Loomis, Stimson also would note, “said that our [the War Department’s] frankness had enabled the British to put their hands on the table and had given us a rich mine of information and it has also brought the Navy around to a better state of frankness on their part.”32 Around the same time, Stimson, Marshall, and McCloy were receiving briefings on a separate technological wonder, only this time it was an American one. In the weeks following the telegram from General Strong in London that recommended a cryptanalytic exchange between the United States and Great Britain, the SIS finally, after more than eighteen months of work, had succeeded in breaking Purple. The key breakthrough, according to William Friedman, had come on September 20 with the first two fully decrypted Japanese diplomatic cables produced on September 27.33 Along with SIS cryptanalyst Frank Rowlett, who had played a key role in breaking the Japanese cryptosystem, Friedman and SIS chief Akin immediately briefed their success to General Mauborgne, the Signal Corps commander. Mauborgne quickly informed General Miles, the army G-2, while Friedman notified OP-20-G head Safford.34 Sometime thereafter, Akin asked Rowlett to prepare a demonstration for “an important official of the War Department,” not indicating who that official was. According to Rowlett, “about a week later” Akin indicated that the visit would take place the following afte