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Historical Events
Historical Events | Aug. 20, 2021

The International Agreements

The literature on cryptology in World War II initially emphasized the close cooperation between the United States and the United Kingdom during the war, with little attention to any disagreements or controversies. Some recent books have called more attention to conflicts occurring within this special relationship.

The disputes center around two main points: first, complaints that there has not been sufficient public acknowledgment of the important role British cryptanalysts had in breaking Japanese systems. A second area of controversy is the claim that naval officials in both the United States and the United Kingdom believed the other side was not sharing COMINT and related materials as required by the bilateral agreement and were considering the severance of relations.

Given that the United States and Great Britain are nations with different political, military, social -- and cryptologic -- traditions, and had slightly different war aims, it is not surprising that the official relationship was marked by problems and disagreements, and, even at times, rivalries. However, it seems that serious dissatisfactions in World War II were limited to a few officers on both sides. Cryptologic cooperation survived -- and thrived -- because those at the top found that it served national interests and those at the working level formed close and productive relationships with their colleagues.

It should be remembered that at the time it was unusual for two countries to cooperate as closely as the U.S. and UK did in such a sensitive endeavor as Communications Intelligence. Nevertheless, the U.S. and the UK shared not only product but also techniques in all facets of the COMINT process.

It is true that the role of the United Kingdom in collecting and solving Japanese cryptosystems has been underemphasized. The Center for Cryptologic History believes the UK contribution to the common struggle against Japan should receive more attention from scholars and journalists.

For the purposes of the present series, however, we must content ourselves with the story of how cooperation came about and its immediate effects.

Throughout the 1920s and 1930s, the British built upon their cryptanalytic successes in the First World War. The principal organization became the Government Code and Cipher School (GC&CS).

In 1938, GC&CS moved into its wartime headquarters, Bletchley Park, about 60 miles north of London. BP or The Park, as it was familiarly known, had been the estate of a London stockbroker named Herbert Leon, who constructed a large mansion on the grounds. Sir Herbert died in 1926 and his widow in 1937; after her death, the mansion and its extensive grounds were prepared for sale, with plans to subdivide the grounds into smaller housing plots.

However, GC&CS acquired the property instead and transferred its operations to the estate. BP had a number of advantages, the primary one being excellent railroad communications in all directions but especially with London. It was also located relatively close to Oxford and Cambridge. GC&CS began erecting a number of "temporary" huts on the grounds to house its cryptanalytic activities.

To exploit enemy communications, GC&CS recruited many of the finest minds in the UK, mathematicians, puzzle experts, engineers, and linguists. Bletchley Park was once described as "a bad place to play chess for money."

Although the main British effort was against German communications, as might be expected, the British had done considerable analysis of Japanese messages as well. Most of the work prior to the outbreak of war in Asia was done in the field. Once war broke out, BP greatly increased the number of analysts, and instituted a high quality training program for translators of military Japanese, employing a retired Navy captain, Oswald Tuck, with extensive Asian experience.

World War II began in 1936 with the Japanese invasion of China. In Europe the war was sparked in late 1939 by the German invasion of Poland. Great Britain and France, which by treaty had agreed to come to Poland's defense should Hitler attack, found themselves at war with Germany.

The first years of the war went badly for the Allies. The Axis Powers seemed to be succeeding in whatever they sought -- Germany conquering much of Europe, Italy the same in North Africa, and Japan ditto in mainland Asia.

In the west, Great Britain was at war with Germany, but was on the defensive; most other countries in western Europe had fallen to the Nazis. It was in Britain's interest for the United States to enter the war, or, failing that, to provide as much support as possible.

The United States, however, was not ready for war, either materially or psychologically. The evils of Nazism and the dangers of Japanese militarism were evident to the public and leadership, but many in the U.S. still hoped to avoid going to war. America's senior leadership was also worried, knowing that if war came, the country was not prepared -- the military was small and lacked adequate equipment and training.

Some in the leadership, starting with President Franklin Roosevelt, advocated support to Great Britain in its struggle against Nazi Germany, recognizing also that British survival and British victory were vital to American security. With the blessing of FDR and Prime Minister Churchill, some limited exchanges of military information were conducted between the two nations.

On August 31, 1940, during a meeting in London between U.S. Army and Navy representatives with the British Chiefs of Staff, the American Army delegate, Brigadier General George Strong, Chief of the War Plans Division, suggested that the time had come to share intelligence information between the two countries, including data on cryptanalysis. Strong gave a short statement about U.S. Army progress against Japanese and Italian systems. The U.S. Navy delegate, Rear Admiral Robert Ghormley, Assistant CNO, said nothing about his service's cryptanalytic capabilities. The British side only promised to consult with the Prime Minister about the topic.

Within a week the British came back with a positive reply. This time both Strong and Ghormley sent requests to their service chiefs for permission for a full exchange of cryptanalytic information.

Over the next few weeks, the issue was discussed at the staff level, with few results. Secretary of War Stimson took up the matter with Navy Secretary Frank Knox in late October, again with indifferent results. Stimson, in particular, was enthusiastic about the bilateral sharing of this secret information and put his staff to work on it; he also sought agreement from the White House and the Secretary of State. On October 24, Roosevelt's military aide notified Stimson that the president approved.

By December, military authorities in the U.S. and Great Britain agreed to share cryptanalytic information with each other. It was also decided to send a U.S. delegation to Britain to begin the official exchanges.

The original intention had been to send the delegation under the leadership of William Friedman, who had strong credentials as a cryptologist and was well-known to the British. Unfortunately, however, Friedman took seriously ill, required hospitalization and rest, and was unable to undertake international travel under wartime conditions.

Instead, the Army representatives were Captain Abraham Sinkov, who had been engaged in cryptanalysis under Friedman since 1930, and Lieutenant Leo Rosen.

Chosen as the Navy representative on the delegation were Lt Robert Weeks and Lt(j.g.) Prescott Currier. Lt. Weeks was a communications officer assigned to OP-20-G.

Currier had been trained as an intercept operator in an early class of the On The Roof Gang. When his enlistment expired, he left the service and enrolled in George Washington University. He was also commissioned an ensign in the Naval Reserve and came back to OP-20-G as an officer.

In addition to information on American cryptanalysis, the officers took gifts for the British, including one of the analog machines for PURPLE, the Japanese diplomatic messages, and a RIP-5 kana typewriter.

Officers and gifts departed from Annapolis on the H.M.S. King George on January 24, 1941; the ship joined a convoy carrying beef from Argentina to England. Because convoys had to take special measures to avoid German battleships and submarines, the trip took about two weeks to reach the British naval base at Scapa Flow.

Originally, the delegation was to leave the Orkney Islands by flying boat, but it was discovered that the crates of U.S. equipment would not fit in the aircraft. The material instead was lashed to the deck of a cruiser.

Not long after the convoy started, the cruiser came under German attack. The Americans were instructed to don Mae West vests and heavy clothing, which would increase their survival time in the North Sea from four minutes to six. As Currier later remembered, after a number of bombs had exploded, "I heard what sounded like a large chain being dragged fore and aft along the deck; someone said that we were being strafed."

As it turned out, the crates of equipment came through undamaged; the Germans had used anti-personnel ammunition instead of rounds with more penetrating power.

Back on land, after a ride in a truck convoy under black-out conditions to Bletchley Park, the American delegation was introduced to Commander Alastair Denniston, Chief of the Government Code and Cipher School, and his staff.

The American delegation was given free access to all areas of Bletchley Park, freedom to talk with anyone, and the opportunity to take whatever notes were wanted. Over the course of the visit, the Americans were shown all operations and given field trips to other COMINT stations. U.S. Army and Navy personnel split up, the better to work with their British service counterparts.

The only area where the Americans did not get cooperation was from their own personnel. Currier and Weeks had orders directing them to report to the Naval Attache at the U.S. Embassy in London for "administrative purposes." Try as he might, the Naval Attache could not get Currier or Weeks to divulge their mission, and they left the embassy under threat of a court martial.

The Americans got another reminder of the nearness of the war during a visit to an underground command headquarters in Dover Castle. Radar screens showed German bombers taking off from a base in occupied France. When they went topside, where they saw the contrails of the German bombers in the sky, joined shortly by the contrails of British fighters from Dover. As Currier recalled, "the contrails merged and turned and looped around each other and after a brief encounter the bombers turned back toward France."

For its return, the American delegation sailed to Nova Scotia, where a U.S. destroyer met them. The delegation and its equipment went next to the Washington Navy Yard.

The Sinkov-Currier mission actually had accomplished a great deal in advancing U.S.-UK cryptologic relations. They were shown virtually the entire British COMINT system, from collection sites to cryptanalytic processes, including extensive touring of the work at Bletchley Park. The Americans were presented with a new type of DF equipment to take home with them. With their gift of a PURPLE ANALOG and some other materials to GC&CS, the Americans were able to assist the British wartime effort.

If there were later dissatisfactions with the results of this first contact, they were, perhaps, inherent in the nature of the delegation. It was junior in rank: American captains and lieutenants were sent to deal with senior British military and civilian officers. The delegation also had not been given adequate briefings on what U.S. organizations wanted them to get out of the visit, or what they should expect to see.

The U.S.-UK cooperation began early -- even before the United States was a combatant in the war -- and grew closer during the war. Over the course of the war, the U.S. Army and Navy concluded separate COMINT agreements and conducted individual COMINT relations with their British counterparts.

In February 1941, U.S. and UK COMINT representatives conferred in Singapore on their mutual progress and problems, and met again in April in Manila. They shared information directly and made arrangements for continued sharing.

The secret U.S.-UK cryptologic relationship closely resembled the well-publicized bilateral military cooperation. Behind official amity, some disagreement and bickering occurred about policy and procedure, and, in fact, some personnel on both sides felt the other had not been as forthcoming as promised. At the working level, however, cryptanalysts got along quite well and had great success in exploiting the communications of their common enemies.

The results, however, answer the criticism. The U.S.-UK cooperative successes in cryptology shortened the war in all theater of fighting by many months and saved the lives of untold thousands of Allied troops.



  • Robert L. Benson, A History of U.S. Communications Intelligence During World War II: Policy and Administration (Center for Cryptologic History, 1997), pp. 20-21.
  • Prescott Currier, "The First United States Contact with the British COMINT Organization," NCVA (Paducah, Ky.: Turner Publishing Company, 1996), pp. 32-35.
  • Micahel Loewe, "Japanese Naval Codes," in F. H. Hinsley and Alan Stripp, eds., Codebreakers: the Inside Story of Bletchley Park (Oxford University Press, 1993).
  • Albert Pelletier, "Cryptography -- Target Japan," NCVA (Paducah, Ky.: Turner Publishing Company, 1996), pp. 27-32.
  • Bradley F. Smith, The ULTRA-MAGIC Deals and the Most Secret Special Relationship (Novata, CA: Presidio Press, 1993).
  • Alan Stripp, Codebreaker in the Far East (London: Frank Cass, 1989).
  • Bob Watson, "How the Bletchley Park buildings took shape," in F. H. Hinsley and Alan Stripp, eds., Codebreakers: the Inside Story of Bletchley Park (Oxford University Press, 1993).



Bletchley Park was saved from the bulldozers in the 1990s, and now is open to the public two weekends a month. The "temporary" huts still stand on the grounds. "The Park" is a great place to visit -- it's easily accessible by railway from London; if a trip to the estate is not possible, BP has a good site on the WWW.