Los Alamos and the British Mission

A partnership between countries that endures today

By Angie Piccolo | October 10, 2023

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William Penney, Otto Frisch, Rudolph Peierls, and John Cockcroft were four members of the British Mission that worked alongside American scientists and engineers on the Manhattan Project during World War II.

After 27 months of grueling hours and scientific secrecy amidst the pressure of a mounting death toll and Nazi Germany’s own weapons development, the race to create an atomic bomb had come to an end. It was time to celebrate.

On September 22, 1945, scientists, engineers, and their families gathered downtown at Fuller Lodge to celebrate the success of the Los Alamos atomic bombs and the end of World War II.

The party was hosted by members of the British Mission and their wives and included food, dancing, and a satirical play based on the lighter moments of wartime life in Los Alamos. However, this party was more than just entertainment and a night of festivities; it also represented a partnership between countries that endures today. 

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This invitation to a “Birth of the Atomic Era” party hosted by members of the British Mission and their families is part of the collections of the Lab’s National Security Research Center. 

What was the British Mission? 

The British Mission was made up of some of Europe’s best experimental and theoretical physicists as well as experts in electronics and explosives. They worked alongside American scientists during the U.S. government’s top-secret Manhattan Project to create an atomic bomb in a perceived race against Nazi Germany. This group of scientists included Nobel laureates James Chadwick and Niels Bohr; future 

Nobel laureate Joseph Rotblat; and Klaus Fuchs, later confirmed to be a spy who provided Russia with secret nuclear information.

Were they all from Great Britain?

Fifteen members of the British Mission were British nationals, including William Penney, Ernest Titterton, and James Tuck. NSRC senior historian Alan Carr explains in his article “Remembering the British Mission” that some “. . . members of the British Mission fled to Britain to escape the persecution of Jews and the Nazi regime.” These refugees included Niels Bohr and his son Aage from Denmark; Boris Davison from Russia; Otto Frisch from Austria; Klaus Fuchs and Rudolf Peierls from Germany; and Joseph Rotblat from Poland.

Historic U.S.-U.K. Partnership

The science of atomic weapons began with the discovery of nuclear fission in Europe in 1939. British research related to the development of a nuclear bomb accelerated in 1940 after scientists Rudolf Peierls and Otto Frisch wrote a memorandum indicating the need for only a small amount of uranium to produce a weapon, according to Dennis C. Fakley in “The British Mission.”

Fakley’s article also explains that the memorandum was sent to Britain’s newly established MAUD Committee, which developed its own reports confirming the feasibility of an atomic bomb. These reports were shared with the United States, which at first was not as committed to nuclear research as the United Kingdom. 

This changed with Japan’s attack on Pearl Harbor in December of 1941 and the United States’ entrance into World War II. The U.S. began its own separate research and was less willing to share information with the U.K. because of concerns over what the British would do commercially after the war, according to the NSRC documentary Trinity and the British Mission. 

The documentary explains how the U.S. quickly surpassed the U.K. in research given its vast resources and the geographic advantage of being far from the battlefields. U.K. Prime Minister Winston Churchill and U.S. President Franklin D. Roosevelt signed the Quebec Agreement in 1943, which cemented Britain’s collaborative, albeit secondary, role in the research and development of atomic weapons with the United States. Members of the British Mission began arriving in the United States soon after. 

What did the British Mission contribute to the Manhattan Project?

The British Mission made up a very small portion (only 19 individuals) of the scientific community at Los Alamos, but “their small numbers belie their importance to the mission of the wartime lab,” said NSRC historian Nic Lewis.

According to Lewis, members of the British Mission “brought their expertise in several key areas, including explosives and hydrodynamics. James Tuck, for example, helped to develop the shaped explosive lenses for the implosion weapon and Rudolf Peierls used his experience with airborne blast waves to contribute to numerical solutions to hydrodynamic problems.” 

Meanwhile, William Penney, the post-World War II leader of the British nuclear weapons program, “calculated the height at which the atomic bombs should be dropped over Japan, and worked with [Los Alamos scientist and future Nobel laureate] Luis Alvarez to predict the damage effects of the blast waves.” 

Author Ferenc Szasz writes in British Scientists and the Manhattan Project that other members of the British Mission took on important positions at Los Alamos by leading various groups. This included Otto Frisch leading the Critical Assemblies group, Egon Bretscher leading the Super Experiments group, and George Placzeck taking charge of the Composite Weapons group. Although James Chadwick remained in Washington, DC, during the war, he contributed to the success of the Manhattan Project through his diplomatic efforts toward developing a strong bond with U.S. Army General Leslie Groves, head of the Manhattan Project, and maintaining good relations between the two nations.

After World War II, the Atomic Energy Commission, a civilian-controlled federal agency and precursor to the Department of Energy, took over operations at Los Alamos.

Classified information regarding nuclear weapons research and development was no longer shared with foreign countries, including Britain. As such, British Mission scientists were no longer even allowed access to their own reports.

Everett Titterton was the last of the British Mission members to leave the Lab, on April 12, 1947, and it wasn’t until the signing of the Mutual Defense Agreement in 1958 that the U.S. and the U.K. began sharing information again, according to Carr’s “Remembering the British Mission.”

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The Manhattan District requested that leading scientists and engineers from the Manhattan Project fill out questionnaires. These records now provide important details about the contributions made by members of the British Mission during the Manhattan Project.


The British Mission Reports Collection

The National Security Research Center (NSRC) houses the British Mission Reports Collection, which includes documents, memos, and research created by members of the British Mission; the collection highlights their experimental findings, investigations, and developments in nuclear science during the Manhattan Project. 

According to NSRC archivist Danny Alcazar, this unclassified collection is significant because it covers British research not only during World War II but also before U.S. entry into the war and demonstrates how British scientists’ discoveries contributed to the Manhattan Project and the creation of the atomic bomb.

Special thanks to NSRC archivist Sara Boteler for research assistance for this article.

Watch the NSRC Documentary Trinity and the British Mission

Packed with archival footage, this NSRC-produced documentary illuminates the complex collaboration between scientists of the Manhattan Project and the British Mission. The film also traces the evolution of the partnership between the two countries from the end of the war to the present day.

Trinity and the British Mission is narrated by the NSRC’s senior historian Alan Carr and features interviews with senior scientists at Los Alamos, including Mark Chadwick, Marianne Francois, and U.K. Atomic Weapons Establishment historian Richard Moore.