Milestones of Innovation 4: The Letter That Led to the Atomic Bomb


Crisp statements of a case to a prepared, if skeptical, mind have often changed the history of innovation. Perhaps the most critical example of this in the 20th Century is the memorandum that reached Sir Henry Tizard, chief scientific advisor to Britain’s Air Ministry, 75 years ago today, on the 19th of March, 1940. This document, signed by refugee physicists Otto Frisch and Rudolph Peierls, thrust open a contentious transatlantic path to President Franklin Roosevelt’s decision in October 1941 to launch an all-out program to beat Hitler to an atomic bomb.

The way that Peierls and Frisch framed the issues crystallized the fears that had swirled among the world’s nuclear physicists for more than a year.  The possibility of a bomb arose as soon as two chemists in Berlin, Otto Hahn and Fritz Strassman, discovered in December 1938 that uranium atoms could split, or fission, into roughly equal halves. This unexpected process released an immense amount of energy along with surplus neutrons to keep a chain reaction going. Frisch, with his aunt Lise Meitner (formerly Hahn’s colleague), had promptly published the first interpretation of the findings, including the name, fission.

Many had hoped that an atomic explosive would not be practical. But now, Tizard read the few typed pages transmitted to him by a feisty Australian physicist named Mark Oliphant, who had found jobs in his University of Birmingham lab for both Peierls, a Berliner, and Frisch, a Viennese. They had both fled Germany in 1933, when Hitler came to power. Looking at the issues in a new light, the two asserted that an atomic bomb was possible if you could 1) build a factory to separate just a few pounds of pure uranium 235, a rare isotope of uranium; 2) suddenly jam together a “critical mass” of it; and 3) confine it just long enough to produce an explosion equivalent to a thousand or more tons of TNT. They said the uranium 235 bomb would annihilate defenses, kill thousands of people, and bathe a vast area with lethal radioactivity.

Peierls had been in England for seven years. Frisch had started out in England before spending five years in the world-famous physicist Niels Bohr’s institute in Copenhagen. Good fortune brought him to Mark Oliphant’s lab at Birmingham shortly before Hitler’s tanks and dive-bombers smashed into Poland on Sep. 1, 1939. As citizens of Hitler’s Reich, the two were barred from war work despite their expertise.

Reading their words, Tizard at once contacted a leading physicist, G.P. Thomson, and instructed him to form a committee to test the assumptions Frisch and Peierls had stated so starkly. The committee began meeting in April 1940 and granted modest sums to research groups in Oxford, Cambridge, Birmingham, and Liverpool. Soon, Frisch and Peierls protested being cut off from their own work and were brought in as consultants.

To solve the central problem—separating uranium 235 from the much more abundant uranium 238—Frisch suggested recruiting refugee, Franz Simon of Oxford, who had already started exploring how to press a uranium gas, uranium hexafluoride, through ultra-fine metal membranes. The resulting lighter gas, uranium 235 hexafluoride, could gradually be “enriched” in a cascade of thousands of stages. The British committee managed to keep everyone talking freely to each other, summarizing conclusions clearly after frequent meetings.

The committee sent its minutes faithfully across the Atlantic to a corresponding group in America. That U.S. committee had been set up after Einstein’s famous letter to President Roosevelt in the fall of 1939 (the letter warned that uranium could split with a huge release of energy, that the discovery had been made in Germany, and that the Germans were showing acute interest in uranium supplies), but its chairman simply locked the British reports in his safe. Compounding the problem was the unfamiliarity of the two top U.S. war science bosses, engineer Vannevar Bush and chemist James Conant, with nuclear physics. Finally, in the summer of 1941, Conant was told in stark terms of a bomb that could obliterate a city—and that Hitler might get it first. Shortly thereafter, a Harvard chemist whom Conant trusted, George Kistiakowsky, told him after studying the matter that he was “100 percent sold” the bomb would work. Frisch and Peierls’ point was finally getting action.

Moving swiftly now, Bush took the matter to Roosevelt on Oct. 9, 1941. The President seized control instantly. Seeming to take the decision for a crash program for granted, FDR focused on postwar control and securing a good supply of uranium. He would find the money.

Less than three years after the table top discovery of fission in Berlin, the U.S. actions paved the way to beating Hitler to the bomb, and the world was on its way into the nuclear age.

[Editor’s Note: This is the fourth of an envisioned series of notes about major anniversaries in innovation and what they teach us. You’re invited to suggest other milestones of innovation for in the Xconomy Forum. Example: This year will mark the 150th anniversary of Alexander Holley’s pilot plant in Troy, New York, for making steel by the Bessemer process.]

Further Reading:

Jeremy Bernstein, “A Memorandum that Changed the World,” American Journal of Physics, Volume 79 (number 5, May 2011), pages 440-446.

Richard Rhodes, The Making of the Atomic Bomb, Simon and Schuster, 1986 ISBN 0-671-44133-7.

Margaret Gowing, Britain and Atomic Energy, New York, St. Martin’s Press, 1965.

Xconomist and science reporter Victor McElheny of MIT is author of Watson and DNA: Making a Scientific Revolution (2003) and Drawing the Map of Life: Inside the Human Genome Project (2010) Follow @

Trending on Xconomy