Scientific Collaborations during World War

Question

Nowadays, scientific progress is often based on very big collaborations, like the discovery of gravitational waves by the Ligo and Virgo collaborations. But also in many other branches of science, like mathematics, there has always been a big exchange of scientists from all parts of the world working in the same field. I am just curious, how was the situation during the world wars, especially World War II?

Hence, I would like to start a "big-list", where everyone is welcome to answer with an example of some big or small collaboration involving scientists from different countries during this time and some progresses achieved therein.

Answer 1

The most famous example of a collaboration between scientists/mathematicians during World War 2 is the Government Code and Cypher School (GC&CS), an intelligence organisation which had the task of decrypting secret communications of the Axis Powers. The intelligence obtained was termed as "Ultra".

During the Second World War, GC&CS was based largely at Bletchley Park, in present-day Milton Keynes, working on understanding the German Enigma machine and Lorenz ciphers. In 1940, GC&CS was working on the diplomatic codes and ciphers of 26 countries, tackling over 150 diplomatic cryptosystems. Senior staff included Alastair Denniston, Oliver Strachey, Dilly Knox, John Tiltman, Edward Travis, Ernst Fetterlein, Josh Cooper, Donald Michie, Alan Turing, Gordon Welchman, Joan Clarke, Max Newman, William Tutte, I. J. (Jack) Good, Peter Calvocoressi and Hugh Foss.

Apart from the famous British mathematicians like Alan Turing and Gordon Welchman mentioned above, mathematicians from different countries (mainly the Allies) were also directly or indirectly involved in the work at Bletchley Park. A few notable among them are Marian Rejewski (Polish) and Solomon Kullback (American). In fact, it was Rejewski and his fellow Polish mathematicians who first cracked the Enigma cipher. Welchman in his book The Hut Six Story: Breaking the Enigma Codes has written, "Hut 6 Ultra would never have gotten off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military version of the commercial Enigma machine, and of the operating procedures that were in use."

The collaboration was a success and it is even mentioned on Wikipedia that:

Many commentators say the flow of Ultra communications intelligence from the decryption of Enigma, Lorenz, and other ciphers, shortened the war substantially, and might even have altered its outcome.

After the Second World War, in June 1946, GC&CS was renamed the Government Communications Headquarters. However, the work which was done at Bletchley Park remained a secret for a long time after the war!