Jørgen Veisdal in Cantor’s Paradise:
It is the beginning of November, 1943. The Manhattan project is in its fourth year of operations, and J. Robert Oppenheimer’s Los Alamos Laboratory is eleven months into its mission of designing and building the first atomic bomb. Oppenheimer had in 1942 been headhunted to the project by its Director, Lieutenant General Leslie Groves (1896–1970) on the strength of the recommendation of physicist Arthur Compton (1892–1962). He was 39 years old at the time, and came to the project already a Professor of Physics at the University of California, Berkeley. There, starting in the mid 1930s he had worked on deuteron-induced nuclear reactions, the so-called Oppenheimer-Phillips process, whose experiments were conducted at the newly built UC Berkeley cyclotron.
Although a classified endeavor, it was not uncommon for scientists and engineers on the project to communicate between themselves in letter-form about how things were proceeding. Indeed, communication across both institutions and scientific branches was imperative for ensuring a successful “Project Y”. Classified, of course, many such letters have since been made available to the public. When reading through Oppenheimer’s communications, one in particular stands out.