The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada.

From 1942 to 1946, the project was directed by Major General Leslie Groves of the U.S. Army Corps of Engineers. Nuclear physicist J. Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the bombs. The Army program was designated the Manhattan District, as its first headquarters were in Manhattan; the name gradually superseded the official codename, Development of Substitute Materials, for the entire project. The project absorbed its earlier British counterpart, Tube Alloys, and subsumed the program from the American civilian Office of Scientific Research and Development.

The Manhattan Project employed nearly 130,000 people at its peak and cost nearly US$2 billion (equivalent to about $27 billion in 2023). The project pursued both highly enriched uranium and plutonium as fuel for nuclear weapons. Over 80 percent of project cost was for building and operating the fissile material production plants. Enriched uranium was produced at Clinton Engineer Works in Tennessee.

Sir Joseph Rotblat (4 November 1908 – 31 August 2005) was a Polish and British physicist. During World War II he worked on Tube Alloys and the Manhattan Project, but left the Los Alamos Laboratory on grounds of conscience after it became clear to him in 1944 that Germany had ceased development of an atomic bomb.

His work on nuclear fallout was a major contribution toward the ratification of the 1963 Partial Nuclear Test Ban Treaty. A signatory of the 1955 Russell–Einstein Manifesto, he was secretary-general of the Pugwash Conferences on Science and World Affairs from their founding until 1973 and shared, with the Pugwash Conferences, the 1995 Nobel Peace Prize "for efforts to diminish the part played by nuclear arms in international affairs and, in the longer run, to eliminate such arms."

Early life

Józef Rotblat was born on 4 November 1908 to a Polish-Jewish family in Warsaw, then part of the Russian-ruled Kingdom of Poland, better known as Congress Poland. He was one of seven children, two of whom died in infancy. His father, Zygmunt Rotblat, built up and ran a nationwide horse-drawn carriage business, owned land and bred horses. Józef's early years were spent in what was a prosperous household but circumstances changed at the outbreak of World War I. Borders were closed and the family's horses were requisitioned, leading to the failure of the business and poverty for their family. Despite having a religious background, by the age of ten, he doubted the existence of God, and later became an agnostic.

Rotblat's parents could not afford to send him to a gymnasium, so Rotblat received his secondary education in a cheder taught by a local rabbi. He then attended a technical school, where he studied electrical engineering, graduating with his diploma in 1923 in the newly established Republic of Poland.