Nuclear surveillance is meant to include atomic weapons State secrets without consent from other states (espionage). In the past, of nuclear weapons and many alleged or supposed spying cases, there have been many cases of known nuclear espionage. Since nuclear arms are customarily considered one of the most critical state secrets, all nuclear weapons countries have stringent limits on details about the design, handling, distribution, and deployment of atomic weapons. State right to disclose nuclear weapons information by non-proliferation arrangements is also limited.

The Manhattan Project
For the Manhattan Project, safety was a way of life. The intention was to keep Germany and Japan secret regarding the whole nuclear bomb program. Safety officials of the Manhattan Project succeeded in that.

However, they have managed to avoid the Soviet Union being informed of the atomic bomb. In the war against Germany, the Soviet Union remained a brutal regime and a possible future enemy, even as an alliance between Britain and the US. Security officials have been less effective here. In Los Alamos and many other sites, Soviet spies also infiltrated the Manhattan Project, sending crucial information to Russia that helped speed up the production of the Soviet bomb.

During the war, two types of nuclear bombs were produced simultaneously: a comparatively short fission weapon and an implosive atomic weapon of a greater variety. The Thin Man-type gun design was not feasible with plutonium, so a basic weapons-type named Little Boy, uranium-235, an isotope that only represents 0.7% of natural uranium, were made.

Since uranium-238 was the chemically equivalent one and had about the same density, it didn't prove easy to distinguish the two. Uranium enrichment was carried out using three methods: electromagnetic, gas, and thermal. They undertook most of the testing at the Oak Ridge, Tennessee Clinton Engineering Works.

Parallel to uranium, researchers at the University of California in Berkeley found in 1940 an attempt to manufacture plutonium. The Chicago Pile-1 artificial reactor, demonstrated in 1942 by the University of Chicago Metallurgical Laboratory, constructed the X-10 graphite reactor at Oak Ridge and the manufacturing reactors at Washington's Hanford plant which uranium was irradiated and transformed into plutonium. Plutonium was isolated from the uranium by the method of bismuth phosphate. The implosion weapons Fat Man were developed by the Los Alamos Laboratory in a collaborative design and production effort.

Intelligence on the German nuclear bomb program was also responsible for the project. Manhattan Project workers worked in Europe during Operation Alsos, often under enemy lines, gathering radioactive materials and papers, and rounding up German scientists. Despite the stringent secrecy of the Manhattan program, Soviet nuclear spies could infiltrate the scheme successfully. At the Trinité drill, conducted at the Alamogordo Bombing and Gunnery Range in New Mexico, the first atomic weapon ever detonated was an implosion-like bomb on 16 July 1945. A month later, they used explosives from Little Boy and Fat Man in the Hiroshima and Nagasaki atomic bombing with Manhattan Project employees as bombing engineers and weapons on the bomb attack aircraft, respectively.

In the near post-war years, in the Bikini Atoll, the Manhattan Project carried out weapons tests, developed experimental weapons, encouraged creating a national laboratory network, funded medical radiologic sciences, and laid the groundwork for the nuclear navy. The project was initiated in Operation Crossroads. It continued to regulate American atomic weapons research and manufacture until the United States Atomic Energy Commission was established in January 1947.

Following the bombings in Hiroshima and Nagasaki, a group of physicists from the Manhattan project formed the Atomic Scientists' Bulletin, which was initiated as an emergency intervention by scientists who thought there had to be an urgent educational program in nuclear arms. In a June 1946 speech to UNAEC, the Baruch Plan recommended that an international atomic production authority be established, but was not approved. The plan was not implemented in 1946.