Mark 21 nuclear bomb
The Mark 21 nuclear bomb was a United States nuclear gravity bomb first produced in 1955. It was based on the TX-21 "Shrimp" prototype that had been detonated during the Castle Bravo test in March 1954. While most of the Operation Castle tests were intended to evaluate weapons intended for immediate stockpile, or which were already available for use as part of the Emergency Capability Program, Castle Bravo was intended to test a design which would drastically reduce the size and costs of the first generation of air-droppable atomic weapons (the Mk 14, Mk 17 & Mk 24). At long, in diameter, and weighing , the Mk-21 was half the length and one-third the weight of the Mk-17/24 weapons it replaced. Its minimum yield was specified at four megatons.
Project GABRIEL
During the Cold War era, there was an escalation of the atmosphere testing of nuclear weapons. After the atomic bomb in 1945, testing continued and the scale increased with the first hydrogen bomb in 1952. Soon after the United States tested the hydrogen bomb, the USSR followed, in 1953. The mushroom clouds that occurred from the explosions released radioactive isotopes in mass quantities.
The first comprehensive study of this problem began in spring 1949 with a one-man project called GABRIEL, conducted by Nicholas M. Smith Jr. at Oak Ridge National Laboratory. Smith produced his first report in 1949. Project GABRIEL was revived in mid-1951 because bombs that were dropped had brought up concerns people had about the dangers of strontium-90. United States Atomic Energy Commission (AEC) was interested by GABRIEL's report though they said it was lacking in hard data and needed independent confirmation of the tests.
After reviewing Project GABRIEL in 1953, it was given first priority status. The secret project would define "practical limits" for using atomic weapons. A task team was assembled and the codename used was "Project HORN." In 1954, AEC argued that fallout was harmless because there wasn't enough evidence to prove that fallout would harm humans, animals, or crops. The AEC campaign persuaded the public that the worldwide fallout was harmless. This claim was later disputed when scientists announced publicly that there was no safe level of radiation. This was confirmed in a confidential report by a geneticist for the AEC. By 1954 and the Castle Bravo incident, it was obvious that radioactive fallout was dangerous to humans. United States Atomic Energy Commission Division of Biology and Medicine dealt with efforts directed towards experimental and field studies and the correlation of data dealing with Project GABRIEL.
The RAND Corporation, Laboratories at Columbia University, AEC's New York office, the University of Chicago, an exclusive group of scientists, UCLA, and the United States Air Force were all involved in collection and testing of samples from around the world for radioactive fallout.