Fallout sampling and other nuclear intelligence techniques were the most important sources of United States strategic intelligence in the early Cold War. Operated as the Atomic Energy Detection System by a covert Air Force unit known as AFOAT-1, the AEDS detected emissions and analyzed fallout from Soviet nuclear tests, as well as provided quantitative intelligence on the size of the Russian nuclear stockpile. Virtually unknown because the only greater Cold War secret than nuclear weapons was intelligence gathered about them, data on the Soviet threat produced by AFOAT-1 was an extraordinary influence on early National Intelligence Estimates, the rapid growth of the Strategic Air Command, and strategic war plans. Official guidance beginning with the first nuclear test in 1945 otherwise suggested fallout was an insignificant effect of nuclear weapons. Following AFOAT-1's detection of Soviet testing in fall 1949 and against the cautions raised about the problematic nature of higher yield weapons by the General Advisory Committee, the Atomic Energy Commission’s top scientific advisers, President Harry Truman ordered the AEC to quickly build these extraordinarily powerful weapons, testing the first in secrecy in November 1952. In spring 1954, the second test of an American thermonuclear (or hydrogen) bomb, CASTLE BRAVO, produced more than 7,000 square miles of potentially lethal fallout deposition near its ground zero, as well as contaminating people and fish in a notorious fallout radiation exposure incident. These tests also produced residual fallout that intensified every spring as it returned from the stratosphere. In April 1954, J. Robert Oppenheimer, formerly scientific director of the Manhattan Project and chair of the AEC's GAC, was permanently stripped of his clearance to handle classified information, ostensibly for failing to display sufficient enthusiasm during development of this weapon. This hearing was effectively a sham that served as a proxy for Air Force efforts to silence his concerns and those of a secret AEC study named GABRIEL, warnings that in the event of war the problematic nature of the cumulative fallout from these weapons would afflict the populations of both the victim and the aggressor as they contaminated the global environment. The transnational public outcry in the years that followed the CASTLE BRAVO fallout incident put intense pressure on political leaders to end testing. The deciding factor at the White House proved to be several instances of fallout contamination of the food supply involving wheat and milk. Tellingly, this was due to the limited fallout from testing alone. This data provided an empirical basis to underwrite earlier cautions that general nuclear war would yield no winner, only varying degrees of loss. Utilizing the high-altitude capabilities of the U-2, the data that proved the need for caution was provided to researchers by the Air Force. No longer as useful a secret, the military, too, came to see fallout as an issue that unnecessarily problematized their reliance on nuclear weapons. To blunt efforts to achieve a comprehensive test ban, the Air Force pursued underground testing to forestall continuing fallout that would raise deeper questions about the viability of nuclear war itself. Rather than a mere propaganda problem, as it was often seen by officials, fallout proved to be a practical limitation on the use of nuclear weapons. The 1963 Limited Test Ban Treaty that resulted ended most atmospheric testing, but not the possibility that fallout could some day contaminate the planet
