** The Centers for Disease Control are part of the U.S. Department of Health and Human Services (formerly the U.S. Department of Health, Education, and Welfare). In late 1977, DOD began a study to provide data to both the Centers for Disease Control and the Veterans Administration on potential exposures to ionizing radiation among the military and civilian participants in atmospheric nuclear weapons testing. DOD organized an effort to: o Identify DOD personnel who had taken part in the atmospheric nuclear weapons tests o Determine the extent of the participants' exposure to ionizing radiation o Provide public disclosure of information concerning participation by military personnel in Project TRINITY. METHODS AND SOURCES USED TO PREPARE THIS VOLUME This report on Project TRINITY is based on historical and technical documents associated with the detonation of the first nuclear device on 16 July 1945. The Department of Defense compiled information for this volume from documents that record the scientific activities during Project TRINITY. These records, most of which were developed by participants in TRINITY, are kept in several document repositories throughout the United States. In compiling information for this report, historians, health physicists, radiation specialists, and information analysts canvassed document repositories known to contain materials on atmospheric nuclear weapons tests conducted in the southwestern United States. These repositories included armed services libraries, Government agency archives and libraries, Federal repositories, and libraries of scientific and technical laboratories. Researchers examined classified and unclassified documents containing information on the participation of personnel from the MED, which supervised Project TRINITY, and from the Los Alamos Scientific Laboratory (LASL), which developed the TRINITY device. After this initial effort, researchers recorded relevant information concerning the activities of MED and LASL personnel and catalogued the data sources. Many of the documents pertaining specifically to MED and LASL participation were found in the Defense Nuclear Agency Technical Library and the LASL Records Center. Information on the fallout pattern, meteorological conditions, and nuclear cloud dimensions is taken from Volume 1 of the General Electric Company-TEMPO's "Compilation of Local Fallout Data from Test Detonations 1945-1962, Extracted from DASA 1251," unless more specific information is available elsewhere. ORGANIZATION OF THIS VOLUME