ABSTRACT Operation Castle consisted of six nuclear detonations at the Eniewtok Proving Ground during the period 1 March to 14 May 1954. Two were surface or near-surface land shots: one on a natural island and the other on a man-made island at the end of a causeway. The other four shota were fired on barges: two anchored in reef craters from previous shots and the other two anchored in the lagoon proper. The Department of Defense (DOD) military-effect program consisted of 37 projects divided among six planned programs and one program (biomedical) added in the field; in addition, one Los Alamos Scientific Laboratory (LASL) program (thermal radiation) was concerned with an area of military-effect interest. Program 1, the blast program, was designed to document information on shock parameters in the propagation of the blast wave incident on and through the media of air, ground, and water for devices with yields in the megaton range. Program 2, the nuclear-radiation program, had two primary objectives: documentation of the initial neutron and gammaradiation, and documentation of fallout from landsurface and water-surface bursts; both efforts were devoted to miltimegaton-yield devices. Program 3, the blast-effect program, concentrated on (1) obtaining loading data for predicting structural response and damage from multimegaton air blast, (2) gathering data on the dimensions of apparent craters formed by multimegaton-yield shots for use in crater~size prediction, (3) studying blast damage to forested areas, and (4) determining the effects on a planted sea minefield from a water-surface detonation. Program 4, the biomedical program, was organized immediately after the accidental exposure of human beings on Rongelap, Ailinginae, Rongerik, and Uterik to the fallout frorn Shot 1, in order to (1) evaluate the severity of the radiation injury to those exposed, (2) provide all necessary medical care, and (3) conduct a scientific study of radiation injuries to human beings. Program 6 was a composite program covering tests of service equipment and techniques. The ultimate objective of the aircraft-participation projects was the establishment of operational and design criteria concerning nuclear-weapon delivery aircraft, both current and future; measurements of overpressures, gust loading, and thermal effects were made on aircraft in flight. In order to evaluate washdown countermeasures, two converted, remote-controlled Liberty ships were placed in multimegaton fallout patterns. In addition to simulating tactical conditions aboard a ship during and after fallout, these vessels were equipped to collect fallout on their weather surfaces for contamination-decontamination studies and housed instrumentation for studies of fallout material. Aliso, their weather surfaces served as a radiating surface for shielding studies. Lastly, one project studied effects on the ionosphere. Program 7, the long-range-detection program, was concerned with the problem of detecting and locating the detonations and documenting them to the maximum extent possible. Program 9 performed the photographic documentation function. In addition, a photo- 5