personnel were present at these tests, lists the DOD organizations represented, and describes their activities. It discusses the potential radia- tion exposure involved in these activities and the measures taken for the protection of personnel from these participating DOD organizations. presents the exposures recorded by the participating DOD units. It The in- formation is limited to these points. Historical Background CASTLE was the culmination in the development of the super, or hydrogen, bomb that began in 1950. Fusion, or thermonuclear, reactions had been used in 1952 to generate a very powerful detonation of the MIKE device in Operation IVY, but MIKE was not a deliverable nuclear weapon. In BRAVO, the first test of the CASTLE series, a device more powerful than MIKE was exploded that, although not a weapon, was capable of delivery by an aircraft (Reference 1). The BRAVO detonation also generated a cloud of device debris and coral particles that brought unexpected heavy exposures of ionizing radiation to some of the U.S. servicemen aiding in the conduct of the tests, to foreign fishermen, and to Marshall Islands residents. Radiation injuries resulted to some in the latter groups. CASTLE also was the first Pacific test in which the University of California Radiation Laboratory (UCRL) at Livermore provided a nuclear device for testing, detonatedas the KOON event of the series. All previous nu- clear test devices had been designed at the Los Alamos Scientific Labora-~ tory (LASL), New Mexico. Report Organization Subsequent sections of this overview chapter discuss the form of experimental nuclear weapon test programs with the emphasis on the potential radiation exposure of participating DOD personnel. The experimental ac- tivities are considered first without particular reference to the geographic location of the testing, and are then related to the geographic 26