PREFACE The preparation of any report is necessarily the direct work of only a few people; yet the very existence of this final product is the summation of the material contributions of a large number of persons who remain anonymous. The authors thank the many members of the Army Signal Engineering Laboratory (ASEL) ~ who were responsible for the development and construction of the gamma-intensity-time recorders loaned to the project for Operation Hardtack. Special thanks are due Mr. Basil Markow and Mr. Richard G. Rast of ASEL who joined the project as consultants in the field and as specialists in ASEL instrumentation. . Special thanks are also due Mr. Samuel C. Rainey of the Bureau of Ships (Code 372) who assisted with much of the theoretical work and with final data reduction in the field. Lastly, special thanks are due to Mr. Lansing E. Egeberg and Mr. Glynn A. Pence of the Naval Radiological Defense Laborato.y, both for their ceaseless and invaluable efforts as deputy project officers for operations in the field and for their continued work on many and varied problems of data reduction during the preparation of the final report. In a project of the size and complexity of the one reported on, the number of contributions is so large as to require brevity, yet the gratitude of the authors for both material assistance and moral support is nonetheleas genuine. The following list is by no meana complete but rep- resents a Summary of principal contributors: For deep-anchoring theory and coracle design; James L. Faughn and Lyle D. Johnson. For radiation field theory; Rodney Buntzen, Arthur B. Denison, and Edwin S. Shapiro. For design of specialized electronic instrumentation; Benjamin Chow, Philip A. Covey, Richard R. Soule, and Harry A. Zagorites. For design af specialized mechanical instruments; Robert A. Nelson and John I. Pond. For design and implementation of special site chemistry; Roger Caputi, William R. Schell, and Edward R. Tompkins. For devising specialized readout techniques and reduction of taped data; Walter J. Gurney. For data reduction and preparation of the final report; Esther N. Guffy, Ichiro Hayashi, Morris Pasternak, Jean V. Sanderson, and Ann Swanson. For general assistance in many and varied problems; Roger Caputit, Louis B. Gomez, Gordon L. Jacks, Walter W. Perkins, Jack A. LaSpada, Dale H. Williams, and many others. v