INTRODUCTION It is the primary purpose of this report to interpret and make record of test operation data and experience which will be of greatest use to those responsi- ble for the continued maintenance and development of the proving ground. More specifically, the report has been compiled with a view toward its reference value to the Atomic Energy Commission. Although this report is supplemental in nature to the more comprehensive reports prepared by the Commander, Joint Task Force SEVEN for the Joint Chiefs of Staff, it is intendedto be complete to the extent required in the satisfactory attainment of its aims. The entire report is comprised of three principal parts. Part I presents a general over-all concept of the Operation from the AEC Santa Fe Operations point of view and includes recommendations for future operations; PartII is the scientific version of the Operation's aims and accomplishments as pre* sented by the Los Alamos Scientific Laboratory (LASL) and the University of California Radiation Laboratory (UCRL); Part III presents the managerial or administrative aspects of the Operation. For a more comprehensiveaccount of the LASL participation in the Operation, reference is made tothe Report of the Commander, Task Group 7.1 for Operation CASTLE. Detailed coverage of the Contractor's activities may be found in the Completion Report for Operation CASTLE as prepared by Holmes & Narver, Inc. PART CHAPTER 1. I GENERAL ACCOUNT SUMMARY 1.1.) OPERATION SITE The Atomic. Energy,Commission's Pacifié Proving Ground (PPG) ,;com- prises Eniwetok and Bikini Atolls in the Marshall Islands. Prior to the first CASTLE shot the water area surrounding these atolls and bounded by Lat: 12° 45'N on the North, Long. 166° 16' E on the East, Lat. 10° 15' N on the South, and Long. 160° 35' E on the West was establishedas a danger area, and unauthorized entrance by wateror air was prohibited. The far-reaching fall-out effects occasioned by the first CASTLE shot prompted an immediate enlargement of the danger area for the balance of the Operation. The modified danger area is described as a circular segment centered at Lat. 12° N, Long, 164° E, with a radius of 450 nautical miles, and arc lengths extending fromtrue bearings 240° to 95° in a clockwise direction. Figure 1] shows the proving ground and danger areas. 1.2 OPERATION SCOPE AND SCHEDULE Operation CASTLE was a full-scale test operation developed by the Atomic Energy Commission (AEC) for testing nuclear devices and experimental