THE PURPOSE OF THE STUDY IS TO HELP DESIGNERS OF SECURITY SYSTEMS DEVELOP CRITERIA FOR PROTECTING NUCLEAR FACILITIES AGAINST ASSAULT, FOR GUARDING NUCLEAR MATERIALS AGAINST THEFT AND DIVERSION, AND FOR DEALING EFFECTIVELY WITH SUCH EPISODES SHOULD THEY OCCUR. COMPOSITE PROFILES OF POTENTIAL NUCLEAR ADVERSARIES WERE DEVELOPED BY ANALYZING SEVERAL HUNDRED INCIDENTS ANALOGOUS TO ATTACKS ON NUCLEAR PROGRAMS SUCH AS MAJOR ARMED ROBBERIES AND BURGLARIES, TERRORIST ASSAULTS, SMALL-SCALE MILITARY AND PARAMILITARY RAIDS, INDUSTRIAL SABOTAGE, AND SYMBOLIC BOMBINGS. THREATS AGAINST AND ACTUAL INCIDENTS AT NUCLEAR FACILITIES WERE ALSO EXAMINED. THE COMPOSITES SUGGEST THAT POTENTIAL ADVERSARIES OF NUCLEAR PROGRAMS WOULD HAVE NO PROBLEM OBTAINING RESOURCES. THEIR WEAKNESS IS TO BE FOUND IN LESS TANGIBLE, HUMAN FACTORS INCLUDING IMAGINATION AND INGENUITY, CRIMINAL SKILLS, TECHNICAL KNOWLEDGE, WILLINGNESS TO RISK CAPTURE OR DEATH, ACCURATE INTELLIGENCE AND PRIVILEDGED ACCESS, AND ABILITY TO ACHIEVE TACTICAL SURPRISE. SECURITY DESIGNERS SHOULD EXPLOIT THESE SOURCES OF WEAKNESS, FOCUSING ON MONITORING PHYSICAL BARRIERS, PUBLICIZING THE RISKS INVOLVED IN ATTACKING A NUCLEAR FACILITY, DELIBERATELY CREATING UNCERTAINTY ABOUT THE STRENGTH AND ROUTINE OF GUARD FORCES, AND DEFEATING ATTACKS BEFORE TERRORISTS GAIN ENTRY TO A FACILITY, RATHER THAN CONTAINING AN ASSAULT AFTER IT IS DISCOVERED. DETAILS OF THE ANALYSIS, FINDINGS, AND SECURITY IMPLICATIONS ARE PROVIDED, TOGETHER WITH A SUMMARY, A GLOSSARY, AND AN OUTLINE OF NUCLEAR THREAT CHARACTERISTICS (LIKELY ADVERSARIES, MOTIVES, ADVERSARY ATTRIBUTES, TACTICAL OBJECTIVES, MODES OF ACTION, CONSEQUENCES, CHARACTERISTICS OF THE OPERATION) CONSIDERED IN THE ANALYSIS. (LKM)