the adversary's intelligence collection capabilities identified in the previous action. Threat can be thought of as the strength of the adversaries, while vulnerability can be thought of as the weakness of friendly organizations. Assessment of Risk: First, planners analyze the vulnerabilities identified in the previous action and identify possible OPSEC measures for each vulnerability. Second, specific OPSEC measures are selected for execution based upon a risk assessment done by the commander and staff. Risk is calculated based on the probability of Critical Information release and the impact if such as release occurs. Probability is further subdivided into the level of threat and the level of vulnerability. The core premise of the subdivision is that the probability of compromise is greatest when the threat is very capable and dedicated, while friendly organizations are simultaneously exposed. Application of Appropriate OPSEC Measures: The command implements the OPSEC measures selected in the assessment of risk action or, in the case of planned future operations and activities, includes the measures in specific OPSEC plans. Countermeasures must be continually monitored to ensure that they continue to protect current information against relevant threats. The U.S. Army Regulation 530-1 refers to "Measures" as the overarching term, with categories of "Action Control" (controlling one's own actions); "Countermeasures" (countering adversary intelligence collection); and "Counteranalysis" (creating difficulty for adversary analysts seeking to predict friendly intent) as tools to help an OPSEC professional protect critical information. An OPSEC Assessment is the formal application of the process to an existing operation or activity by a multidisciplinary team of experts. The assessments identify the requirements for additional OPSEC measures and required changes to existing ones. Additionally, OPSEC planners, working closely with Public Affairs personnel, must develop the Essential Elements of Friendly Information (EEFI) used to preclude inadvertent public disclosure of critical or sensitive information. The term "EEFI" is being phased out in favor of "Critical Information", so all affected agencies use the same term, minimizing confusion. History Vietnam In 1966, United States Admiral Ulysses Sharp established a multidisciplinary security team to investigate the failure of certain combat operations during the Vietnam War. This operation was dubbed Operation Purple Dragon, and included personnel from the National Security Agency and the Department of Defense. When the operation concluded, the Purple Dragon team codified their recommendations. They called the process "Operations Security" in order to distinguish the process from existing processes and ensure continued inter-agency support. NSDD