Which of the following best describes operational security (OPSEC)?

Operational security (OPSEC) is fundamentally concerned with the protection of sensitive information from adversaries. It involves identifying critical information, analyzing threats, assessing vulnerabilities, and applying measures to maintain the confidentiality of that information. By implementing OPSEC, military organizations can prevent unauthorized access and reduce the risk of valuable operational details being exposed, which could jeopardize missions or the safety of personnel.

The other options focus on different aspects of military and organizational effectiveness. Evaluating personnel fitness pertains to assessing individuals' capabilities and health rather than protecting information. Managing resources is about optimizing the use of assets, which does not specifically address security concerns. Conducting drills is important for readiness and training but does not directly involve safeguarding information. Hence, the choice that accurately captures the essence of operational security is the one that emphasizes the protection of sensitive information.