Which agency is primarily responsible for security investigations in the Navy?

The correct answer is NCIS, which stands for the Naval Criminal Investigative Service. This agency functions as the primary investigative agency for the Navy, focusing on a variety of matters, including security investigations. NCIS is dedicated to protecting the Navy and Marine Corps by conducting criminal investigations, counterintelligence, and anti-terrorism initiatives. Its specialized role and expertise in military matters make it the most appropriate agency for conducting security investigations within the Navy.

The FBI, while a key federal law enforcement agency, does not specifically focus on the internal security matters of the Navy. The Coast Guard has a broader mission related to maritime safety and security but does not primarily handle Navy security investigations. The Defense Counterintelligence and Security Agency is involved in broader national security and counterintelligence efforts but operates on a larger scale beyond just the Navy, making NCIS the most relevant agency for this context.