Which department is responsible for overseeing national defense in the U.S.?

The Department of Defense is the primary agency responsible for overseeing national defense in the United States. It manages the nation's military and coordinates all branches of the armed forces, including the Army, Navy, Air Force, Marine Corps, and Space Force. The department's mission encompasses protecting national security, conducting military operations, and ensuring readiness against threats. It is structured to address various security challenges and plays a crucial role in formulating national defense policies.

In contrast, the Department of Justice focuses on enforcing federal laws, representing the government in legal matters, and ensuring fair and impartial administration of justice. The Department of Homeland Security primarily deals with domestic security issues, such as immigration and terrorism prevention, rather than military defense. The Central Intelligence Agency is responsible for collecting and analyzing information related to national security from around the world, but it does not oversee national defense operations directly. Thus, the Department of Defense stands out as the correct answer as it is dedicated specifically to managing and executing defense strategies for the country.