What department is the Secretary of Defense associated with?

The Secretary of Defense is associated with the United States Department of Defense, which is responsible for coordinating and supervising all agencies and functions of the government relating directly to national security and the military. This department encompasses a wide range of responsibilities, including overseeing military forces, conducting military operations, and formulating defense policies. Given that the role of the Secretary of Defense is primarily focused on defense matters and military affairs, this connection is crucial for the effective management of the armed forces and strategic defense initiatives.