Which entity serves as the Secretary of Defense (SecDef) in the context of the National Industrial Security Program?

The Department of Defense (DoD) serves as the Secretary of Defense (SecDef) in the context of the National Industrial Security Program (NISP) because the SecDef is the principal defense policy advisor to the President and oversees the military and the defense-related activities of the government. The NISP's purpose is to ensure that contractors and other entities that handle classified information are properly safeguarding it in line with national security requirements, and the DoD is the primary federal agency responsible for managing this program.

The SecDef's role encompasses ensuring that industrial partners adhere to security standards and practices that protect classified information critical to national defense, thus directly linking their authority and responsibilities to the objectives of the NISP. The other departments listed—Homeland Security, Energy, and State—while they play roles in various aspects of national security and policy, do not hold the authority of the SecDef nor are they directly responsible for the NISP in the same capacity as the Department of Defense.