Which agency is responsible for organizing, training, and equipping aerospace forces?

The Headquarters, United States Air Force (HAF) is the correct answer because it serves as the central organizational and command authority for the USAF. HAF is responsible for developing and implementing policies, plans, and programs for organizing, training, and equipping aerospace forces to ensure they are prepared for operational readiness and effectiveness. It directs the overall strategy for the Air Force and oversees the various components that contribute to military aerospace operations.

This answer highlights the HAF's unique position within the military structure, emphasizing its role in not only command and control but also in strategic planning and resource allocation necessary for the capability and modernization of aerospace missions. The other agencies listed, while integral to the military framework, do not specifically focus on the overarching responsibility of organizing, training, and equipping air forces at the national level as the HAF does.