Service-specific functions were initially outlined by President Truman in which Executive Order?

The correct answer regarding which Executive Order outlined service-specific functions by President Truman is Executive Order 9877. This order was significant because it established the framework for the Department of Defense and clearly delineated the roles of the different military branches. By defining the organizational structure and component relationships within the military, the order facilitated more effective coordination and function among the services.

In the broader context, Executive Order 9082 focused on the creation of the Department of Defense as a unified command structure, but it did not specifically address the individual service functions. Executive Order 12759 and Executive Order 13467, while relevant to military and intelligence operations, were issued much later and pertained to different issues within the defense establishment, thus not contributing to the initial outline of service-specific functions as Executive Order 9877 did.