What does the Secretary of Defense (SecDef) approve to announce the selected course of action?

The correct answer is Alert Order (ALERTORD). An Alert Order is issued by the Secretary of Defense to inform appropriate military and civilian authorities of the selected course of action. It serves as a directive to prepare for potential military operations, ensuring that all necessary entities are ready to react swiftly to the situation at hand.

In this context, the Alert Order is designed to alert the relevant personnel and resources about the decision so they can commence pre-positioning and coordination efforts aligned with the approved plan. This readiness is critical for effective response and implementation as operational circumstances develop.

The other options, while related to military operations, serve different purposes. An Execution Order (EXORD) provides the specific authority to commence operations but follows the initial alert process. An Operational Plan (OPLAN) outlines broader strategies and tactical operations but does not itself serve as an announcement of a selected course of action. A Mission Assignment (MA) pertains to assigning tasks and resources for specific operations, which comes after the course of action is selected and announced.