What kind of order does the Secretary of Defense issue to prepare forces for deployment?

The correct choice is the Deployment Order, which is issued by the Secretary of Defense to prepare forces for deployment. This order typically outlines the specific requirements necessary to ready military units for an upcoming operation or mission. It provides essential guidance, including timelines, locations, and resources needed for the deployment, ensuring that all personnel and equipment are appropriately prepared.

The term "deployment" directly refers to the act of moving forces into position for military action, making this order essential for operational readiness. It encompasses all the logistical and strategic elements needed to ensure that troops can be moved efficiently and effectively.

The other terms may lack the specific context that the Deployment Order encompasses. For instance, an Activation Order commonly refers to formally bringing reserve forces into active duty but doesn't specifically denote preparation for deployment in the same comprehensive way. Similarly, a Preparation Order may suggest readiness actions, but does not capture the full scope of what is included in a Deployment Order. A Mission Order generally pertains to the specific objectives of a particular mission rather than the overarching preparations for deployment, which is crucial in military operations.