Which order serves as a formal statement to alert units of impending operations?

The correct choice is a Warning Order, which serves as a formal notification to military units about impending operations. This order provides initial guidance and critical information to prepare personnel and resources. It is typically issued before a Deployment Order or Mission Order and includes details about the nature of the operation expected to occur, although it does not contain final directives. The Warning Order helps units begin planning and mobilizing while allowing time to gather necessary intelligence and make logistical arrangements.

In a military context, this type of order is essential for ensuring that all units involved are adequately prepared for what's to come, making it a vital element of operational readiness. The proactive nature of a Warning Order allows units to understand the expected timeline and develop preliminary actions, which is key for coordination and timely execution of plans.