In the Navy, what is the term for a ship leaving port for a mission?

The term "underway" in the Navy signifies that a ship is not anchored or moored and is actively moving through the water. This term is crucial as it indicates the ship is in a state of operation, ready to carry out its mission at sea. When a naval vessel is underway, it may be engaging in various activities, including training exercises, patrols, or heading towards a specific deployment location.

While "departing" generally refers to leaving a particular location, it does not encompass the broader context of a ship’s operational status at sea. "Deploying" is used in some contexts to describe the act of sending forces into action, typically for a mission, but does not specifically refer to the ship’s mobility or status while at sea. "Setting sail" is more commonly associated with sailing vessels and doesn't reflect the unique terminology used in naval operations. Therefore, "underway" is the precise term that encapsulates a ship’s readiness and activity level when it has left port for a mission.