Which term refers to the measure taken when ground attack by forces is imminent or in progress?

The term that specifically refers to the measure taken when a ground attack by forces is imminent or in progress is best understood in the context of military alerts. The phrase "Bugle Playing 'Call to Arms'" resonates with historical military practices, where such calls are made to rally troops and prepare them for imminent combat or attack scenarios.

This call is an immediate and recognizable signal used to indicate that forces should prepare for engagement or defend against an attack, thereby ensuring that personnel are alerted promptly to the potential threats they face. In a military setting, such alerts are crucial for maintaining readiness and coordinating responses to actual combat situations.

Other options may pertain to alert systems but do not specifically denote the immediate action required during an active ground attack. Therefore, the specific term that encapsulates the urgency and context of a ground attack is indeed represented by the traditional military function of a bugle signal.