What is a running password used for?

A running password is a tactical tool employed to confirm the identity of individuals or units approaching a particular location, typically in a combat or high-alert situation. The primary purpose of a running password is to enhance security by ensuring that only friendly forces are able to approach without raising an alarm or entering into a hostile engagement. It is used during operations where the potential for encountering enemy forces is significant, making it critical for units to maintain effective communication and recognition protocols.

Option B accurately reflects this function as it highlights the importance of using a running password to alert the unit that friendlies are approaching. This mechanism reduces the risk of friendly fire incidents and helps to maintain operational security. In contrast, other options suggest uses that do not align with the established tactical guidance for running passwords, such as communicating with enemy forces or signaling the end of a mission, which are not appropriate uses of this security measure.