Which General Order requires a sentry to be on alert constantly?

General Order 2 is vital for maintaining security and vigilance as it specifically states that a sentry must remain constantly on alert. This requirement emphasizes the importance of situational awareness in ensuring that no unauthorized personnel or threats go unnoticed. Constant alertness is essential for the safety of the facility or area the sentry is tasked to protect.

The other choices, while also important, focus on different responsibilities. For example, the first general order emphasizes the duty of the sentry to take charge of their post, while the third and fourth orders outline procedures for reporting violations and receiving orders. However, these do not specifically address the expectation of continuous alertness that is articulated in General Order 2.