Who is responsible for posting the relief for sentries?

The correct answer is the Corporal of the Guard. This individual is directly responsible for the supervision of sentries and the overall functioning of the guard detail. The Corporal of the Guard ensures that sentries are relieved in a timely manner to maintain effective security operations. This role is vital as it ensures that sentries are alert and able to perform their duties without becoming fatigued, thereby maintaining the integrity of the guard’s responsibilities.

While the Sergeant of the Guard and Officer of the Day utilize the Corporal of the Guard to execute their orders, the direct action of posting relief, which involves physically replacing sentries and ensuring they are properly briefed, falls under the Corporal's duties. The Commanding Officer oversees the entire operation but does not typically involve themselves in the daily management of sentry relief.