The commanding officer directs the use of the countersign. Sentries of an interior guard may use the countersign, but countersigns are primarily for use by sentries or persons defending tactical areas.

By Whom Authorized

When a countersign is prescribed, the highest headquarters within a zone or area devises it. The authority to designate a countersign may be delegated to subordinate units for their immediate use when necessary; however, these units must notify higher headquarters of such action without delay. Only one countersign can be used within a command during a specified period.

Selecting the Countersign

The choice of words or sounds for the countersign is made with care. When possible, words are selected that are difficult for the enemy to pronounce. The word selected for the secret challenge, or countersign must not suggest the word selected for the password. Doing this minimizes the possibility of an unauthorized person guessing the password. (For example, the secret challenge, ATOMIC, suggests the password BOMB.)

Using the Countersign

The initiative for use of the countersign rests with the challenging sentry. Positive recognition of each person claiming authority to pass is the main consideration of the sentry. When he does not visually recognize the challenged person or party, he uses the countersign to make a positive recognition. When there is any doubt as to the authority of the challenged person to pass, even if he gives the correct password, he is detained for further action by the corporal of the guard. When the sentry recognizes the challenged person or party before using the countersign and there is no doubt the person or party has authority to pass, the sentry does not use the countersign.

Mutual identification is essential. If the person challenged does not recognize the secret countersign, he should not give the password.

When a secret challenge and password are prescribed, the secret challenge is given by the sentry after the person is advanced to be recognized. The person challenged should then give the password. Both the secret challenge and the password are given in a low tone to prevent them from being heard by others.

For example, a sentry observes a person approaching his post during the time for challenging. When the person is still far enough away from the sentry's post for the sentry to take effective measures should the person rush him after being challenged, he commands, "HALT! WHO IS THERE?" After receiving an answer (such as, "Lieutenant Jones, Company B") indicating the person is friendly and may be authorized to pass, the sentry says, "Advance, Lieutenant Jones to be recognized." When Lieutenant Jones reaches a point where the secret challenge, spoken in a low tone, can be heard only by him, the sentry again commands, "HALT!" then he gives the secret challenge or countersign, in a low tone (for example, "SNOWFLAKE"). After receiving the correct password from Lieutenant Jones (for example, "ROOSTER") and otherwise satisfying himself that the Lieutenant is authorized to pass, the sentry says, "Advance, Lieutenant Jones" and salutes, if appropriate. If Lieutenant Jones is one of a party challenged and is the person advanced according to the procedures discussed here, the sentry then tells Lieutenant Jones to bring up his men and identify each individual before he passes.