218. A guard patrol consists of one or more men detailed for the
performance of some special service connected with guard duty.
219. If the patrol be required to go beyond the chain of sentinels,
the officer or noncommissioned officer in charge will be furnished
with the countersign and the outposts and sentinels warned.
220. If challenged by a sentinel, the patrol is halted by its
commander, and the noncommissioned officer accompanying it advances
alone and gives the countersign.