The march in the narrow boyau of an unknown sector, in the darkness, and with full equipment, is difficult and depressing. Consequently, the rate of march must be slow. When the head of the column meets an obstacle, a warning word is passed to the rear along the single file. This rule is above all useful to prevent accident to telephone wires. The march must be executed without noise. Orders are given in low tones. Smoking or the use of flashlights is prohibited. No disciplinary measure is too severe that will prevent the enemy from discovering the relief. It is absolutely prohibited to talk over the telephone concerning a relief otherwise than in cipher. IV. Occupation of the Position =Details of the Relief.= If the two units have the same number of men, the relieving of one unit by the other is simple enough. But often the relief is complicated by the fact that either the extent of front or the number of effectives is different. In such a case, the officers of the two units must settle, during the reconnaissance, upon the necessary modifications for an effective and expeditious relief. When the company arrives at the command post of the captain, the platoons are relieved from right to left in the first line, then in the cover trench in the same order. If there is a platoon in the support line this is next relieved. In the first line, the relief of the platoons is executed in two parts. First of all, the sentinels, observers, watchers, men in the listening posts, and the N. C. O. of the watch are relieved. When this is done, the remaining men of the platoon are relieved. The men of the old platoon occupy their places at “Stand To.” The relieving platoon files in and steps up on the firing step. At the command “Pass” which is given quietly, the old and new platoons change places. Each retiring leader, of whatever command he may be, hands over his orders and information to the corresponding leader who relieves him. For example, one platoon leader will turn over to the other all information concerning guard duty, defense of the line, condition of the barbed wire entanglements, patrolling, and shelter accommodations. This must be executed rapidly but with precision. The platoon relieved assembles at the entrance to the boyau, and leaves the trenches under the chief of platoon. This is not done, however, until the platoon leader has reported to his captain, by means of his guides, the execution of the relief. The old captain fixes a point for the assembling of his platoons, but this point must be far enough to the rear to avoid blocking of the boyaux and out of reach of hostile grenade and trench mortar fire.