A. THE TWO MAIN CLASSES OF RELIEF: 1. General Relief. Applied to the relief of a whole position manned by a division or more. Executed when large units are going to "full rest" in the rear or being removed from one part of the front to another. Executed in the same way as interior relief; i.e., by successive relief of the battalions involved. 2. Interior Relief. Applied to the relief of one sector or portion of a sector manned by a brigade or less. B. GENERAL PRINCIPLES OF RELIEF: 1. Interior relief is executed about once every six days; more frequently when the stay in the trenches is particularly arduous, less frequently when it is unusually comfortable. 2. The battalion is the relieving unit. 3. It is advisable to arrange the relief between units which have friendly relations to one another; e.g., battalions of the same regiment; and, so far as possible, to assign each unit to the same trenches on each relief. This promotes continuity of effort. 4. Relief is executed at night; the hour must be varied; secrecy is imperative. 5. Prompt execution is essential, to prevent fatigue of the troops and congestion of the boyaux. C. THE MECHANISM OF RELIEF: 1. Reconnaissance, 24 hours in advance, by the captain of each relieving company, accompanied by his platoon leaders and non-commissioned officers. He ascertains: (1) The plan of occupation; i.e., the dispositions and duties of the unit to be relieved. (2) The shelter accommodations. (3) Work being done and proposed. (4) Condition of the wire and other defences. (5) The available water supply. (6) Artillery support. (7) Communications. (8) The location, amount and condition of stores. (9) Danger points. (10) All available information of the enemy; his habits, location of his snipers, what work he is doing. (11) The ways and means of liaison, both lateral and from front to rear. To the success of this reconnaissance, the closest co-operation between all officers of the companies relieving and relieved, is indispensable.