In addition to the protection of a column on the march, Flank Guard work is of the highest importance on the Lines of Communications and in the protection of Convoys. On the _Lines of Communications_ raids from the air or land may always be expected in Manoeuvre Warfare, and one flank is usually more vulnerable than the other. A _Convoy_, when parked, is liable to attack from any quarter; and when on the march it may be assailed from any direction, especially when the adversary can detach mounted troops, or infantry rendered mobile by motor transport, or raiding bodies carried in Aircraft. Frequently, however, one flank only of the Lines of Communications is vulnerable owing to the geographical or tactical situation, and the work of protecting traffic or Convoys on the Lines of Communications is Flank Guard work, with due precautions against surprise from all quarters, the Main Guard remaining with the Convoy and securing its safe arrival at its destination, rather than seeking an encounter with the enemy. The most efficient way to protect a Convoy is to piquet the road daily with troops sent out from posts on the line; but when it is necessary to send a Convoy by a route which cannot be protected in this way a special escort must be provided. The commander of an escort will not engage the enemy if his task can be accomplished without fighting. If fighting is inevitable the enemy should be engaged as far from the Convoy as possible, and it will not be halted and parked, except as a last resort. In the case of mechanical transport the whole of the escort will be carried in motor vehicles, and except where parallel roads are in existence, little can be done to secure flank protection while on the move. A portion of such escort will move with the Convoy and a portion will be sent ahead to secure any bridges or defiles which have to be passed, the outlet of any defile being secured before the Convoy is permitted to enter the defile. In the case of a horsed Convoy the escort will usually consist of infantry, with a proportion {117} of mobile troops. Small Advanced and Rear Guards will be detailed and sufficient men will be posted along the column to ensure order and easy communication. The remainder of the escort will usually move on that flank from which attack is most likely.