Having discussed in broad terms the security of troops in camp, we are prepared to consider their security while either advancing upon or retreating from the enemy. In either case groups are placed between our main body and the actual or supposed position of the hostile troops. When we are advancing upon an enemy our advanced groups constitute what we term the "advance guard." If we are retreating from the enemy, our rear groups compose the "rear guard." The main general ideas of an advance guard are illustrated by the husband who takes his wife and family to his house after an evening's absence. The house is dark and without occupants. The wife and children are apprehensive of danger. The husband goes first, turns on the light, and searches for any indications of an enemy. He looks, if desirable, in the closets and under the beds. If there is any one that may harm his family it is his duty to find out and dispose of him. In the advance guard we have exactly the same general scheme as with outposts. Far advanced to the front (and often to the sides or flanks) we have small groups (called, when considered collectively, the "advance party") whose business it is to inform us of the presence of the enemy. Next we have a large group ("support") to assist these small and rather helpless ones in advance in case of difficulty. And last we have a still larger group ("reserve") that may be called upon in great emergencies. We should fully understand that all these groups are out to accomplish several ends, but their one great and ultimate object should be to push on ahead of the main body so that it may be secure and its march uninterrupted. To accomplish this it is desirable to get all possible information about the enemy; it is also desirable to keep him from getting any information about your own troops. The ideas are nearly the same with rear guards. Note this important difference: if, in an advance upon the enemy, your advance guard should suddenly be fired upon, your main body would (temporarily) halt. If, in a retreat, your rear guard is halted by the enemy's fire, your main body would normally be marching farther from it. In the first case assistance is near at hand. In the second it is withdrawing. The rear guard in a retreat should therefore be a little larger than in an advance. It must be able to extricate itself from any situation however difficult or it loses its usefulness. Its commander should have a cool, level head. To delay the enemy and thus assist the main body to escape is his mission. For him to remain too long in a good position might endanger not only his safety but that of the main body as well. CHAPTER VIII ATTACK AND DEFENSE