Now you are to handle groups on the defense. You must bear in mind that there are two kinds of defense: first, where you do nothing but defend (passive defense); second, where you defend, but temporarily, with the idea of attacking the enemy as soon as a favorable opportunity arises (active defense). Let us assume that you have been ordered by superior authority to locate and prepare a definite position to check the advance of an enemy. Just what main points should you bear in mind? Suppose you have found an ideal position; what conditions should it fulfil? You should be able to see the enemy long before he arrives at your position. Intervening objects and trees would make that impossible. You should be hidden from his view. The ends of your lines (your flanks) should rest, if possible, on ground easy to defend; for instance, a high mountain, a large body of water, or an impassable swamp. A few acres of ground will not hold tens of thousands of men. Therefore the extent of the ground must be suitable for the size of your group (force or command). It would be of great advantage to have such cover that one group (for instance, a support) could move from this position to that without danger of being fired upon or observed. A wise general has plans for any contingency. He is either going to win or he is not going to win. If he loses, he should have a means of escape (retreat). In selecting his position he should place it where the enemy must attack or give up his mission. Verdun had to be attacked before the advance on Paris from the east was practicable. In defense there is a generous allowance of advantages. Usually you have time to select and prepare your position. By preparing a position we mean, you can dig trenches, destroy intervening objects that obstruct the view of what you should see, construct obstacles that will embarrass the enemy in his advance, estimate (or determine) distances to important places. You have opportunities for collecting ammunition, arranging wires for communication, establishing stations for the wounded. Troops in motion are easier to see. You are not called upon for as much physical strain as the attacking troops. You are less fatigued. Your machine guns are better concealed and the gunners know the ranges better than those of the attack. But it is most distressing to a man on the defense to see the enemy, regardless of everything he can do, advance step by step. He begins to question within himself the efficacy of his fire, which is to doubt his own ability. The more he questions and worries, the less effective his aim becomes. His comrades are dead and wounded about him. Their cries of distress are heard above the noise and confusion of battle. He becomes less methodical and deliberate in his actions. His shooting becomes high and wild. This becomes generally true. The attacking force gains fire superiority.