Another important term which you continually meet with is the word communications. Every army moves forward from what is called its base—that is, the place where its ammunition, food, and general supplies are stored. These stores must be continually brought up to the army as it needs them; otherwise it would starve. There must, then, be a speedy and safe road or system of roads and railways between the army and its base. As the army advances this line of communications becomes longer and longer. It must be kept safe from the attacks of the enemy: for if a part of it between the base and the army were to be captured, the army would be cut off from its food and stores; and if it could not find a new line of communication, it would very soon be forced to surrender. Large numbers of soldiers are required to guard these lines of communications. You may think of them as the air-tube which supplies a diver with air. If by any means the air-tube should be cut or stopped up, the diver must immediately come to the surface, or perish.
Along the lines of communication there is a constant coming and going. Food, ammunition, general supplies, and new bodies of men are continually passing from the base to the front, and the wounded and the empty trains are continually being moved from the front to the base. When an army so spreads out that it has a wide front, it must have several parallel lines of communication, so as to keep itself supplied with the necessities of war.
So vastly important are these lines of communication that the opposing generals strive to cut them, and by so doing deprive their enemy of his supplies of food and ammunition.
Another important way in which a general seeks to overcome his enemy is by breaking through the line opposed to him in one or more places. If he succeeds in doing this, he has no longer a strong, united force opposed to him, but two or more fragments which he can overcome separately with his own united and unbroken force.
There are two ways of breaking an enemy's line. The first way is by holding the enemy all along his line, and suddenly bringing against one part of it a large, powerful force. If this force breaks through, it divides the opposing army, and can beat it in detail. Such an attack is known as a frontal attack. Napoleon tried it at Waterloo, but could not break through the "thin red line" of Wellington's heroes.
The other way of breaking the enemy's line is to outflank it, and then envelop or surround his forces. I have already used the word flank several times in these pages. It simply means the side or wing. If a man attacks you when you are sideways, you cannot well resist him. In order to do so you must turn your face towards him. So it is with an army. If it is attacked on its side or wing, it cannot properly resist until it forms a line facing the attacker. While it is doing this it runs the risk of being thrown into confusion, and perhaps destroyed.
Look at the diagram on p. [216]. Let A-F be a British force, and a-f a German force equal in strength. While these forces are fighting front to front, suppose a new British force, G H I, should appear, and attack the flank a. It is clear that the soldiers at a can only defend themselves if they swing round to meet the attack of G H I. If they remain where they are, they will very soon have the foe behind them as well as in front of them, and they will then be between two fires, in which case they can hardly escape destruction.
Suppose they swing round the two bodies a, b, as in Figure 1 (p. [217]) to meet G H I, what happens? The German line is weakened. Instead of having six bodies to meet six bodies, they have now only four to oppose the six of the attacking force. Immediately E F will try to take f in flank, and soon the line will assume the position shown in Figure 2 (p. [217]). You can easily see that the line of the enemy's communications is now in danger, and that if the movement continues the whole force will be surrounded. You will remember that the Germans managed to surround a large French army at Sedan and force it to surrender.[183] When a general finds himself being outflanked by a superior force, he is bound to retreat and straighten out his line again, if he is to save himself from disaster.