Sometimes cavalry are able to take the enemy's artillery unawares, or fall upon his infantry while it is in disorder. When this happens, their charge is very effective; guns are captured, and the infantry is dispersed. If, however, infantry keep cool and collected, have plenty of ammunition, and can see the mounted men for some minutes before they arrive at close quarters, they can shoot down horses and troopers, and probably save themselves from being ridden over. Cavalry has its best chance of success when it suddenly attacks infantry from a flank, and at the same time is secure from being taken in _flank_ by the fire of other infantry or machine guns. When cavalry are called upon to charge, they do so in a line of two ranks, with the officers riding in front. Sometimes cavalrymen fight on foot, much as infantry do. * * * * * Now let us learn something of the guns and the men who work them. The gunner's weapon is simply a big rifle, very thick as compared with its length, and so heavy that it has to be hauled along by horses or motors. Guns meant for use in the field are mounted on a two-wheeled carriage. When the gun is in action the end of the trail or steel beam at its rear rests on the ground. On the march this trail is lifted up and hooked on to another two-wheeled carriage, called the limber. The four-wheeled carriage thus formed is drawn by six horses, driven by men riding on three of them. Along with every gun there are two carriages for transporting the shell and shrapnel which are fired from it. Field guns are of various sorts and sizes, according to the work which they have to do. Our Royal Field Artillery is armed with a quick-firing gun, called an eighteen-pounder, because it throws a shot weighing eighteen pounds. This gun is made by winding strong ribbons of steel round a long steel tube. It can throw its charge for about three and a half miles, but it is most effective when the range is not more than about two and a quarter miles. Most of the guns fire shells which are shaped like bullets, but are, of course, very much bigger. They consist of a hollow steel case, with rings of soft copper, some of which fit into the rifling or grooves of the gun. The shell, like the bullet from a rifle, is given a spinning motion by the grooving in the barrel, and this makes the shot travel point foremost. Inside the shell there is a high explosive. When the shell reaches its target this substance explodes with such terrific force that it will smash a wall, a house, or an earthwork. [Illustration: Shrapnel Shell. (Section.)]