Another type of gun which is used in the field is called a _howitzer_. The great difference between the action of an ordinary gun and that of a howitzer is the difference between a boy throwing a stone at a mark which he can see and the same boy pitching a stone over a wall so that it will fall on something hidden from his view. The ordinary field gun has a long flat sweep of fire, and is therefore unable to shoot over hills, trees, or houses, or to drop shells on men lying close beside a bank or in a deep, narrow trench. Field guns can burst their shrapnel so that such men would not dare to look over the bank in front of their trenches and aim their rifles at the enemy, but they cannot actually hit the men in the trenches. In order to do this, the shots must be thrown high into the air, so that they will drop straight down on the trenches. Howitzers are used for this purpose. They are so made that the barrel can be tilted and the shots fired at a high angle. [Illustration: Heavy German Howitzer for siege work. (_Photo, Newspaper Illustrations._)] [Illustration: The left-hand picture shows the advantage possessed by a howitzer over a field gun when firing over a hill at some troops at T. I is the howitzer, and _a_, _a_, _a_ is the track of its shell. 2 is the field gun, and _b_, _b_ would be the path of its shell were it not stopped at B by the hill. The right-hand picture compares the effects on a trench of a shell from a howitzer and a shell from a field-gun. 3 is the howitzer's shrapnel shell bursting and pouring its bullets into the trench; but you will notice that the parapet of earth protects the occupants of the trench from the bullets of the field-gun's shrapnel shell, which is bursting at 4. Both of these shells are fitted with "time fuses," which make them explode in the air as shown. If they were fitted with "percussion fuses," the howitzer shell would fall to the bottom of the trench, and explode at H; while the field-gun shell would not burst until it hit the ground at S. In both pictures the howitzer is firing at a range of 2¾ miles--that is, it is 2¾ miles from the target--and the field gun at a range of 2¼ miles.] You can easily understand that howitzers are very useful when troops are advancing on the enemy. They can be fired behind the advancing line, for the shots from them fly high over the men's heads. Ordinary guns cannot be used at such a time, for they must be in line with the infantry or in front of them. These guns are usually held in reserve until the enemy shows himself. Then they are brought forward, and open fire. The barrel of a howitzer has a wider bore than that of a field gun, and its shell is not so long. The 5-inch howitzer with which the Royal Garrison Artillery is armed is so heavy that eight horses are needed to haul it along good roads. When it is taken over broken country the team must at least be doubled. Six-inch howitzers are also used.