For battering down fortresses very heavy howitzers are brought up. The Germans have reserved as the surprise of this war a howitzer with a calibre of seventeen inches, which throws a huge weight of metal for a tremendous distance. The gun is so heavy that it is provided with caterpillar wheels, and is hauled by motor or by thirty-six or forty horses. It is fired by electricity, and it is said that the gunners stand four hundred yards behind it when it is discharged. [Illustration: Armoured Train. (_Photo, Central News_.)] Guns for firing high at aeroplanes are also used, and some of them are mounted on motor cars. On the railways naval guns are placed on armoured trains, which dash along the line and harass the enemy. Armoured motor cars are sometimes provided with machine guns, but these belong to the infantry, and not to the artillery. Now let us see what part artillery plays in a modern battle. Its first object is to help the movements of its own infantry, and to harass the movements of the enemy's infantry. Guns are thus the handmaids of infantry. Almost every modern battle opens with what is called an artillery duel. The guns of the one side engage those of the other, so as to keep them busy, and prevent them from hampering the movements of the infantry when they are forming line of battle or are advancing. [Illustration: Columns marching along one road and deploying.] Infantry march to the battlefield in columns, one behind the other; but before they can attack they must _deploy_--that is, unfold, open out, and extend into a line so as to face the enemy with their full force. Suppose the six columns, from A to B, are marching along a road, and are required to attack. They must "deploy"--that is, march as shown in the figure to take up the positions indicated by the dotted blocks from E to F. I need not tell you that the deeper the columns are the longer they will take to deploy. A general, therefore, tries to choose a line of advance where there are many more or less parallel roads or railways leading in the desired direction. When his troops move in this way his deployment may be very rapid (see figure below). This is one reason why the Germans violated the neutrality of Belgium. They wished to have as wide a front as possible to advance their troops into France.