At one time many people wondered why the Germans did not put some of these huge mortars on their battleships: many thought that they would do so, and that by that means they would demolish our navy as they had already smashed the Belgian forts. The reason they did not is, no doubt, the very simple one, that our naval guns would have probably sunk their ships before the howitzers could have reached ours, because if they had attempted to make up for the shortness of the weapons by using higher explosives, these mortars would, there is little doubt, have knocked to pieces the ships on which they were mounted. The old-fashioned fortress, suddenly made "out-of-date" by the Skoda mortars, was usually armed with guns of the naval type. Sea-coast forts are always so armed. Nowadays, however, the inland fortress takes the form of a labyrinth of trenches and underground passages, combined with deeply excavated chambers known as dug-outs, and these do not fitly accommodate large guns at all. The guns are placed well back behind the trenches sheltered behind hills or woods, over which they hurl their shells. The chief defenders of the actual trench are the machine gun, which is little more than an automatic rifle on a stand, and the trench mortar. We are now in a position to sum up broadly the features of modern artillery. There is first the naval gun, the ideal gun, long and of great range, able to send forth its shells with great velocity. This gun appears again in the sea-coast forts, where the conditions are very much those which obtain on a ship and where the attacking party is of necessity a ship. In the field we have the field and horse artillery, which we may regard as the naval gun modified somewhat in order to make it easy to move about, so that it can accompany troops and support the operations of both infantry and cavalry. These light guns are supported by the field howitzers, which are also light and easily handled, and the guns of the 4·7 type, originally naval guns but now mounted on wheels and possessing a certain amount of mobility, not equalling the field guns it is true, but still very serviceable in a campaign. Then we have the howitzers of various sizes which have rendered the old-fashioned steel and concrete forts useless, and which are the chief weapons used in the modern trench warfare. It is these which blow in the walls of the trenches and dug-outs, shatter the barbed-wire entanglements and render it possible for the infantry to attack an entrenched position. Finally, we have the machine guns, each of which is equivalent to a considerable number of riflemen and which, with the trench mortars, form the chief defences of the actual trench itself. Of course these are only useful against attacks by infantry: they cannot in any way cope with the heavy artillery. That has to be dealt with by the opposing artillery posted away back behind the trenches.