We see some soldiers urging the horses to pull one of their heavy iron cannons along a difficult road, and we tell the General that even his heavy gun is as a plaything compared to what will be in use in the twentieth century. We can imagine the old-time General saying that if we are going to have such giant guns we shall require giant men to work them and giant horses to pull them along. We could not blame the General of these days if he should say that the thing would be impossible. He could not know anything of the mechanical appliances which were to be invented, and how by the mere moving of a hand-lever the great gun could be made to turn about just as desired. He could not guess that one day we should have motor-cars which, without the energy of men or horses, could carry far heavier guns than his from place to place.

The particular twentieth-century gun of which we were thinking during our imaginary conversation with the old-time General was the famous Skoda mortar of the Austrians. You will see a photograph of it facing this page. Look how it seems as though it were about to shoot at the moon. I think you will be able to guess why it is aiming so high, but we shall have a talk about that later on. Meantime we wish to see what this giant gun can do, and how easily it can be handled.

We are very sorry that the gun was an invention of the enemy. It was this kind of gun which made it impossible for the French to hold the forts of Liege and Namur, and other strong fortifications in the Great European War. And it was such guns as those that forced the brave Belgians out of Antwerp. Of course there are giant British guns as well, but this enemy gun was very prominent in the Great War.

Our old-time General would never have believed us if we had told him that this giant gun would be able to hit and destroy any particular building that was desired even if the building were many miles away. You remember how erratic was the flight of the solid iron ball fired from his old cast-iron cannon.

We may not think less of the Austrians because they invented such a murderous weapon of war; we have been trying at all times to do the same. Why we thought very hard things of our enemies in the Great War was because they would not abide by the rules of warfare to which they had previously agreed. But what we set out to talk about was the Great War inventions, and this Austrian Skoda mortar is one of the most remarkable.

In the Austrian Army Museum in Vienna there is exhibited a cupola of a building with part of a great shell still embedded in it. The Austrian guide would be proud to tell you that this cupola was brought all the way from Antwerp, because it was a proof of the great accuracy of their famous giant guns.

This cupola was in a building which it was desired to destroy, but the great gun could not get nearer than 7 miles, and from that position the gunners could not see the building at all. Very careful measurements were made from a map on which the building was shown, and the muzzle of the great gun was directed so that it might land a shell on that particular building which was invisible to the gunners. A shell weighing more than 800 pounds was placed in the gun, and it flew through the air for 7 miles, and landed right through the cupola of the building which the gunners desired to hit. No wonder that Antwerp, although the second strongest fortified place in the world, had to give way to such guns.

The remarkable thing was how very quickly the enemy could bring forward these giant guns, and how little time it required to remove them to another place. The reason was that three special motor-cars of 100 h.p. each were able to carry the gun, the mount and the foundation. It is usual to dig a pit for the foundation, and the car carrying the foundation platform is brought forward and the foundation is lowered into position by a crane or winch carried on the car itself. Then the car carrying the mount drives up and goes right on to the foundation, on which the mount is lowered and securely bolted. Then the third car brings the great gun forward and it is pulled into the cradle. All this has been done in twenty-four minutes, and can be done in almost any circumstances in forty minutes.

When the gun is to be loaded it is not pointing upwards, but straight along in the position which we describe as horizontal, as it points towards the horizon. The great breech-block is then opened on its hinges to allow the shell to be loaded in the gun. You will observe one of these shells on a small truck in the photograph facing page 64. By moving a lever the loading-pan raises the heavy shell into position, so that it can be easily pushed into the breech of the gun. The breech-block is then closed, and the gun again is pointed upwards as shown in the photograph. The exact angle at which it points is, of course, dependent upon the distance the shell is required to travel before coming to the ground. When we come to have a talk about the naval guns we shall see that we have made guns that are even greater than this Skoda mortar, but the remarkable thing about this Austrian invention is the ease with which it can be moved about from one place to another.

After the outbreak of the Great War we were surprised to find that the enemy were using a still greater giant gun, which was able to throw deadly shells into a French town (Dunkirk) from a distance of 22 ½ miles. Imagine what a tremendous explosion must be required to throw a heavy shell so many miles.

An aeroplane can travel a very long distance, because it carries an engine and propellers which keep driving it along. The shell, however, has no means of keeping itself in motion. It has to be thrown all the way by the gun. You know that when you are throwing a stone you must send it off at a great speed if you wish it to travel far, but by the time it reaches the distant object it has not much energy left, and falls down exhausted of all energy. If you wish to throw a stone far, you select a fairly light one. You cannot throw a heavy stone far, because you cannot give it the necessary speed or velocity at the send-off. Imagine then what a tremendous velocity must be given to a heavy shell which, after leaving the muzzle of the gun, has to continue flying through the air for more than 20 miles. The shell sets off with the enormous speed of 2000 miles per hour.

The giant gun which threw shells at Dunkirk from a distance of 22 ½ miles was what we call a 16 ½-inch gun. One boy might tell another that he had a 2 ½-inch cannon, and his friend would know that the cannon measured 2 ½ inches in length. But when we speak of a 16 ½-inch gun, you don't imagine that we are referring to its length. We are speaking of the size of its bore. We say that that is the diameter of the bore, which is another way of saying that the open muzzle measures 16 ½ inches across. This also tells us the diameter of the shell which the gun is to shoot.

We used to speak of a 68-pound gun, meaning that it threw a shell weighing 68 pounds, and we also spoke of a 110-ton gun, which described the weight of the gun itself, but nowadays we always describe a gun by the diameter of its bore. This great 16 ½-inch German gun is not so easily moved about as the 12-inch Skoda mortar of the Austrians. The great giant has to be firmly embedded in solid concrete before it can be used, then when it is desired to remove it to some other place, it is necessary to blast the concrete with explosives in order to get the gun free.

You are sure to have heard of the famous "75" guns of the French, for those guns did terrible havoc amongst the enemy in the Great War. You will see a photograph of one of those famous guns in the illustration facing page 72. It is not such a giant as its name might lead you to think. Most of you could guess to what measurement the 75 refers. Being a modern gun, you will know that the figures describe the diameter of its bore, and it is quite evident that the opening of the muzzle does not measure anything like 75 inches. One boy suggests that it is 75 centimetres, but he forgets how much the centimetre is, or he would know that 75 centimetres is about 29 inches, and it is quite evident from the photograph that the bore is very much less than that. Then he guesses it is 75 millimetres, and he is correct this time, and if he understands the French measurements he will be able to tell you that the bore of the gun is somewhere about 3 inches in diameter.

Looking at the photograph opposite page 72, you will see that the gunners have removed the breech-block in order to give their gun a thorough cleaning. You will also see, in the left-hand corner, a store of the shells used in this gun, and you see from this that the diameter is just about 3 inches.

You might say that these 75-millimetre guns are not really giants. They are not of gigantic size, but they can do gigantic deeds, for they fire shells which carry high explosives into the midst of the enemy. A French writer has said that they create a danger zone "in which nothing before living can any longer live." When the signal is given that the enemy is advancing, these guns are quickly brought into action. The plan of their operations is not unlike what you would do with a hosepipe if you were watering the garden lawn. Four guns, acting as a battery, sweep the ground in front, so that they cover the whole area before them. Then the muzzles are raised very slightly, and the guns sweep across the new area, and so on, until a dozen acres have been cleared of the enemy.

There are many giant guns in the Navy, and instead of requiring giants to work these, we have merely to move small levers which control the guns. The old-fashioned heavy cannon called for a great expenditure of energy on the part of the gunners. After the ship's cannon was fired in the primitive manner already described, the crew had to pull the muzzle of the gun in with ropes to clean the barrel and recharge the gun. Even the heaviest guns had to be loaded by hand. We could not handle our modern guns in the same fashion, and there is no need to do so.

Suppose we pay an imaginary visit to one of our great battleships and see for ourselves how the giant guns are handled. We are told that the largest guns on this particular dread-nought are 12 inches, and from this you know that the bore of this gun is 12 inches in diameter. We notice that these guns are very long, and we are told that they measure 50 feet in length. We climb a ladder on to the roof of the great iron turret in which the gun is placed, and going down from a cupola or trap door we enter the turret. Here we see the gunners and the levers which control the hydraulic and electric power required to move the great guns. But how are the men to handle the shells which weigh 850 pounds each? And then behind the shell is to be placed a charge of cordite weighing 350 pounds. Therefore each loading of the gun means lifting 1200 pounds, which, you know, is more than half-a-ton.

We watch a pair of automatic rammers pushing the shell and the charge of cordite from a cage into the breech of the gun, but we can see no more shells and cordite charges about. Where are these kept?

We go right down within the turret to the lower platform, and there we see the stock of shells. We watch a grab mounted on rails lifting one shell from the stock and placing it on a travelling tray, which carries it to the cage of a hoist. While this is being done at the lower platform, the cordite charge is being placed on another cage of the same hoist at the upper platform, which is immediately above the lower one. Then the hoist lifts this double cage to the gun-room, where the shell and cordite are transferred to another double cage, which carries them to the breech of the gun. We have already seen how the two automatic rammers push the shell and then the cordite into the breech of the gun.

One boy remarks that when the gun is turned round in another direction it will not be in a position to take advantage of the hoist and these automatic rammers. But that is not the case, for the whole turret in which this mechanism is contained turns round along with the gun; it is the turret which revolves, carrying the gun with it. These large guns are usually fired electrically, and may fire two rounds in one minute. Each shot costs £100, and the gun with its mechanism costs about £12,000.

One boy asks what advantage is gained by having the gun so long as 50 feet. It is in order to take advantage of the full pushing power of the explosive. While travelling along the barrel of the gun the shell gets a long push off. But the boy says that the giant mortars throw shells to great distances, and yet they are not nearly so long. That is so. But in the mortar a higher explosive is used, causing a more violent explosion, which we do not wish on board ship.

The Queen Elizabeth's  guns can throw one-ton shells to a distance of 24 miles. In the illustration facing page 112 you see this super-dreadnought in action.