Meanwhile other factories were springing up for the purpose of making explosives while others again were erected for producing the acids and other chemicals necessary for the explosive works; and yet another kind of works, the filling factories, came into being as if by magic and thousands of girls flocked from far and near to these places, there to fill the shells with the explosives.
Even the soldiers did not realize a few years ago how important the supply of shells was going to be. The rifle has fallen from its old place of importance while the gun and the shell have risen to the first place.
What, then, is a shell? It is what its name implies, a case covering something else, just as the shell of a fish covers its owner. It is a hollow cylinder of steel with certain things inside it. Its chief function is to hold these other things and to be shot out of a gun carrying them with it to their destination. You want to cause an explosion in an enemy's ship. You cannot get near enough to put the explosives there by hand, for he will not let you, so you put them into a steel shell and then hurl the whole thing at him out of a gun.
Bomb Throwing.
One of the most striking things about the war was the re-invention of the bomb thrown by hand. This officer hurled bombs at the enemy for twenty-four hours continuously.
In the attempt to prevent your doing him any harm by thus throwing boxes of explosives at him, the enemy clothes the sides of his most valuable and important ships with thick steel plates, wherefore you have to make your shell strong and tough so that it shall not splinter against the armour but shall on the contrary bore its way through, finally exploding in the interior of the ship.
If it is not a ship that you are attacking but, say, an earthwork or an arrangement of trenches, then you do not need to penetrate steel armour and your shell can be thinner and of lighter construction. It still needs to be strong, however, for it has another function besides simply carrying the explosive. It must hold the force of the explosion in for a moment while it gathers force so that when the hour comes the pent-up energy may strike all round with the utmost violence. Even the most powerful explosives are comparatively feeble if they go off in the open. By holding them in check for a moment and then letting their force loose suddenly you get a much more forceful blow.
Shells which contain only an explosive are called common shells or high-explosive shells. Shrapnel shells constitute another type in which the force of the explosion is simply employed to release a number of round bullets, which strike mainly because of the velocity which they derive from the original motion of the shell. These are above all things man-killing shells, for their result is akin to a volley of bullets at close range.