"But, as you said yourself," protested the boy, "a cloud of gas passes over, and then it's gone."
"I said it used to be that way," the sergeant-major answered, "but it's not that way any more. The Germans don't send their gas from big fixed gasometers now; they have tanks which a man can carry on his back and from which the gas is jetted by compressed air. Infantry, with gas-masks on, can come right up behind the men carrying the gas tanks and, just as soon as the heavy poison fumes begin to fill the trenches, they charge."
"Isn't there any way of stopping it?"
"Only with a fearful amount of trouble and enormous expense. Poison gas, being heavier than the air, sinks. To keep it from sinking, then, you have to create a strong upward air current. Any bonfire will do that. If, when a cloud of gas approaches or when men carrying gas reservoirs approach the trenches, you can start a bonfire every few yards along the line, the poison gas will be sucked into this up-draught and dispersed by the heat. That has been done, several times, and it was the only defense of the British at Ypres, before the gas masks were hastily improvised. But that means hauling a lot of fuel to the front, and every pound of fuel transported means a pound less of provisions and munitions. Besides, as soon as we worked out that kind of defense, the Germans schemed a new way to use the gas. Now they put it into shells by compressed air. They have two of these gas shells which they call the 'T' type and the 'K' type."
"How do we know what they call them?"
"Because those letters are painted on the ogives of the shells. The 'T' shells are filled with a very dense gas, which disperses slowly. After a storm of these shells has fallen, the air is unbreathable for an hour or sometimes two, according to the dampness of the weather. The 'K' shells are filled with a more powerful spasm-gas, virulent in its effects, but which disperses rapidly.
"The first is used in curtain fire, when the Germans expect to be assaulted. A steady dropping bombardment of 'T' shells makes a gas-filled zone. Charging troops have to wear gas masks, for they must pass through it. Defending troops do not need to wear masks, and, as you know yourself, a man is twice as quick and agile without a mask.
"The second, or 'K' shell, is used when the enemy plans to make the assault. You can't see the shells coming, there is no evidence of any change in the enemy's lines which can be reported by an aëroplane. No one knows when the German artillery has received orders to change from high explosive or shrapnel to gas shells, when, suddenly, all along the line, there drops a concerted hail of gas shells, and in ten seconds half the men in the first line trenches are gassed. It takes about twenty seconds to put on a gas-mask properly. It is a horrible, vicious, and cowardly way of making war."
"But don't we use it, too?"
"We haven't yet," the veteran answered, "but we shall have to begin soon, in self-defense.[23] Then the Boches will be sorry that they began, for their own atrocious cruelty will return on their own heads. But we have a new invention, too, which is gaining us more ground than we lost by the poison gas."