Gas and flame in modern warfare

by Samuel James Manson Auld

To get over this difficulty the Germans fitted their cylinders with internal siphon tubes so that actually liquid chlorine was forced into the air, where it evaporated without affecting the gas remaining in the cylinder. By this means the whole of the gas in the cylinder, amounting to forty-five pounds, is emptied into the atmosphere in less than three minutes. The sudden expansion of the chlorine in the air also makes both it and the surrounding air cold and helps to keep the cloud close to the ground.

The actual handing of the gas attacks was allotted to two regiments of pioneers—the 35th and 36th Pioneer Regiments, which were specially organised for this purpose. These regiments have the ordinary organisation of two battalions per regiment, with three companies and a park or transport company per battalion. The rank and file are ordinary pioneers, but the officers are specially picked and include chemists, mechanical experts, meteorologists, and other men with special scientific qualifications.

The choice of country in which to make a gas attack was a serious matter to the enemy. The gas of course will go with the wind, but it depends largely on what the country is like where the wind will go. The Germans themselves say they prefer a flat country without any marked under features and sloping gently toward our lines, just as they had at Ypres. Indeed, they went the length of saying that a gas attack could not be carried out in hilly or very broken country; and they suffered in consequence later on, through being taken unawares by the French in just such country in the Vosges when retaliation was commenced. But taking it altogether the Germans were wise in their choice of position.

Another thing that had to be considered was the outline of their own trench system, so that they would not let off the gas in such parts of the line that it would float back and gas their own troops in the neighbouring trenches. To do this they invented a “factor of safety,” which represented an angle between the direction of the wind and the line of the trenches. No attack was to be made if the wind direction came within forty degrees of any trench within gassing distance. This worked very well.

Another consideration was the strength of the wind. The wind must not be too strong when the gusts disperse the gas cloud, or it will weaken it so that it loses a lot of its effect and will be blown over the enemy too quickly; nor must it be so weak that it will take a long time to reach the opposing trenches.

Another great danger in winds of too low velocity is that these are just the winds which change their direction most frequently, and anything under two miles per hour is just as likely to blow the gas back to the place from which it came. It was disregarding this principle on one occasion later on that caused the Germans numerous casualties from one of their own gas clouds. In general, however, it may be laid down that the most favourable winds are those between four and twelve miles an hour, so that with a wind of eight miles an hour the cloud would move just twice as quickly as a man walking rapidly, and would take only twelve and a half seconds to cross No Man’s Land in places where the trenches are fifty yards apart.

Let me try to give an account of the procedure of carrying out gas attacks as it was told me by a German prisoner taken not so very long ago. He said:

“I am not one of the gas pioneers, but being an engineer by trade and having been in the trenches for many weeks with the 35th Regiment of Pioneers I have got to know their methods fairly well. Indeed I assisted on one occasion in carrying cylinders into the trenches for an attack against the British. Gas is not popular with us; we have had too many mishaps, and the cylinders are a nuisance to carry into the trenches. They weigh ninety pounds and they are always carried in by the infantry. A gas regiment does not do that for itself. It is a long carry and it is really more than a one-man load. At the most two men are allotted to carry in each cylinder, whatever the distance.

“Several thousand of these cylinders must be taken into the trenches, and then we have the job of putting them in position. Deep holes are dug just underneath the parapet of the trench, and into these holes are placed the separate cylinders with the tops flush with the ground. As each cylinder is placed into position the hole is covered with a board, on top of which is placed a thing we call a ‘Salzdecke,’ which is really a kind of quilt stuffed with peat moss and soaked in potash solution so as to absorb any of the gases that may leak out.

“On top of the Salzdecke are built up three layers of sandbags, so that there is not much danger of the cylinders’ being hit by shell fragments. This also serves to hide the cylinders in case a raid is made, and the sandbags form an excellent firing step. In fact, you would never guess that the gas was ready in position to make an attack. All of this takes a long time to do, and then we have to wait for a wind that is favourable.