As soon as it was fully realized that mustard gas persisted for several days it was decided to run complete reliefs of men into and out of areas that had been heavily shelled with mustard gas, or better still, where practicable, to completely evacuate the area. Inasmuch as the gas is dangerous to friend and foe alike, this method was comparatively safe and was used to a very considerable extent. With the warfare of movement that existed over most of the active front throughout the season of 1918, this moving of troops out of infected areas became highly important and, when skillfully done, often resulted in a great saving of troops and at the same time prevented the enemy from receiving any particular tactical advantage from his mustard gas attacks.
There was one very excellent example of this a few miles to the northwest of Château-Thierry prior to the counter-offensive of July 18, 1918. At that time the Germans heavily shelled with mustard gas four or five small woods and two or three villages. It was necessary for the men to stay in these woods during the day, as they afforded the only protection obtainable from machine guns, shrapnel and high explosive. At the time this occurred American gas officers generally understood the necessity of getting troops out of a mustard gas infected area. Accordingly all began searching for places safe from the mustard gas. In one particular instance the gas officer of a regiment discovered that a portion of the woods his men were in was free from the gas, and the regimental commander, promptly following his advice, moved his troops into the free area. As a result of this prompt action the regiment had only four light gas casualties, although all told there were several hundred mustard gas casualties in this attack, the number per thousand generally being from ten to twenty times that of the thousand men just mentioned.
Mixing Poisonous Gases
On this as well as other occasions the Germans fired some diphosgene and Blue Cross (Sneezing gas), as well as mustard gas. This added to the difficulty of determining areas free from the latter. In the future such mixing of poisonous gases may always be expected and, in addition, gases which have no value other than that of masking the poisonous ones will be fired. While with practically all gases except mustard gas a man is comparatively safe while breathing a concentration very noticeable to the sense of smell, the only safe rule with mustard gas is to consider as dangerous any concentration that can be smelled.
For the reason that this gas persists longer in calm areas, woods are always to be avoided, where practicable, and also, since all gases, being heavier than air, tend to roll into depressions and valleys, they should be avoided. There have been a number of authentic cases where batteries in hollows or valleys suffered severely from mustard gas, while troops on nearby knolls or ridges were comparatively free, though the difference in the amount of shelling of the two places was not noticeable.
Of great importance with all gases is the posting of a sufficient number of sentries around men sleeping within the range of gas shell. The worst projector gas attack against the Americans was one where the projectors were landed among a group of dugouts containing men asleep without sentries. The result was a very heavy casualty list, coupled with a high death rate, the men being gassed in their sleep before they were awakened.
Destruction of Mustard Gas
Prior to the introduction of mustard gas all that was necessary to get rid of gas was to thoroughly ventilate the spot. Thus in trenches and dugouts, fires were found to be very efficient, simply because they produced a circulation of air. In the early days, among the British, the Ayrton fan, a sort of canvas scoop, was used to throw the gas out of the trenches. While this was taken up in the American Service, it did not become very important, since it was found that, under ordinary atmospheric conditions, natural ventilation soon carried the gas out of the trench proper, while fires in dugouts were far more efficient than the fans. Likewise the Ayrton fan smacked too much of trench warfare which had reached a condition of “stalemate”—a condition that never appealed to the Americans and a condition that it is hoped never will.
With mustard gas, however, conditions were entirely changed. This liquid having a very high boiling point and evaporating very slowly, remains for days in the earth and on vegetation and other material sprinkled with it. This was particularly true in shell holes where the force of the explosion drove the gas into the earth around the broken edges of the hole. While many substances were experimented with, that which proved best and most practical under all conditions, was chloride of lime. This was used to sprinkle in shell holes, on floors of dugouts and any other places where the liquid might be splashed from bursting shells. It was also found very desirable to have a small box of this at the entrance to each dugout, so that a person who had been exposed to mustard gas could thoroughly coat his shoes with it and thus kill the mustard gas that collected in the mud on the bottom and sides of his shoes.