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Mal Wright Fezian writes:

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24 July 2008page first published

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Mal Wright Fezian writes:

The importance and use of chemical warfare in WWI and its application to tabletop wargames

Soldiers advance through gas clouds

Most wargamers are unfamiliar with the chemical weapons of WWI. Many have quite incorrect ideas of what they did and did not do, so I have penned this article to help those wargaming that era to better understand this kind of weapon, its values and its limitations.

We can class WWI gas weapons into three categories for the purpose of our discussion:


Phosgene, Diphosgene etc. German Green CROSS, Green CROSS +, Green CROSS ++, Green CROSS +++

Non-toxic war gas, such as tear gas, sneezing gas, breath restrictors.
Medical effect:
Eyes, Nose, Throat, vomiting, shortness of breath causing panic.
Military effect:
These were the most commonly used war gases.

Always artillery-delivered. Issued at all levels, and can be a battery commander decision to use them. Usually part of Divisional or Corps attack or defense plans. Extensively issued weapons type.

They are rarely toxic, but of course only veterans would realize that - and even they would not feel entirely safe, as it is hard to tell one gas from another. These gasses are fairly heavy, so they usually gather in low, dense clouds, and penetrate even into underground bunkers that are not protected by gas blankets. Although the clouds are densely gathered, they are not always completely visible. Troops can blunder into dense gas concentrations and be overwhelmed before being able to get their masks on.

There are several reasons why they were the most commonly used:

  • Cheap and easy to produce
  • Relatively easy to deliver by shellfire
  • Not so dangerous for the firers and shell primers to handle
  • Temporary effect does not stop your own side occupying the area afterwards
  • Because it gathers in clouds and seeps down, it can force the enemy out of their bunkers, making them more vulnerable to normal artillery HE
  • It can force less experienced troops to seek shelter from it by leaving their trenches
  • They force the enemy to wear gas masks
  • They confuse the enemy
  • They severely effect the ability to fight without a gas mask (close to total)
  • They seriously effect the ability to fight, because of the need to wear a gas mask
  • They seriously effect the visibility of the enemy, because of the need to wear a gas mask
  • They add to the fatigue of the enemy, because of the need to wear a gas mask
  • They annoy and wear down the enemy, because of the need to wear a gas mask
  • The need to wear a gas mask severely affects communications - voice commands, telephone, visual
  • Regardless of troop class or experience, the need to wear a mask is universally hindering

Endurance. These gasses, if delivered effectively, will force the enemy to wear gas masks for up to three hours in trench situations, gun pits, etc. Up to 12 hours in ruins, woods, crops.


Chlorine, Vincennite, Arsenic Trichloride, Hydrogen Cyanide, German Blue Cross, German White Band

Very toxic war gas, intended to kill
Medical effect:
Lungs damaged, eyes damaged, breathing causes death or serious permanent illness
Military effect:
These were the most commonly used war gases in the early war period. Very toxic; kill effectively if delivered in dense clouds; light and easily wind blown. Limited-issue weapons type.

These were mostly delivered via gas cylinders. Their use would be a decision at Army level or higher. Used for attack only.

Main means of delivery is simple: Gas cylinders are taken to the attack area. Usually a second trench line, but sometimes the front trench. Attack area is a specific one, and usually half a mile or so in width. When the wind is right, all troops in front of the cylinders withdraw. The cylinders are opened and the gas released.

The gas drifts with the wind onto the enemy positions. If the wind is slight, it will have the greatest effect as it will remain dense and stay around longer.

The effect of being caught in it, without a gas mask, is immediate difficulty in breathing. The victim is forced to vacate the area (if he can), and if not, will die fairly quickly. If he can vacate the area it will have to be rapidly, therefore in panic. Its effect is the same on troops of all classes - if you can't breath, you are dead; being a veteran or inexperienced soldier is of no consequence if you are unprotected.

Second means of delivery: shellfire. This was found to be mostly ineffective, as it was almost impossible to concentrate enough of it to form a dense cloud. It also burns off, so HE and exploding shrapnel rounds could not be effectively deployed at the same time, in order to take advantage of the troops leaving cover. Its overall effect was therefore much the same as Irritants. As it was much more expensive to produce and far more dangerous for the crews to handle, it was quickly abandoned in favour of Irritants.

Users. Commonly thought to be a German weapon, in actual fact the Allies were in a better industrial condition to produce and use it. They persisted in its use long after the Germans had abandoned it.

The British launched it in massive 'beam' attacks. This involved bringing a light railway load behind the front line. At the given hour (always at night), those in the trenches fell back behind the light railway. The cylinders were then opened and a huge, dense cloud drifted across the front-line trenches, over no-man's land and over the enemy positions. It was so dense (they chose the weather carefully) that in the concentrated area (a few hundred yards wide), anyone without a gas mask would be killed. Those who put masks on would still be forced to leave the area, because the gas was so dense they could not be sure their mask filter would last long enough. The cloud was so dense that it would continue to drift well into the rear in concentrated clouds, and often caught and killed enemy troops asleep in their billets.

The gasses chosen were selected because they did tend to hang in clouds and were not too easily dispersed by light winds. They would not be released in stronger winds.

Military Use: Toxics were originally used as a pre-attack weapon. The disadvantage was that the attackers had to wear gas masks, placing the same visual, communication and movement restrictions on them.

Their later use, such as beam attacks, was to kill and shake morale, often on the flanks of an intended attack. Their use by the Allies was only abandoned after the front had become less rigid. It was, of course, almost impossible to deploy unless the enemy frontline was in a fixed and concentrated position. It remains an option for British troops, in particular, right into early 1918.

Endurance. Only for as long as it took for the cloud to pass over. It was light and wind-blown. It did not seep downward. Once it had passed, you were perfectly safe to remove your mask. Generally most masks could last 20 to 30 minutes without a change of filter. This was more than enough.

The only variation on this was British Beam attack gas which could seep into some lower areas, being a heavier gas. This was selected to enable the 'beam' to last for a long distance before it was dispersed, and to resist wind dispersal.

When delivered by shellfire, the gas dispersed very quickly. If the weather was too cold, it would freeze and sink to the ground (occasionally reforming when spring came). It also dispersed in hot climates. This made it very difficult to use as an artillery weapon.

Overall Effect. Deadly in the early war period. Much less so later, provided troops had gas masks. If not, it was a killer. The effects were usually panic at the loss of breath, followed by attempted flight, followed by death. The quality of troops had little to do with it if they had no masks. A crack guardsman will panic just as much as a green soldier, if he cannot breath.

Once effective masks were provided, the overall effect was limited to the unwary. When first encountered it had the effect of causing panic, or at least great fear. With a mask on, troops would still be worried, because even a shrapnel tear in the mask could let in a fatal dose.


Allied Bromenzylcyanide, Camite, Yperite. German Yellow Double Cross. Commonly known as Mustant Gas.

This is, in fact, not a gas at all. It is a chemical warfare agent - but in the terminology of the trenches, it was another rather nasty gas weapon.

Highly toxic chemical agent with ability to cause tissue damage
Medical effect:
Eyes, causing temporary blindness. If inhaled, will usually result in death. If contact with the skin, large blisters and painful irritations.
Military effect:
Denial to enemy (and self) of effected area. Forces enemy to leave (or not pass through) area. Troops remaining in area require heavy protection, with resultant loss of combat effectiveness.

Always artillery-delivered. Usually part of Divisional or Corps attack or defense plans. Widely-issued munitions type. A late-1917 weapon in some cases, but in general issue during the last half of 1918.

There are several reasons why this agent was used:

  • It can be put down on the units flanking a proposed attack. That will not only cause them to vacate those areas, but make it very difficult and costly for any troops to move through it, in order to threaten your attack.
  • It can be put down on enemy artillery positions, forcing them to move away.
  • It can be put down on suspected enemy reserve marshaling areas, forcing them to chose other locations. Similarly it can be put down on areas suspected as being second positions for artillery, so that if they do have to move, they cannot go there, either!
  • It can be put down on enemy communications routes.
  • It can be put down on enemy rest areas.
  • It was difficult to counter, and its effects were just as deadly against a veteran as a recruit.
  • It was a morale buster.
  • In defense, it could be put down on suspected enemy jump-off points - forcing them to use others or cancel the attack.
  • It is liquid, and can get into cellars, bunkers, etc. It forms in the bottom of shell holes and trenches.
  • Because of the above, troops are forced out into the open. Enemy casualties are heavy if it can therefore be mixed with shrapnel and HE.
  • HE or Shrapnel does not burn it off. In fact, HE can help spread the droplets further.
  • The simultaneous use of HE and Shrapnel can result in the agent penetrating tears in uniforms, protective clothing, and masks, or creating wounds to let the agent in past protective creams.
  • It lasts for 72 hours. Up to 7 days in woods or ruins. (This can also be a disadvantage.)

There are several disadvantages to its use:

  • Your own side is just as vulnerable to it as the enemy, so the area is denied to you, too.
  • It lasts for 72 hours. Up to 7 days in woods or ruins.
  • It is no good for bombarding an area you intend to attack.
  • It is dangerous to handle.
  • It is dangerous to store.
  • In winter, it can freeze and come to life months later….and you don't remember where it was.

Exception. Although it was normally used as an area-denial weapon (through which the attacker did not expect to pass), during the Michael Offensive, some German Sturm Truppe were sent in to the attack through Mustard Gassed-areas. The reasoning was that this would be totally unexpected. It was unexpected, but not a success because although the assault waves were prepared for it, the follow-up troops were not as well trained and suffered serious casualties. Sturm Truppe losses were also too heavy to make it worthwhile. The mere fact that they were ordered to do it did not mean it was a good idea, only that the higher commanders who told them to do it were too ignorant of the difficulties. Therefore in a wargame situation, a player who orders his troops through such a barrage area should do so in the expectation of casualties.

So, How Does All This Affect the Wargame?


Obviously, this is mostly used in an attack, and even then, in a limited area of the front. Because it is Toxic, it had a fear about it. Most soldiers of the era were raised in the early era of gaslights and gas stoves, etc. They knew from civil life how explosions could occur by accident, but they also knew that being "gassed" was deadly. Many hundreds died in the early civil use of gas, through accident. It was so obviously fatal, that it became a popular way in which to commit suicide.

So to the common soldier, gas in the Toxic form was a very scary business, capable of killing all and sundry, with no distinctions for rank, class or troop quality. In this regard, it was therefore probably more feared than the overall results reflected. A grim British Army joke was that the stuff was so deadly, it could kill someone just looking at the paybook photograph of the victim.

In the wargames sense, it is not hard to deploy. It would be part of a pre-game plan, would be limited to a certain area, and would only be released if the wind was right. A simple dieroll can suffice to give wind speed, and the same roll determines how long the cloud remains together. The faster it moves, the stronger the wind, therefore the sooner it disperses. The charts you have already worked out are OK for casualties, except as below.

If the troops have proper masks and get sufficient warning, casualties will be light. The nuisance value will be high. Visibility is drastically reduced. Ability to move about and act strenuously is severely affected.

If they do not have masks at all, the casualties will be high regardless of troop quality. If they have poor or inadequate masks, the casualties will be less, but again will still have nothing to do with troop quality.

Ability to move about and act strenuously is not only severely affected, there is a strong likelihood the troops will abandon the area as a result of panic. The level of likelihood for panic is affected by troop quality….but how badly the equipment is functioning is also a factor. Therefore a guardsman veteran, with a poor mask, will choke at the same rate as a green recruit with the same sort of mask. Once a man starts to choke, his survival instinct cuts in. Breathing is one of the most basic of all human instincts to retain. Once he starts to choke, instinct takes over and the man will bolt for it, hoping to find some breathable air.

If the man is well trained and a veteran, and his equipment is functioning reasonably well, he knows that the attack will pass and is less likely to try tearing it off to get a breath, etc. This is the only value of higher troop quality.

After the first few months of cloud attacks, the casualties became quite slight. Everyone was scared and took precautions. The cloud attack then became not worth the expense.

With a beam attack, the concentration is so strong that it is very quickly fatal, and adequate warning might not be given. If that is the case, then along the path of its movement, casualties to men and animals will be heavy. They will also extend into the rear areas and supporting artillery, etc. - gas kills HQ troops just as easily as front-line troops. However, in this regard the HQ troops who have not served in the trenches may be at a disadvantage, as they are more likely to panic, and more likely to be slow to react to the danger.


Since it was quickly realized that the enduring advantage of a gas attack with Toxics was to make the other side wear gas masks, then a cheaper alternative was sought.

Pre-War, there had been experiments with tear gas. The French had used it to subdue some anarchists during a Paris siege. It was cheap to make and it affected both the eyes and breathing. Very few people could tolerate it, and so wearing a gas mask was necessary. The same applied to pepper-based gasses that made men sneeze, gasses that made people vomit, stung the eyes, etc.

In addition, unlike the cloud gasses, Irritants were reasonably simple to put into a shell. They were less dangerous to handle and less dangerous to store. They were also inexpensive, so plenty of ammunition could be provided. They exploded on the target area, and did not need to be in a cloud as they were re-enforced by following shells also landing on target. They had a reasonable 'hang around time' and were therefore very annoying for the target troops.

Advantages. An artilleryman forced to wear a gas mask can only work and fire at about half that which he normally would. His vision is reduced to a few hundred yards, and he gets tired very easy. Even if (as was usually the case) the artillery had spare crews, the fatigue level increased so much, so quickly, that soon all the men would be exhausted and the rate of fire drastically effected. The only choice would be for the guns to up and move to another position… or accept a slow rate of fire while waiting for the gas to disperse. You can't eat while it is around, you can't talk properly, and passing orders is hard. Using telephones (essential for artillery) is almost impossible. Draught animals must be masked or moved away. In the direct-fire mode (such as anti-tank), the men must peer through the vision slits of their masks, the smoke and debris of the battlefield, and the clouds of gas in order to see the target. For these reasons, much of the huge quantity of Irritants fired would be directed at the enemy artillery.

However, the next favorite target would be enemy machinegunners. With gas masks on, they too are restricted to a few hundred yards' vision. They get tired quickly, and with masks on are more likely not to see threats to their flanks…. therefore making them more vulnerable to advancing troops. They not only lose vision due to the restricted vision from their masks, they also lose vision due to the misty clouds of gas.

The next on the list were the front-line troops. These were less likely to receive as much of a thorough dousing with Irritants. Nonetheless, during the assault bombardment, they would be given sufficient to make them put their masks on. Sometimes this would be mixed with smoke, which was hard to distinguish from gas. As the troops did not know which was which, they would not take their masks off to sniff (and were not keen on this idea, in case it was real gas). So the effect was again to cause fatigue, to reduce visibility, and to make the men less capable of physical effort.

As none of the troops knew if the gas was Toxic or not, there was little chance they would leave their masks off and 'tough it out'. Gas was feared even by the bravest.

Even if they were stupid enough to try toughing it out, the effects of the Irritants would make them ill, their eyes and noses would be streaming, vomiting would be occurring, and the overall effect would be worse than wearing the mask, anyway.

A big advantage for the attacker was that the gas dispersed fairly easily. Therefore they could sneak up on the enemy trenches and assault from close range. To help with this, the artillery bombardment would switch to HE and smoke. As the defenders did not know when the bombardment was going to lift, they would not be able to tell the subtle difference…. and there would be a residue of gas about anyway.

Although the attackers might need gas masks initially, they would be able to take theirs off more quickly since they knew the schedule. With a mask on, a man cannot run, he can barely fight or do anything strenuous. The attacker, leaping into trenches without a mask on, has a great advantage. The defender 'could' take his mask off… but he is now too busy trying to repel the attackers.

Because of the easy dispersal, there was a good chance that troops breaking through would over-run rear areas, such as HQ and artillery support - and when they got there, would not need masks.

It had the advantage of clearing areas of the enemy without damaging the defensive positions. This meant an attacker had immediate cover, once having taken the enemy line.

Because these agents do not create damage, they therefore do not hinder the passage of tanks and troops.

On the defensive, Irritants could be used to fire on enemy batteries, causing them to have the same disadvantages. Even if firing fairly blind, a 'near enough' carried on the breeze could still force them to 'mask up'. They could be used to disrupt enemy communications, HQ and assembly areas, to disrupt the attack. The gasses could be fired close to one's own troops (who are already masked up), to prevent the enemy moving close without having to wear masks.

So, it can be seen that Irritants were extremely important, and were therefore used in vast amounts. It was not unusual for it to comprise 60% of the ammunition for a pre-attack bombardment. 33% was fairly normal. 25% would be considered the minimum requirement.


If the main advantage of Irritants was that they forced men to mask up or move away, the effect of being pounded with Mustard Gas was even more dramatic. Now they not only needed to mask up, but to wear protective clothing as well. Exposed areas of flesh had to be covered with a special cream.

So once again, it caused artillery to fire more slowly, or to move away entirely.

Everything about it caused difficulties. Men and animals picked it up on their feet and spread it. Despite precautions, the smallest drop could cause blisters and injuries - this increased casualty rates. The slightest drop in the eyes caused total blindness for periods of up to three months.

If it was breathed in, death would occur in a horrible manner. This resulted in a huge morale effect on those not killed, but who were worried as hell that it was going to happen to them next.

Because it gathers in low places, troops cannot use trenches and dugouts. Everyone has to get out of its way. If fired into towns, it can cause them to be abandoned for many hours. It hangs around, continuing to make the area unusable for 72 hours in the open, or up to 7 days in towns, ruins and woods.

It is therefore the perfect weapon to prevent the other side moving troops through an area. The zone needs to be marked out on the wargames table, as it was visible. If they choose to move through there, they take casualties the same as anyone else.

These chemicals do not distinguish between one side or the other, civilian or soldier. For this reason it was usually put down on the flank areas of an impending attack, to make it hard for reinforcements to be brought in from the flanks. As the attacker did not intend to pass through these flank areas, he was not worried about his own casualties.

For the above reasons, Persistents were always a fairly strong part of the ammunition percentage allocated.

Putting It Together in a Wargame Context

So, in a divisional or larger wargame, bombardments would be vital. Nobody attacked unless they had sufficient stores and ammunition built up. Pre-attack bombardments were therefore quite large. Defensive fire will be much less if the defender was not aware, or even partially aware, that he was to be the subject of an offensive.

The attacking player would need to plan a bombardment, as in real life. This is something like it would be in 1918:

  1. He would use HE and shrapnel to destroy wire.
  2. If British, he might plan a beam attack the night before the attack.
  3. HE, shrapnel and Irritants are put down on the enemy trenches to force them to mask up and inflict casualties on troops who left cover. It might also be mixed with smoke to cause confusion and reduce visibility.
  4. HE, shrapnel and Irritants on the enemy close defensive batteries forces them to mask-up and reduce their rate of fire and visibility….but also inflicts casualties. Again, smoke might be used to make up for a shortage of real gas, and confuse the target as to what it was.
  5. HE and Irritants are put on enemy machinegun positions. The HE might destroy them altogether. The Irritants will certainly reduce their effectiveness.
  6. HE, shrapnel and Irritants are used on enemy reserve areas to force them to mask-up,.and reduce their rate of fire, visibility, and slow their ability to move up.
  7. Persistents are used on the flanks outside the planned attack area, to prevent enemy reinforcements moving in from the flanks.
  8. Persistents are used on distant (heavy) batteries, where occupying or passing through the areas was not part of the immediate battle plan.
  9. Persistents are used on enemy reserve areas to force them to move away and prevent their intervention, as long as the areas are not part of the attacker's plans for passing through or occupation for 72 hours.
  10. Persistents used on on enemy senior HQ areas to force them to move, and therefore disrupt command and control. The attacker might mix this with shrapnel and HE to inflict casualties on them as they try to move, thereby causing even more disruption.
  11. Smoke and Irritants are lobbed into various other areas to create confusion as to the actual attack plan. (Do not use Persistents for this, as that would only signal that the attacker was not going through there.) If the attacker has guns and plenty of HE to spare, he might use some HE to perpetuate the confusion.
  12. For the attack, concentrate light and medium artillery (usually, the light) to form various types of attacking barrages. A box barrage enables troops to move inside it, and the enemy outside of the box to be unable to move in to intervene. This would be popular where there was no Persistents to protect the flanks. The barrage marches slowly forward at walking pace across the battlefield, with attacking troops as close behind it as they dare. This type of bombardment will make it hard to see the attackers, and hard for the defenders to do anything about them without risking heavy loss by exposing themselves.
  13. Medium guns will lift from the frontal areas, and commence to pound the rear areas with Irritants to prevent or slow the movement of reserves to counterattack. They will intensify their bombardment of the distant batteries with Irritants, HE and shrapnel as they try to intervene. Heavy guns will switch to crossroads with HE, Irritants and shrapnel, also to prevent reserves moving up.

The defender should plan certain areas to be pre-determined zones of fire. When the attack gets under way, these would be initiated through a series of flares, rockets, or other signals. They would probably include shrapnel and Irritants put down in no-man's land to hopefully catch the attackers in the open. They would dump as much Irritant as possible on enemy batteries - and probably include some Persistents, since they are not attacking. They would mix this with HE to kill, and also spread the Persistents.

If the defending batteries received the signal that the frontal areas had fallen, they might well have a planned bombardment with their whole arsenal of nasty stuff, to prevent the enemy using the area. (Of course, preventing the defender from doing this is the reason why the enemy pre-attack bombardments have been so well planned.)

Gas Masks. Note that even modern-day chemical warfare suits do not allow for the wearer to run or do anything too strenuous. The WWI sets were crude by comparison, hot and sweaty to wear, and often very uncomfortable. Some types were not all that effective at keeping gas out!

German flamethrower crews normally used gas masks when operating their weapons, due to the need to protect their flesh. They also wore heavy gloves. This is why some battle reports talk of the Germans 'walking' across no-man's land, squirting flame.

Having a serious Divisional-level WWI battle without chemical artillery playing a major role is totally unrealistic, both in method and historical fact.

Very few WWI wargames rules effectively cover the effects of gas weapons - probably because they are not understood. Gas is generally considered a horror weapon of WWI, and although tempted into the period, many rule writers seem reluctant to accept the need to reflect the historical realities.

As wargamers reflecting history, it is not our role to change that history to suit out abhorrence of these weapons. Nor is it really for us to judge those who used them. Not correctly reflecting the use of gas in WWI wargames would be akin to refusing to use arrows in an Ancients game because they put eyes out! History is history.

Select Bibliography

CHEMICAL SOLDIERS. British Gas Warfare in WWI. Donald Richter. Kansas Publishing.

GAS. The Battle for Ypres, 1915. J.M.Williams and R.J.Steel. Vanderwell publishing.


WITH A MACHINEGUN TO CAMBRAI. George Coppard. Imperial War Museum.

GAS ATTACK. William Moore. Leo Cooper Publishing.

TANK BATTLES OF WWI. Bryan Cooper. Ian Allen Publishing.



THE OFFICIAL HISTORY OF AUSTRALIA AT WAR 1914-18. C.E.W.BEAN. Australian War memorial.

THE 1917 SPRING OFFENSIVES. Yves Buffetaut. Historie & Collections.


WARRIOR NATION. John Thomson. Hazard Press.

GAS WARFARE IN WWI. A.J.Flintham. Educational Chemistry.

GASSED! Whyler. The infantry experience. Army Press.

GAS. Story of the special brigade. C.H.Foulkes. Edinburgh London Press.

THE POISONOUS CLOUD. Ludwig F. Haber. Oxford Press.

DEATHS MEN. D. Winter. London Press.