British troops suffering the appalling effects of a German gas attack in 1918.
But now The Mail on Sunday has uncovered the first shocking evidence that Islamic State is using mustard gas on the front line in Iraq.
Troops fighting against the terror group have been left with appalling injuries - including agonising blisters on their skin and badly damaged lungs - in a frightening echo of warfare in the trenches on the Western Front.
The terror group - which has killed hundreds of victims in repeated attacks in France and against other targets in the West - is fighting a last-ditch battle to hold on to the dwindling area it controls in Iraq and Syria.
Nearly 100 Kurdish soldiers have been injured in mustard gas attacks, which are now taking place as often as twice a week, according to doctors speaking publicly for the first time.
The Mail on Sunday has interviewed victims of the weapons, which are banned by the United Nations.
They described poisonous yellow clouds of mustard gas burning their skin and damaging their lungs.
Their injuries have been verified as the effect of mustard gas, according to experts from the US and Italy.
They are convinced the jihadis are now producing sophisticated chemical weapons on an industrial scale in Iraq and fear IS will use them in a desperate bid to defend its stronghold city of Mosul in northern Iraq, which is now surrounded by UK-backed Iraqi and Kurdish troops.
Proof of IS's use of mustard gas comes just days after reports that President Assad's regime in Syria has been using chlorine gas against civilians.
Comment: They just had to throw that in there based on no evidence.
One Kurdish soldier spoke of how six Islamic State rockets containing mustard gas landed in the village of Sultan Abdullah in Gwer province, Iraq, while he was on patrol.
Father of six Mirmaj Hassan, 39, breathed in the noxious fumes, which also seeped inside his military uniform, causing large blisters on his skin.
The soldier, who was one of 13 Peshmerga victims of chemical weapons on August 12 last year, said: 'It was 6pm and the sun was going down. We'd been on the front line all day and everyone was exhausted.
Kurdish fighter Mirmaj Hassan and the blisters on his abdomen.
'I didn't have a gas mask so I covered my mouth with my hand.
'But I soon felt pain in my throat and my chest tightening. I collapsed on to the ground, sweating and completely out of breath.
'I tried to shout for help but could only gasp. Then I began to feel this strange burning sensation around my stomach and back.'
Hassan told The Mail on Sunday how he undid his belt and pulled up his green shirt to inspect the wounds. He said: 'My skin was going moist and turning to liquid, like I was holding a match to my abdomen. I touched it and it was very painful.
'Eventually some other Peshmerga saw me. They ran to where I had collapsed, picked me up and carried me into a hut.
'There was no medicine to give us. All the officers did was throw water over us. But the burning sensation continued and blisters appeared. I could hardly breathe. Even today I have a constant cough and feel like I'm choking.
'I spent four days in hospital before going back to the front line, because even the wounded have to fight Islamic State - we must get rid of them. We would be thankful for more protection - we need more gas masks and hoods. I still don't have either.'
To prove that the Peshmerga were victims of chemical weapons, doctors took blood and urine samples from injured troops.
Blistering on Kurdish victims' arm, left and right.
The results were verified by the Organisation for the Prohibition of Chemical Weapons (OPCW). The use of any mustard agents on the battlefield is banned under the 1993 Chemical Weapons Convention.
The head of the OPCW also said recently that there are 'extremely worrying signs' that Islamic State is making its own chemical weapons.
The CIA has also publicly confirmed that it believes IS has the ability to produce mustard gas and chlorine.
The tests were ordered by the Peshmerga's head of medical affairs, Dr Muhsin Zangana, who said: 'There can no longer be any doubt that Islamic State is using chemical weapons against us, weapons which are getting bigger every week and can be fired from a longer range so they are more difficult to detect.
'I personally have treated victims from more than 50 attacks and the symptoms are consistent - the burns, ulcers inside the body, damage to the lungs, dry eyes and rashes.
'We are fortunate that no soldiers have died yet but we have one victim from Gwer last year who is getting worse. He could die if he is not flown overseas for treatment. We don't have what he needs.'
Dr Jodal Ahmed. a civilian doctor from Erbil in Iraq, has also treated chemical weapons victims, even though he has received no specific training. Dr Ahmed also said there was a shortage of medicines for the troops affected by the gas.
He said: 'They're given Salbutamol tablets [a drug also used to treat asthma] to help them breathe and eye drops. It's not enough. And I am seeing more and more cases like this. The Peshmerga deserve better treatment.'
Blistering on Kurdish victims' arm, left and right.
He said: 'Germany and the United States have given us 15,000 masks but we need 50,000, as the jihadis will use chemical weapons when we advance on Mosul. Last year their chemical weapons were 60mm short range shells which didn't include much gas.
'Now they're using 1m-long Grad rockets, with a lot more of the harmful substances in the nose of the missile.
'Most of the chemical weapons attacks on us happen near Mosul. This points to the gas bombs being produced there. Intelligence reports also say the chemistry department at Mosul University is being used to make chemical weapons.
'They are concocting a new generation of explosive devices and I believe Daesh [IS] will soon be able to inflict mass casualties. We will be unprepared and ill-equipped.'
Even Kurdish officers must go without gas masks on the front line.
One, Major Farhad Merozi, explained that when a rocket containing mustard gas exploded just yards from him on May 14 this year in Gwer, all he could do was wrap a wet towel around his head.
Within seconds he was vomiting and he temporarily lost his sight. He then fell unconscious.
Eventually he was taken to hospital and given oxygen.
He said: 'It was a very frightening experience, I couldn't understand what was happening to my body.
'We'd been firing rocket-propelled grenades at Daesh when suddenly they responded with rocket fire.
'Seventeen of us were injured, all with burning skin and gasping for breath. It was horrible. I will never forget it.
'Three months later I have terrible chest pains and haven't gone back to the front line.'
Comment: Mustard gas also used in Syria: Aleppo forensics reveal terrorists using mustard gas