From mid-2014, Islamic State (IS) began to use chemical weapons (CW) on the battlefields of Syria and Iraq. Since then, it has striven to develop more lethal CW, and formulate the necessary tactics to use them effectively. Through its territorial conquests in Syria and Iraq, it has gained access to a range of industrial chemicals including chlorine, phosphine and vinyltrichlorosilane, which it has used as CW. In addition, the chemicals that it now has access to, have enabled it to develop mustard gas. It has reportedly also succeeded in engineering CW warheads for a range of different delivery systems, including mortar rounds, heavy artillery shells, grad rockets, improvised rockets and mortars, vehicle borne IEDs (VBIED), and IEDs, which has given it a degree of tactical flexibility in the way that it uses CW.

Whilst IS’s use of CW has caused considerable concern, significant question marks remain over just how effective these attacks have actually been. To answer that question it is first necessary to understand exactly what IS has tried to use CW for. There have been several dozen reports of IS using CW, not all of which have been verified. Details of many of these incidents are also sketchy, but assuming that the available reports are true, IS’s use of CW can be broken down into four broad categories, which are described below.

Offensive military operations

During its offensive military operations, IS has used CW for both discriminate attacks against military targets and indiscriminate attacks on population centres. From the outset, it has primarily focused on using CW in its most important battles, particularly those where its initial conventional attacks had ground to a halt. This suggests that IS itself, believes that CW have the potential to play a decisive role on the battlefield.

There have been a number of reported instances of IS using CW against military targets. IS is believed to have first used CW in July 2014, during a battle to capture the village of Avdiko, in north east Syria. Very few details are available, but three Kurdish YPG fighters were reported to have been killed by the CW. This attack was part of a broader assault on the village, and whilst it contributed to the IS victory, it was unlikely to have been a decisive factor in the battle given the small number of casualties it caused. Later that year, IS conducted a number of small scale CW attacks during the battle for Kobane, in northern Syria. In the first instance, it is reported that a single CW shell or rocket injured 8 civilians. On another occasion in late October, IS forces used CW during an attack on the eastern side of the town. However, this use of CW had no impact on the overall course of the battle, which became IS’s first significant military defeat.[i]

Reports of IS’s use of CW in Iraq during 2014, are more mixed. As part of its offensive towards Baghdad, IS deployed chlorine IEDs during a successful assault on the town of Dhuluiya. The mainstream media reported a handful of Iraqi army and militia fighters being injured, although some social media reports reported higher numbers of casualties.[ii] The initial assault on Dhuluiya was successful, and the deployment of CW played a small role in that success. However, the battle continued for several months afterwards, until Iraqi security forces succeeded in liberating the town at the end of December 2014. There were no further reports of chlorine being used in Dhuluiya, but that may have been because 14 members of the IS CW unit at Dhuluiya were killed, and a further seven injured, in an explosion as they were filling rocket warheads with chlorine.[iii] In contrast, at the town of Saqlawiya near Falluja, IS used CW to supplement its conventional attacks on an Iraqi army regiment that had been surrounded. The Iraqi army eventually managed to re-open the road to Saqlawiya, but instead of trying to hold its positions in the town, it withdrew from them completely.[iv]

One of IS’s most significant and sustained uses of CW in offensive operations was on the Makhmour front, located south of Irbil and Mosul in northern Iraq. Beginning in August 2015, IS conducted a total of four CW attacks on the front, using chlorine and mustard gas in mortar rounds, improvised mortars, and Grad rockets. The largest of these bombardments comprised a barrage of 45 mortar rounds filled with mustard gas. Yet despite the larger quantities of CW used, only between 12 and 35 Kurdish Peshmerga fighters were reported to have been injured. Significantly, there are no reports of these CW bombardments being co-ordinated with IS infantry assaults on Peshmerga positions, and no reports that they led to IS being able to advance.[v] However, there is evidence of CW having a psychological impact on Peshmerga forces, with one fighter quoted as saying, “With the chemical attack, it isn’t clear what is going to happen, what the harm will be. For me, it is more dangerous than a normal attack.”[vi]

Examples of IS using CW indiscriminately during its offensive operations include the assaults on the town of Mare and Hassaka city in 2015, both of which are in northern Syria. During the battle for Mare, IS reportedly fired between 15 and 30 CW mortar or heavy artillery shells into the town, injuring 50 civilians.[vii] During the battle for Hassaka, IS fired more than 20 CW shells into civilian areas of the city, injuring several dozen civilians. This indiscriminate bombardment was combined with a targeted CW bombardment of YPG positions at Tel Brak, just outside the city, which injured 12 YPG fighters.[viii] In both instances, these barrages had no impact on the course of the battles.

For IS, the challenge has been to co-ordinate CW barrages with its infantry attacks. However, the available evidence indicates that IS has not even tried to co-ordinate the majority of its CW attacks with infantry assaults. This raises question marks about whether IS forces have the capability to operate in a chemical environment. If they don’t, it would significantly limit the effectiveness of using CW for offensive battlefield operations.

IS appeared to be trying to resolve these issues during a major assault on Deir-e-Zor airbase in north east Syria, in April 2016. The focal point of the assault was a number of regime-held villages just outside the airbase, which IS attacked with conventional SVBIED and a sustained infantry assault. At the same time, it shelled the airbase itself with mustard gas, injuring a number of Syrian army troops.[ix] The fact that IS was shelling areas inside the airbase when the main battle was taking place outside of the airbase, suggests that it may have been trying to use the CW barrage to tie down regime troops inside the airbase, to prevent them from reinforcing the battlefront. But again, there is no evidence that the use of CW had any impact on the course of the battle, because after initially making ground, IS forces were forced to retreat back to their starting positions.

Harassment of enemy forces

On a small number of occasions, IS has deployed CW as part of its on-going operations to harass enemy forces. For example, when the Peshmerga captured the Iraqi town of Sinjar in February 2016, they cut a vital supply line between the IS-held cities of Mosul in Iraq and Raqqa in Syria. IS did not attempt to re-take the town, but instead subjected the defenders to a sustained campaign of small scale shelling, skirmishing and sniping. As part of that campaign, it fired 19 improvised rockets with warheads containing Vinyltrichlorosilane into Peshmerga front-line positions. Over 100 people, mostly Peshmerga, were reported injured. Other reports speak of 30 mortar shells, injuring 30 people. Two days later, another barrage of CW mortar rounds hit Peshmerga positions in villages near the town, injuring 175 fighters, but killing none.[x]

The most significant feature of the second barrage, was an eyewitness report that the CW rounds landed in a field 200 meters behind the Peshmerga positions. At the time, the wind was blowing parallel to the front line, which resulted in most of the gas being blown away from the Peshmerga positions. This failure to take account of the prevailing weather conditions suggests that the unit using the CW may not have received adequate training in their operational use, and raises question marks about whether there have been other instances where the effectiveness of IS’s CW attacks has been limited by their poor operational use.

It is unclear what IS was trying to achieve with these particular CW attacks, but one potential explanation is that it was part of a longer term strategy to undermine Peshmerga morale at those locations, and force them to withdraw from their positions. But in the absence of any significant offensive action to seize the Peshmerga positions, these attacks achieved nothing.

Defensive military operations

By the time that IS was experimenting with its offensive CW tactics at Deir-e-Zor, it was being pushed back on several fronts in Iraq and Syria. As a consequence, it has also been forced to deploy CW extensively in defensive roles, to either try to blunt enemy attacks, or cover the retreat of its own forces following defeat on the battlefield.

One of the main ways it has used CW to cover a retreat and slow an enemy advance, is to use roadside CW IEDs. However, it has only deployed CW IEDs in limited numbers at any given location, usually only single IEDs. It is standard practice for IS forces to deploy multiple IEDs in areas from which it has retreated, forcing Syrian regime and Iraqi government forces to sweep for IEDs whenever they capture IS positions. So whilst IEDs may not kill or injure many troops, they can be effective in slowing any pursuit.

IS has also used CW in operations to try and blunt enemy attacks at a number of locations, particularly in defence of the city of Mosul during 2015 and 2016. In January 2015, IS deployed chemicals in a suicide VBIED against Peshmerga forces who were advancing to cut the Mosul to Syria road,, but the Peshmerga destroyed it with small arms fire.[xi] Conventional SVBIED have proven to be highly effective on numerous occasions in both Syria and Iraq, but there are no reports of a successful CW VBIED, and no evidence that CW VBIED are any more effective than conventional SVBIED.

During March and April 2016, IS reportedly used CW rockets at least 10 times in and around the town of Gwer, to fend off Peshmerga attacks. Only small numbers of Peshmerga are reported to have been injured by the CW, and it did not have any reported impact on the outcome of the fighting. However, there is further evidence of CW having a psychological impact on the Peshmerga forces. Colonel Srud al-Bazanji, the Peshmerga Chief of Staff for the area admitted that, “Normal weapons are better at causing death and injury but if you think chemical weapons are being used you are more afraid.”[xii]

Terror attacks against civilian targets

Whilst IS has primarily used CW in military roles, it has occasionally used them to terrorize the civilians, as an end in itself. This was particularly apparent at Taza, a Shiite Turkmen village 20km south of the city of Kirkuk in Iraq. IS had already been shelling the village for a sustained period of time before it launched two CW barrages on the village in March 2016. The first barrage, comprising 24 mortar shells and Katyusha rockets, injured more than 40 people. Three days later, the second barrage, comprising 45 rockets, reportedly killed a child and injured between 400 and 600 other people. Some reports speak of 25,000 people fleeing their homes as a result of these attacks.[xiii]

Eyewitness evidence from Taza and Sinjar has confirmed the terror effect of using CW on civilians. At Taza, a civilian reported that “there is fear and panic among the women and children … they’re calling for the central government to save them”. At Sinjar, another civilian reported, that “this is why we cannot come back …ISIS is still close enough to kill us in many ways. And now they are using chemical weapons. Please help us push them back far away, please stop them.” The apparent reason why CW have had more of a terror effect on civilians than conventional weapons is that people feel that they can hide from bombs and bullets but that they cannot hide from gas.[xiv]

It is not apparent why IS has used CW in this role given that its primary focus has been on using them to support its military operations. However, local officials have speculated that IS was deliberately trying to force the civilian populations of these towns and cities to flee their homes. This would have the dual effect of undermining civilian confidence in the Iraqi government and increasing the burden posed by internally displaced people.

Limited weapons, limited strategy

IS has tended to use CW tactically, in limited roles. Kurdish Peshmerga forces report having captured IS gas masks,[xv] but IS forces seem reluctant to operate in a chemical environment. When it has used CW to bombard enemy positions, it seems to have been in the hope that the bombardment itself would be sufficient to force enemy forces to withdraw from their positions.

Its decision to use CW in these limited roles seems to a large extent, to have been determined by the limited quantities of CW available to it, and the poor quality of its munitions. Large quantities of CW agent are required to have a decisive impact on the battlefield, and it is apparent from the relatively limited quantities that IS has deployed to date, that it does not have the required quantities. Given that, it is perhaps surprising that it has not reserved the limited quantities that it does have, for use in a smaller number of really critical battles.

Reports also suggest that despite IS making significant technological advances in developing new chemical agents and weaponising those agents, its CW remain relatively crude. In particular, the sulphur mustard agent that it has produced is of poor quality.[xvi] And whilst the industrial chemicals it has at its disposal can be lethal, they are nowhere near as lethal as nerve agents. There are also question marks over the accuracy of some IS CW munitions, and it is apparent that IS has not developed the technology to airburst its CW, because eyewitness evidence from Hassaka, Makhmour and Sinjar, indicates that the CW munitions exploded on impact with the ground. When CW warheads explode on impact with the ground, at least some of the chemical agent is consumed in the blast, thereby reducing its effectiveness.[xvii]

The variable quality of IS CW munitions was apparent from an attack at Keske junction, just outside Mosul. The junction is a strategic location, controlling the main supply route between IS-controlled Mosul and the Syria border. After it was seized by Peshmerga forces in January 2015, IS made repeated counter attacks in an effort to re-take the junction, but failed. In March 2015, it resorted to firing 20 CW rockets at the junction, but not only did they miss the Peshmerga positions, landing on civilian houses and fields, only one of the rockets actually exploded.[xviii]

Success or failure?

Whilst IS’s use of CW has clearly not had a decisive impact on the outcome of a single battle in Syria or Iraq, it should be observed that IS has not actually deployed CW in roles which would enable them to have a decisive impact on any individual battle. Instead, the effectiveness of IS’s use of CW needs to be considered in the context of the limited roles in which it has deployed them.

In these more limited roles, IS’s use of CW has, on occasion, been effective. In offensive military operations, they have been effective in killing and incapacitating small numbers of Peshmerga forces, and on occasion injuring hundreds of civilians. Whilst they cannot be said to have been the decisive factor in any single battle, they did contribute, even if only in a small way, to some IS victories. In defensive roles, CW IED may have been successful in slowing the advance of Peshmerga forces, and covering the retreat of IS forces, from a number of battles. Although they were probably no more effective in this role than conventional IEDs. The strongest evidence of their effectiveness comes from reports of their psychological impact on civilians at Sinjar and Taza. If displacing civilians was one of the main objectives for IS to use CW, then there is strong evidence of their effectiveness in achieving that.

There is also evidence from Gwer and Tal Brek of CW having a psychological impact on Peshmerga forces, but only limited evidence of this having any direct impact on Peshmerga operations. At Tel Brek for instance, the Peshmerga downgraded the position that had been attacked with CW from being a squad-sized outpost to being an observation post held by fewer fighters. Significantly however, there have been no reports of Peshmerga forces ever having retreated from their positions, or having cancelled any attacks on IS positions, in the face of CW attacks.

At Saqlawiya by contrast, a senior Iraqi general suggested that the use of CW was one of the reasons behind the loss of the town to IS.[xix] However, the Iraqi army’s withdrawal from Saqlawiya, was part of a much wider collapse during 2014. If CW were indeed a major reason for the loss of Saqlawiya, it may well have been because of low morale amongst the Iraq troops stationed there. This is supported by the fact that when IS used CW against Iraq government troops who were attacking Tikrit and Ramadi, between April and August 2015, they had no impact.[xx]

The available evidence suggests that IS CW have the potential to have a more significant impact on the battlefield, but that IS has not yet been able to exploit that potential. If IS can improve the quality of its CW, acquire greater quantities, and master the environmental factors associated with their use, they could prove to have a much greater impact than hitherto. But for IS to really take advantage of the casualties caused by CW, it also needs to develop more effective tactics for integrating them into its offensive operations. To date however, it has displayed only limited capacity to learn from its previous use of CW and adapt its tactics.

Notes and references

[i] Has ISIS Used Chemical Weapons On Kobane? Claims Under-Siege Town Was Hit By Crude Rocket Attack, Daily Mail, 24 October 2015,; Kurds Fear Isis Use Of Chemical Weapon In Kobani, The Guardian, 24 October 2014 ,; Gruesome Photos May Show ISIS Using Chemical Weapons On Kurds, Report Says,, 13 October 2014,; URGENT – PHOTOS: ISIS Uses Chemical Weapons Against Kurds In Kobanî, Again,, 22 October 2014,

[ii] Fourteen ISIS Fighters Killed Filling A Chemical Warhead, The Gateway Pundit 18 September 2014,; ISIS Gangs Used Chlorine Gas Against Iraqi Army,, 27 October 2014,; ISIS Chlorine Attack On Security Forces Confirmed – Iraq Officials, Russia Today, 24 October 2014,; U.S. Investigating Reports That ISIS Used Chemical Weapons,, 24 October 2014,; Iraqi Isis Militants ‘Use Chlorine Gas’ Against Security Forces, International Business Times, 24 October 2014,; Report: ISIS Steps Up Use Of Chemicals On Battlefields In Iraq And Syria, CNN, 20 July 2015,; Islamic State Used Chemical Weapons Against Peshmerga, Kurds Say, The Guardian, 14 March 2015,

[iii] Fourteen ISIS Fighters Killed Filling A Chemical Warhead, The Gateway Pundit 18 September 2014,; Twitter, A Stephen ‏@thykingdom2020, 22 September 2014.

[iv] Does ISIS Have Access To Chemical Weapons In Iraq And Syria?, NBC News, 28 October 2014,

[v] Eyewitness Account: ISIL Steps Up Chemical Weapons Attacks On Kurds In Iraq, USA Today, 10 March 2016,; IS ‘Used Mustard Gas’ Against Kurdish Forces, again, i24 nws,; ISIS Suspected Of Using Deadly Mustard Gas In Attack On Kurdish Town In Iraq Injuring 60 Fighters, Daily Mail, 14 August 2015,; Tests Prove ISIS Using Mustard Gas Against Kurds, Rudaw,; ISIS Attacked Kurds With ‘A Class One Chemical Agent.’ US Official Says, Rudaw,

[vi] Eyewitness Account: ISIL Steps Up Chemical Weapons Attacks On Kurds In Iraq, USA Today, 10 March 2016,

[vii] ISIS ‘Chemical Weapons Attack’ Victims Treated, Chanel 4 News, 25 August 2015,; Mustard Gas ‘Likely Used’ In Suspected Islamic State Attack in Syria, The Guardian, 26 August 2015,

[viii]  Islamic State Used Poison Gas In Northeast Syria: Kurds, Monitor, Reuters, 17  July 2015,; Islamic State Targets Civilians With Chemical Weapon Attack In Iraq And Syria, Islam Media Analysis, 20 luglio 2015,; ISIS Has Fired Chemical Mortar Shells, Evidence Indicates, New York Times, 17 July 2015,; ISIS Militants Launch Chemical Attack On Kurdish Areas Northeast Syria, ARA News, 22 May 2016,

[ix] ISIS Chemical Weapons Attack On Syrian Air Field, Rudaw, 5 April 2016,;; Terrified Families Flee Their Homes As ISIS Attack Their City In Iraq, Daily Mail, 5 April 2016,; Isis Chemical Weapons: Militants Use ‘Mustard Gas’ Against Syrian Forces In Battle For Deir ez-Zor Airport, Daily Mail, 5 April 2016,

[x] Eyewitness Describes Islamic State Chemical Attack On Kurdish Peshmerga,, 13 February 2016,; EXCLUSIVE: Daesh Used Corrosive Chemicals Against Iraqi Civilians, Sputnik News, 25 February 2016,; CBN On The Frontlines: ISIS Launches Gas Attack In Iraq, CBN News, 26 february 2016,; Daesh Used Chemical Arms Against Kurds In Iraq: Sources, press TV, 18 February 2016,; Attacks On Sinjar Highlight Dangers Posed By Group’s Homemade Gas-Filled Weapons With Kurdish Fighters Ill-Equipped To Protect Themselves, Middle east Eye, 6 March 2016,; IS  attacks Sinjar With Chlorine Chemical Weapons, Kurdistan 24, 26 February 2016,

[xi] Iraq’s Kurds Claim Isis Used Chemical Weapons In Attack On Their Fighters, The Independent, 15 March 2015,; Islamic State Used Chemical Weapons Against Peshmerga, Kurds Say, The Guardian, 14 March 2015,; More Evidence Emerges Of ISIS Using Chemical Weapons As Kurdish Fighters Seize Chlorine Canisters After Suicide Bomb Attack That Left Them ‘Dizzy, Nauseous And Weak’, Daily Mail, 14 March 2015,

[xii] Islamic State Using Chemical Weapons in Iraq, Kurds Say, By Ed Adamczyk, 22 April 2016,

[xiii] Iraq: Islamic State Chemical Attacks Wound 600, Kill 3-Year-Old Girl, World Bulletin, 14 Mar 2016,; Islamic State Militants Use ‘Poisonous Substances’ In Village Shelling; US Strikes Chemical Weapons Sites, ABC News, 9 March 2016,; Islamic State Chemical Weapons Attack Said To Injure 600 And Kill 3-Year-Old Girl In Iraq, Vice News, 12 March 2016,; Iraq Confirms Islamic State Use Of Chemical Weapons, Christian Science Monitor, 12 March 2016,; It’s Official: ISIS Is Using Chemical Weapons, Breaking Israel News, 13 March 2016,; Over 400 Injuries Reported In ISIS-Led Chemical Attack In Iraq’s Kirkuk, ARA News, 12 March 2016,

[xiv] Does ISIS Have Access To Chemical Weapons In Iraq And Syria?, NBC News, 28 October 2014,

[xv] Islamic State Used Poison Gas In Northeast Syria: Kurds, Monitor, Reuters, 17 July 2015,

[xvi] It’s Official: ISIS Is Using Chemical Weapons, 13 March 2016,

[xvii] ‘Threat Warning: JAM Claims Chem Rkts IVO Sadr City (LTIOV: 12 AUG 06) 2006-08-09 15:54:00’, Iraq War Logs, Wikileaks, <>.

[xviii] Eyewitness Account: ISIL Steps Up Chemical Weapons Attacks On Kurds In Iraq, USA Today, 10 March 2016,

[xix] Does ISIS Have Access To Chemical Weapons In Iraq And Syria?, NBC News, 28 October 2014,

[xx] ISIL Used Chemical Arms Against Iraq Forces In Tikrit, Press TV, 5 April 2015,; Iraqi Army Thwarts Chlorine Gas Attack by ISIL, FARS News, 6 April 2016,

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