Operation Inherent Resolve (OIR) is the United States military's operational name for the international war against the Islamic State (IS)—a group also known as the Islamic State of Iraq and Syria (ISIS), the Islamic State of Iraq and the Levant (ISIL) or its Arab acronym "Daesh"—including both a campaign in Iraq and a campaign in Syria, with a closely related campaign in Libya.
Through 18 September 2018, the U.S. Army's III Armored Corps was responsible for Combined Joint Task Force – Operation Inherent Resolve (CJTF—OIR) and were replaced by the XVIII Airborne Corps. The campaign was primarily waged by American and British forces in support of local allies, most prominently the Iraqi Security Forces (ISF) and Syrian Democratic Forces (SDF). Combat ground troops, mostly special forces, infantry, and artillery have also been deployed, especially in Iraq. Of the airstrikes, some 80% have been conducted by the military of the United States, with the rest by the United Kingdom (Operation Shader), Australia, Belgium, Canada, Denmark, France, Jordan, the Netherlands, Saudi Arabia, Turkey, and the United Arab Emirates.
By October 2017, around the time of IS's territorial defeat in Iraq, CJTF—OIR claimed that around 80,000 IS militants had been killed by it and its allies (excluding those targeted by Russian and Syrian air strikes). According to the Pentagon, by March 2019, the day of IS's territorial defeat in Syria, CJTF—OIR and its partner forces had liberated nearly 110,000 square kilometers (42,471 square miles) of land and 7.7 million people from IS, the vast majority of the self-proclaimed caliphate's territory and subjects. By the end of August 2019, it had conducted 34,573 strikes. Tens of thousands more were killed by partner forces on the ground (the SDF alone claimed to have killed 25,336 IS fighters by the end of 2017). According to Airwars, between 8,220 and 13,299 civilians were killed in the airstrikes in Syria and Iraq, with an additional 1,437 civilians killed in other operations.
Contents
Background
The United States relied on a combination of legal frameworks to justify its use of force against ISIS in Iraq and Syria, namely: military assistance on request, self-defence under Article 51 of the United Nations (UN) Charter, and the "unwilling or unable" doctrine. However, this legal reasoning was not unanimously accepted by other coalition members, resulting in differing geographic scopes of operation—some states restricted their involvement to Iraq, while others also conducted operations in Syria. Moreover, these justifications continue to be the subject of legal debate among scholars.
Legal basis under international law
International law prohibits the use of force against another state, as provided in Article 2(4) of the UN Charter. However, there are two exceptions to 'violate' this legal prohibition, which is through authorisation of the United Nations Security Council (UNSC), as stated in Article 42 of the UN Charter, and in self-defence, in accordance with Article 51 of the UN Charter.
Military assistance provided at the request of a state does not require UN authorisation nor the invocation of Article 51, as it falls within a state's sovereign right under customary international law to request such assistance and does not necessarily entail the use of force. As such, it does not constitute a 'violation' of the prohibition on the use of force. However, in order to remain within the legal framework of military assistance—rather than constituting an intervention that breaches the prohibition on the use of force—the inviting state determines the scale and scope of the intervening force, as the operation's sole purpose is to provide assistance to the inviting sovereignty. Furthermore, the inviting state cannot legally authorise the use of force on foreign territory, as this would violate Article 2(4) of the UN Charter, therefore, military assistance on request is confined to the borders of the inviting state.
In 2014, the Iraqi government submitted two formal letters to the UNSC, requesting military assistance in response to the ongoing threat posed by ISIS along its borders. Several states participating in OIR acted solely on the basis of this request, thereby limiting their operations to Iraqi territory, as the Iraqi government had no legal authority to authorise military action on Syrian soil. By responding exclusively to Iraq's request, the scale and scope of the foreign military presence was determined through agreements with the Iraqi authorities and remained confined within Iraq's borders, despite ISIS maintaining a stronghold in eastern Syria. The Obama administration relied on this legal framework—military assistance upon request—to justify its operations within Iraq. However, as Syrian President Bashar al-Assad had not granted consent for foreign military intervention, an alternative legal basis was required to justify military action against ISIS in Syria.
Additionally, scholars such as Ashley Deeks have argued that the U.S. tends to avoid relying on military assistance upon request as a legal framework, as such operations are entirely dependent on the level of consent granted by the inviting state and could require the U.S. to withdraw its forces should that state revoke its request.
History
2014
Unlike their coalition partners, and unlike previous combat operations, no name was initially given to the conflict against IS by the U.S. government. The decision to keep the conflict nameless drew considerable media criticism.
The U.S. decided in October 2014 to name its military efforts against IS as "Operation Inherent Resolve"; the U.S. Central Command (CENTCOM) news release announcing the name noted that:
According to CENTCOM officials, the name INHERENT RESOLVE is intended to reflect the unwavering resolve and deep commitment of the U.S. and partner nations in the region and around the globe to eliminate the terrorist group ISIL and the threat they pose to Iraq, the region and the wider international community. It also symbolizes the willingness and dedication of coalition members to work closely with our friends in the region and apply all available dimensions of national power necessary—diplomatic, informational, military, economic—to degrade and ultimately destroy ISIL.
The US Defense Department announced at the end of October 2014 that troops operating in support of Operation Inherent Resolve after 15 June were eligible for the Global War on Terrorism Expeditionary Medal.
By 4 December 2014, three U.S. service members had died from accidents or non-combat injuries.
2015
In November 2015, Commodore Captain Augustus Bennett commanding the USS Kearsarge (LHD-3) Amphibious Ready Group entered the 5th Fleet AOR in conjunction with the 26th Marine Expeditionary Unit under the command of Colonel Robert Fulford, consisting of the, USS Arlington (LPD-24) and USS Oak Hill (LSD-51) to commence airstrikes on IS. Prior to this, the ARG rendezvoused with the Turkish Navy for Egemen 2015. They concluded their OIR mission on 10 March with a total of 130 sorties and 60 strikes.
On 22 October 2015, a U.S. Master Sergeant, Joshua Wheeler, was killed in action when he, with about 30 other U.S. special operations soldiers and a Peshmerga unit, conducted a prison break near Hawija in the disputed territories of Northern Iraq, in which about 70 hostages were rescued, five IS members were captured and "a number" were killed or wounded. Sergeant First Class Thomas Payne was awarded the Medal of Honor for his actions during the operation. The Kurdistan Regional Government said after the raid that none of the 15 prisoners it was intended to rescue were found.
From May, North American Rockwell OV-10 Broncos joined the operation, flying more than 120 combat sorties over 82 days. It is speculated they provided close air support for special forces missions. The experiment ended satisfactorily, but a US Air Force spokesman stated it remains unlikely they will invest in reactivating the OV-10 on a regular basis because of the overhead cost of operating an additional aircraft type.
2016
By 9 March 2016, nearly 11,000 airstrikes had been launched on IS (and occasionally Al-Nusra), killing over 27,000 fighters and striking over 22,000 targets, including 139 tanks, 371 Humvees, and 1,216 pieces of oil infrastructure. Approximately 80% of these airstrikes have been conducted by American forces, with the remaining 20% being launched by other members of the coalition, such as the United Kingdom and Australia. A total of 7,268 strikes hit targets in Iraq, while 3,602 hit targets in Syria. On 12 June 2016, it was reported that 120 IS leaders, commanders, propagandists, recruiters and other high-value individuals were killed so far this year.
Until March 2016, U.S. military members were ineligible for Campaign Medals and other service decorations due to the continuing ambiguous nature of the continuing U.S. involvement in Iraq. However, on 30 March 2016, U.S. Secretary of Defense Ash Carter announced the creation of a new medal, named "Inherent Resolve Campaign Medal".
On 3 June 2016, aircraft flying from the USS Harry S. Truman in the Mediterranean Sea began airstrikes on IS. On 16 June 2016, AV-8B II+ Harriers of the 13th MEU flying from the USS Boxer in the Persian Gulf also began airstrikes on IS, marking the first time the U.S. Navy used ship-based aircraft from both the Mediterranean and the Persian Gulf at the same time during Operation Inherent Resolve.
By 27 July 2016, U.S. and coalition partners had conducted more than 14,000 airstrikes in Iraq and Syria: Nearly 11,000 of those strikes were from U.S. aircraft and the majority of the strikes (more than 9,000) were in Iraq. Of the 26,374 targets hit, nearly 8,000 were against IS fighting positions, while approximately 6,500 hit buildings; IS staging areas and oil infrastructure were each hit around 1,600 times. On 15 December 2016, the U.K. Defense Secretary Michael Fallon said that "more than 25,000 Daesh fighters have now been killed," a number that was half of the United States' estimate. When asked about this discrepancy, the UK's Ministry of Defense said that it stood by his estimate.
Since the first U.S. airstrikes on IS targets in Iraq on 8 August 2014, over two years, the U.S. military has spent over $8.4 billion fighting IS.
BBC News reported in 2017 that according to the American think tank Council on Foreign Relations, in 2016 alone, the U.S. dropped 12,192 bombs in Syria and 12,095 in Iraq.
2017
According to the Syrian Observatory for Human Rights, Coalition airstrikes have killed 7,043 people across Syria, of which: 5,768 dead were IS fighters, 304 Al-Nusra Front militants and other rebels, 90 government soldiers and 881 civilians. The air strikes occurred in the period between 22 September 2014 and 23 January 2017.
In March 2017, various media outlets reported that conventional forces from the 11th MEU, as well as special operations forces of the 75th Ranger Regiment deployed to Syria to support U.S.-backed forces in liberating Raqqa from IS occupation. The deployment marked an escalation in the U.S. intervention in Syria.
By 28 February, the Coalition had conducted 3,271 sorties in 2017, 2,129 of which resulted in at least one weapon released. In total, the coalition released 7,040 weapons in Iraq and Syria in this same time period in an effort to destroy IS.
As of 9 August 2017, coalition aircraft flew a total of 167,912 sorties, and conducted 13,331 strikes in Iraq and 11,235 strikes in Syria, for a total of 24,566 strikes.
2018
In February 2018, the 2nd Brigade Combat Team, 101st Airborne Division was awarded a campaign streamer following its deployment to Iraq. In May 2016, the brigade deployed to advise and assist, train and equip Iraqi security forces to fight the Islamic State of Iraq. The 2nd Brigade also conducted precision surface-to-surface fires and supported a multitude of intelligence and logistical operations for coalition and Iraqi forces. They also provided base security throughout more than twelve areas of operations. The Brigade also aided in the clearance of IS from Fallujah, the near elimination of suicide attacks in Baghdad, and the introduction of improved tactics that liberated more than 100 towns and villages. The 2nd Brigade, 101st Airborne Division also played a significant role in the liberation of Mosul.
2019
In early 2019, the US-led coalition focused on the final assault on ISIS in the Euphrates pocket, including the Battle of Baghuz Fawqani in the first quarter of the year. Civilian human shields held by ISIS were among the victims, including in one reported massacre on 19 March in which up to 300 civilians, including 45 children, were alleged to have been killed by Coalition forces.
From 8 August 2014, to 29 August 2019, coalition aircraft conducted a total of 34,573 strikes.
On 27 October 2019, the US conducted a military operation codenamed Operation Kayla Mueller, which resulted in the death of the ISIS leader, Abu Bakr al-Baghdadi in Idlib Governorate. It was reported that al-Baghdadi detonated a suicide vest, killing himself and two children after being chased into a tunnel.
On 31 December 2019, the CJTF-OIR reported its forces were "closely monitoring the current situation of the protests at the US Embassy in Baghdad", adding that they were "taking the appropriate force protection measures to ensure [US Embassy personnel] safety".
2020
CJTF-OIR paused all training and anti-ISIS operations on 5 January 2020, to focus on protecting Iraqi bases hosting Coalition troops in the wake of several rocket attacks. This action was also linked to the anticipated response against Coalition forces in the wake of the killing of Iranian General Qasem Soleimani. In March 2020, the U.S. military started to withdraw from various bases in Iraq.
2021
On 31 March 2021, Carrier Air Wing Three launched naval flight operations in support of Operation Inherent Resolve. The USS Dwight D. Eisenhower and its carrier strike group were expected to lead Task Force 50, which oversees Operation Inherent Resolve's naval strike operations.
2023
On 3 April, U.S. forces killed senior Islamic State leader Khalid 'Aydd Ahmad al-Jabouri, who was allegedly planning attacks in Europe during Easter, in an overnight drone strike on the outskirts of rebel-held town of Killi, Idlib in northwest Syria.
On 9 July, US Central Command announced that a U.S. MQ-9 drone which had been harassed by Russian aircraft for almost two hours had on 7 July killed an ISIS leader called Usamah al-Muhajir, who had been riding his motorcycle on the road linking al-Bab with Bizaah.
On 24 August, the U.S. Military stated that Major General Joel 'JB' Vowell had assumed command of anti-ISIS operation also known as Operation Inherent Resolve, from Major General Matthew McFarlane.
On 20 November, the United States Central Command has announced that, in the months of September and October, it has conducted, along with coalition and other partners, a total of 79 operations in Iraq and Syria resulting in 13 ISIS operatives killed and 78 detained.
2024
On 30 August, United States Central Command reported that "[U.S.] forces and Iraqi Security Forces conducted a partnered raid in Western Iraq in the early hours of Aug. 29, resulting in the death of 15 ISIS operatives." It was later confirmed that 7 U.S. troopers were injured during the operation.
On 31 December, French Defense Minister Sébastien Lecornu reported that French forces had carried "targeted strikes against Daech" targets "on Syrian soil", dropping seven bombs on two targets on 29 December. Multiple planes and a drone executed the strike off from Prince Hassan Air Base in Jordania.
2025
On 1 January 2025, an American man inspired by ISIS killed 15 people and injured 57 in a truck attack in New Orleans. On 9 January, the Islamic State, in the 477th issue of its weekly newsletter "Al-Naba", praised the attack and Jabbar himself, calling on other supporters to follow in his footsteps.
In April 2025, the U.S. ordered a consolidation of its forces in Syria under OIR, reducing troop numbers from about 2,000 to under 1,000 at selected bases, primarily in northeastern Syria.
On July 21, 2025, U.S. Army Maj. Gen. Kevin C. Leahy officially transferred command of CJTF-OIR to Brig. Gen. Kevin J. Lambert at Union III, Iraq.
Withdrawal of U.S. ground forces from Baghdad and key military bases in Iraq in August 2025.
2026
In February 2026, U.S. President Donald Trump ordered the complete withdrawal of American forces from Syria within the next two months. American forces completed their withdrawal on 16 April 2026, when US troops evacuated the Qasrak base in the Hasakah region, marking the end of more than a decade of American military presence in Syria.
In June 2026, U.S. CENTCOM conducted an airstrike in northwestern Syria killing Ali Husayn al-Ulaywi, who was the current leader of ISIS in Syria at the time. This marked the first known time, post U.S. withdrawal that the United States has conducted an attack in Syria and on ISIS.
With the withdrawal of U.S. Troops from Iraq 30 September 2026, CJTF-OIR and Operation Inherent Resolve mission set was moved to Jordan and CENTCOM quoted "Combined Joint Task Force-Operation Inherent Resolve (CJTF-OIR) remains operational and is now headquartered in Jordan as U.S. forces continue the counter-ISIS mission in Syria alongside Coalition partners and the Syrian government."
Assets
United States Air Force, United States Navy & United States Marine Corps units that are participating in this operations can be found in the aerial and ground order of battle.
United States Army
United States Navy
United States Air Force
United States Space Force
U.S. and coalition forces are training Iraqi forces at four sites: in al-Asad in Anbar province, Erbil in the north, and Taji and Besmayah in the Baghdad area.
Combined Joint Forces Land Component Command-Iraq
1st Infantry Division 1st Cavalry division
Division Headquarters and Headquarters Battalion
3rd Brigade Combat Team, 82nd Airborne Division (January – September 2015).
2nd Battalion, 505th Infantry Regiment
3rd Brigade Combat Team, 10th Mountain Division
1st Brigade Combat Team, 10th Mountain Division (September 2015 – June 2016).
2nd Brigade Combat Team, 101st Airborne Division (Air Assault) (June 2016 – January 2017).
1st Battalion, 502nd Infantry Regiment
2nd Brigade Combat Team, 82nd Airborne Division (January 2017 – October 2017)
Military bases
During the operation in Syria, there were several bases mostly in the north:
However, following the 2019 Turkish offensive into north-eastern Syria, most U.S. soldiers withdrew from northern Syria to western Iraq in October 2019, while even bombing their own Lafarge basement near Harab Isk.
Meanwhile, The New York Times reported that the Pentagon was planning to "leave 150 Special Operations forces at a base called al-Tanf". In addition, 200 U.S. soldiers would remain in eastern Syria near the oil fields, to prevent the Islamic State, Syrian government and Russian forces from advancing in the region. However, at least 600–900 U.S. Troops are expected to stay in Syria, in Al-Hasakah and Deir ez-Zor Governorates. In July 2020, the U.S. military built a new base including an airport, located between Um Kahif village and Tal Alu silos near Al-Yaarubiyah.
On 19 December 2024 the US government released a statement regarding the true size of the US presence to be 2000 troops.
Casualties
Combatants
American military casualties in Inherent Resolve totaled 118 dead (23 due to hostile action) and 496 wounded.
American and allied airstrikes killed tens of thousands of ISIL fighters in Iraq and Syria. The Syrian Observatory for Human Rights estimated a minimum of 9,200 ISIL fighters killed by airstrikes in the smaller Syrian theater alone by 2019, while noting that "the real number of casualties among ISIS and other Islamic factions is greater than what the Observatory has been able to document, given the intense secrecy of the targeted parties for their human losses." The American military gave its own data on the number of ISIS fighters killed in its strikes over time:
March 2015: 8,500+ killed per Lloyd Austin
September 2015: 20,000 killed per General Sean MacFarland
February 2016: 27,000 killed per an unnamed U.S. official
August 2016: 45,000 killed per General Sean MacFarland
December 2016: 50,000 killed per an unnamed U.S. official
February 2017: 60,000 killed per General Raymond Thomas
July 2017: 70,000 killed per General Raymond Thomas
October 2017: 80,000 killed per CENTCOM
These figures are do not take into account casualties inflicted by partnered ground forces with U.S. support.
Civilians
According to Airwars, in 2014 there were 63 incidents involving the US-led coalition in Iraq and Syria in which there were civilian casualties, causing at least 160 civilian deaths. In 2015, there were 268 incidents and 708 deaths. In 2016, there were 483 incidents and 1,372 deaths. Civilian casualties peaked in 2017, with 1,841 incidents and at least 4,677 civilian deaths.
According to Airwars, 1,472 civilians were killed by the U.S. air campaign in Iraq and Syria in March 2017 alone. On 17 March, a U.S.-led coalition airstrike in Mosul killed more than 200 civilians. Data compiled by Airwars shows that 229 strikes in Iraq and 878 strikes in Syria were carried out by Coalition forces in June 2017, killing an alleged total of 1,483 people. The reporting of 875 of those total alleged deaths is contested. In July 2017, Airwars recorded reports of an alleged 1,342 people were killed in Iraq and Syria by Coalition airstrikes. Of the allegations 812 were contested, and two were disproved.
Casualty figures fell after the 2017 peak. According to Airwars, 2018 saw 192 incidents and 846 deaths; 2019 saw 72 incidents and 467 deaths. In 2019, the casualties were concentrated in the first quarter during the Battle of Baghuz Fawqani including an alleged massacre of civilian human shields on 19 March.
By 2020, Airwars had recorded a five-year total of 14,771 US-led Coalition strikes in Iraq and 19,829 in Syria and investigated 2,921 alleged civilian casualty incidents, estimating 8,259–13,135 civilian deaths, of whom around 2,000 were children, although the Coalition itself estimated just 1,377 or 1,417 civilian deaths.
The New York Times reported that efforts to minimize and count civilian deaths fell far short of the approach promised by the US military for its use of airstrikes in the war against IS. The newspaper reported that airstrikes against IS, as well as in the war in Afghanistan, was marked by "flawed intelligence, poor targeting and thousands of civilian deaths." It also reported that efforts to minimize civilian casualties diminished after President Trump assumed office in 2017, stating "... the authority to approve strikes was pushed further down the chain of command, even as an overwhelming majority of strikes were carried out in the heat of war, and not planned far in advance." Finally, the paper reported that the US military systematically under-reported casualties, providing a total death count of 1,417, when the actual count was significantly higher. The report states that the military made little effort to accurately determine civilian casualties after the airstrikes. The military was also reluctant to divulge information about the casualties, in spite of promises of transparency, and news media were required to make numerous requests under the Freedom of Information Act, and had to repeatedly sue the US military to produce data.