Direct proof of use
The U.S. Marine Corps' official VMFA-211 squadron history documents VMA-211 AV-8B Harriers operating from USS Makin Island and forward-deployed locations in combat operations against ISIL in Iraq and Syria from October 2014 to March 2015. The same history states that this final AV-8B combat deployment for VMA-211 included more than 650 combat missions, 4,500 combat hours, and more than 91,000 pounds of ordnance employed in support of Operation Inherent Resolve.
A Defense Visual Information Distribution Service image from January 17, 2015 separately identifies a VMA-211 AV-8B Harrier preparing for a flight in support of Operation Inherent Resolve in the U.S. Central Command area of responsibility. The caption describes the Harrier role set as coordinated strikes, close air support, and non-traditional intelligence, surveillance, and reconnaissance.
Sources: VMFA-211 Squadron History, DVIDS VMA-211 OIR Flight
Timeline
AV-8B use in the campaign began as a ship-based Marine expeditionary air component. Marine Corps Times reported that a 22nd Marine Expeditionary Unit Harrier from USS Bataan struck an Islamic State target near Haditha Dam in Iraq in September 2014, while other Harrier sorties from the Bataan Amphibious Ready Group provided armed non-traditional intelligence, surveillance, and reconnaissance.
VMA-211's main documented AV-8B deployment followed shortly afterward. Its detachment deployed aboard USS Makin Island in July 2014, the main element deployed in September 2014 with SPMAGTF-CC-CR 15.1, and VMA-211 Harriers then conducted Iraq and Syria combat operations from October 2014 until the squadron's March 2015 return.
Sources: Marine Corps Times Haditha Dam, Marine Corps Times 22nd MEU Strikes, VMFA-211 Squadron History
Operational role
Within the anti-ISIS coalition air campaign, the AV-8B functioned as a Marine expeditionary strike and fire-support aircraft rather than as a transferred partner system. Its documented missions combined armed reconnaissance, close air support, and strike sorties from amphibious shipping and forward-deployed positions.
RAND's study of the air war against the Islamic State places U.S. Marine Corps AV-8B Harriers among the aircraft used around Mosul alongside B-52 bombers, F-15E fighters, F-22 fighters, AH-64 Apaches, and ISR aircraft. That broader account frames coalition airpower as a primary U.S. and coalition contribution to the partner-led campaign against ISIS territorial control.
Sources: DVIDS VMA-211 OIR Flight, RAND Air War Against ISIS