A contingent of artillery Marines recently arrived in Syria to support friendly forces isolating Raqqa, the de facto capital of the Islamic State, according to Marine Corps Times.

Though U.S. Central Command did not identify the unit now in Syria, Marine Corps Times’ Jeff Schogol noted that they seem likely to belong to the 24th Marine Expeditionary Unit, which is in the region on a scheduled deployment with USS Bataan’s amphibious ready group. On April 23, the 24th MEU posted a photo to the unit’s Facebook page, showing artillery Marines at Camp Buehring, Kuwait, firing M777 A2 howitzers at an artillery range.

If the recently arrived Marines are in fact from the 24th MEU, this marks the third time in just over a year that artillery Marines from a MEU have deployed to establish or man a semi-permanent fire base in support of ground operations against the Islamic State.

Related: Marine Expeditionary Unit Returns Home From Syria Deployment »

The first was in March 2016, when roughly 180 Marines from the 26th Marine Expeditionary Unit established Fire Base Bell, in Iraq, and fired more than 2,000 artillery rounds from their Howitzers over a two-and-a-half month stretch in support of Iraqi and Kurdish forces fighting ISIS in Mosul. The forward-positioned fire base came under frequent fire and on March 19, 2016, Staff Sgt. Louis Cardin was killed, and eight other Marines were wounded in an ISIS attack on the base. The artillery Marines were eventually replaced by an Army battery in 2016.

Then in March of this year, Marines from the 11th MEU arrived in Syria, where they pre-positioned howitzers to provide artillery support for friendly ground forces. Based on Marine Corps Times’ coverage, it appears the newly arrived Marines — ostensibly from the 24th MEU — have taken over that mission. News of the 11th MEU’s arrival in Syria came to light around the same time that Army Strykers belonging to the 75th Ranger Regiment were spotted in Northeast Syria, Task & Purpose’s Adam Linehan reported in March.

The 11th MEU is on its way home to San Diego, California, and is slated to arrive later this week.

A Marine expeditionary unit offers commanders and leaders flexibility in conducting humanitarian aid missions, and functions as a hard-hitting and highly versatile tool for waging war. When joined by an amphibious readiness group, a Marine expeditionary unit functions as a self-contained fighting force, able to put troops ashore, and provide them with air, fires and logistical support.