A U.S. Air Force F-15E Strike Eagle flies over northern Iraq after conducting airstrikes in Syria. (Senior Airman Matthew Bruch/U.S. Air Force via AFP/Getty Images)

The United States has likely spent between $780 million and $930 million in its military campaign against the Islamic State militant group so far, and it will likely cost between $200 million and $320 million per month going forward if conducted with about 2,000 U.S. service members on the ground, according to a new report published Monday.

Those costs would grow to between $350 million and $570 million per month if the pace of the airstrikes increases and 5,000 U.S. troops are deployed, according to the report, released by the independent Center for Strategic and Budgetary Assessments in Washington. On an annual basis, lower-intensity air operations could cost $2.4 billion to $3.8 billion per year, the report said. The annual cost would jump to between $4.2 billion and $6.8 billion if the pace of airstrikes increases and is sustained.

The report was released after the United States reported completing about 220 airstrikes in Iraq since Aug. 8, and about 40 more in Syria since they began there early Sept. 23 On Monday, the U.S. military announced that along with partner nations, it had launched eight airstrikes in Syria. Separately, the United States carried out three airstrikes in Iraq.

In addition to the airstrikes, the U.S. Navy also has launched at least 47 Tomahawk cruise missiles, which each cost more than $1 million, into Syria. Most of those were aimed at targets affiliated with the Khorasan Group, which U.S. officials say is affiliated with al-Qaeda and which was was planning “imminent” attacks against the United States and other Western nations.

Airstrikes have been conducted thus far by fighter jets, “attack aircraft” like the AC-130 gunship, drones and the B-1B bomber. At this point, the Air Force, Navy and Marine Corps all have played a hand. There are believed to be more than 1,000 U.S. service members on the ground — many of them Special Operations troops — and the U.S. is preparing to deploy a 500-soldier headquarters to Iraq from the U.S. Army’s 1st Infantry Division, of Fort Riley, Kan.

CSBA released this graphic illustrating various costs associated with the fight:


This graphic, released by the independent Center for Strategic and Budgetary Assessments, illustrates various costs associated with the U.S. fight against the Islamic State militant group. (Graphic released by CSBA)

The United States is starting to see help it didn’t have previously in the fight against the Islamic State. Partner Arab nations have been carrying out airstrikes in Syria with U.S. oversight, and France, Britain and other nations have recently pledged support for the campaign in Iraq or have already joined it. Nevertheless, here are three scenarios laid out by CSBA analysts for the future:

A continue air campaign of similar scope: $200 million to $320 million per month
The United States was carrying out about 60 air sorties per day to conduct surveillance over Iraq before it expanded operations into Syria, meaning even more are likely needed now. As time progresses, it’s likely that the amount of airstrikes the U.S.-led coalition carries out will dwindle, but the aerial intelligence gathering will continue. There are currently about 1,600 U.S. service members deployed in Iraq as part of the mission, which will likely grow to about 2,000 personnel once the 1st Infantry Division headquarters arrives in Baghdad and Irbil, the city in Iraq’s Kurdish region where the United States has a large presence.

A larger air campaign: $350 million to $570 million per month
This assumes two things: the United States bumping up its campaign to about 120 surveillance flights and 150 airstrikes monthly, while expanding its presence on the ground to about 5,000 service members.

“Boots on the ground”: $1.1 billion to $1.8 billion per month
This scenario has been ruled out by President Obama. It assumes an even larger air campaign, with 150 surveillance flights and 200 targets hit monthly in Iraq and Syria. It also assumes 25,000 U.S. service members on the ground in Iraq and Syria, as some have advocated. About 80 percent of the cost with scenario would come from sustaining the ground forces.