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By Erik Ortiz

When ISIS began carving up parts of Iraq in June 2014, President Barack Obama sent the first flurry of U.S. troops to protect the U.S. embassy and other key assets.

That was just the beginning.

Since then, the overall number of U.S. troops there has grown in sporadic bursts — and it is set to climb to 5,262 after the Pentagon announced Wednesday it would dispatch an additional 615 to assist Iraqi government forces.

U.S. troops have been serving as mostly non-combat advisers and make up just a fraction of the 170,000 deployed during the height of the American occupation following the 2003 invasion.

Here's a brief chronology, according to some of the Pentagon's figures:

June 2014: 800 troops were added as part of the White House's plan to bolster Iraq's security in the face of insurgent attacks. In addition to the 275 first deployed, other forces began arriving in waves that month.

September 2014: 350 troops were added to further protect the U.S. embassy and surrounding facilities. The move came as Obama vowed he would "degrade and destroy" ISIS following the beheading of a second American journalist.

June 2015: 450 troops were added to help Iraq's military take back the city of Ramadi.

December 2015: 100 troops were added to help support the mission and assist the Iraqis on the front lines. At this point, U.S. military service members totaled about 3,500.

April 2016: 200 troops were added as part of a growing train-and-advise effort to help fight ISIS.

July/August 2016: 560 troops were added to deploy for infrastructure and logistical support at Qayara airfield south of Mosul, the second-largest city in Iraq and ISIS's last major stronghold. At this point, the troop level reached 4,647.

September 2016: 615 troops being added to help government forces finally oust ISIS from Mosul.

Courtney Kube contributed.