American troops are on the ground and fighting in Iraq. Two weeks after an American marine sergeant was killed (on March 19th) about 70 kilometers southeast of Mosul by an ISIL rocket the United States admitted that the dead marine and the other 200 marines he was with were doing a lot more than advising. These marines were providing artillery support for the Kurdish Iraqi forces and the incident took place within Kurdish controlled territory. Since the U.S. got involved in Iraq again after mid-2014 ten American military personnel have died there. But the U.S. now admits that it has nearly 4,000 troops in Iraq and a growing number of them are close enough to the fighting to be at risk. Except for a few American commandos, no U.S. troops are engaged in close combat. That is being left to the Iraqis. The Kurds are among the most effective troops Iraq has and the ones most qualified to carry out attacks. American troops have been training, advising and fighting alongside Kurds since the early 1990s.
When the U.S. marine was killed he was supporting one of those Kurdish attacks against ISIL (Islamic State in Iraq and the Levant) forces. The Kurds have been successful at this but like their American counterparts they prefer to keep their losses down. Having good artillery support helps with this. For political reasons (the Iraqis Arabs fear the Kurds) the Kurds have little in the way of artillery but they know how to work with American air support and American artillery support is not much different. The U.S. has long admitted that it prefers to deploy its ground controller teams (for calling in air strikes) with Kurds. The United States does not like to publicize this preference for the Kurds but it is an open secret in the American and Iraqi military.