Go Kurds. They are like the Northern Alliance was in Afghanistan.
Best they start repairing the dam and resuming daily structural maintenance. Dam is built on gypsum and it erodes daily with a continual threat of collapse inherently present:
http://www.danielpipes.org/5107/saddams-damn-dam-ie-the-mosul-dam
The Lakota Sioux were probably the finest light cavalry the world has ever seen. Armed with nothing more than repeating carbines, mounted on mustang ponies, they could hold off and send into retreat much better armed and equipped US Cavalry troops, even battled-hardened Civil War veterans.
In one of the most famous routs in the history of Indian Wars on the frontier, the Battle of Little Bighorn, the Lakota, Northern Cheyenne, and Arapaho tribes combined to wipe out, to the last man, the advance of General George Armstrong Custer, who made the mistake of thinking his command could engage and defeat what they thought was a much smaller force.
In many ways, the Kurds are as much as fierce fighters as the Lakota Sioux Indians, and they are highly motivated.
This time, the US military should back the right side.
If the IS guys don’t blow the dam while they still have access to it , it is likely because they haven’t figured out how to do it. The results would be spectacular if they did it and would bring them more hordes of eager recruits.