Nathan Freier is an associate professor at the US Army War College who was deployed in Iraq as a lieutenant colonel at the height of the Bush era "surge." He said the ISIS forces are clearly benefiting from the American weapons they've captured. "They are assembling more capability at the hands of a collapsing Iraqi security structure," he said. "To the extent that they can bring a tank or heavy machine guns to bear, that's going to be a problem for the people they run up against."
But Freier cautioned that the weaponry doesn't automatically make ISIS the dominant force on the battlefield. "They're not going to suddenly assemble an armored division," he said. "Their competence in deploying that equipment in a sophisticated manner is highly questionable."
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The specter of U.S. equipment being turned against U.S. interests can be deeply frustrating to military experts. "We're going to be bombing our own equipment," said retired Gen. Barry McCaffrey.
Referring to a U.S. airstrike announced against ISIL guns Friday morning, he said, "That artillery piece was likely have been supplied by the U.S. to the Iraqi Army, although it could have been old Soviet equipment, too."
"Somewhere between two and four of the Iraqi Army divisions—out of 14—took off," McCaffrey said. "Their general went back to Baghdad, and the soldiers all took off."