Since the recapture of the northern Iraqi town of Baiji last October, Islamic State defenses have crumbled rapidly across a wide arc of territory. In Syria, the important hub of Shadadi was recaptured with little resistance in February, while in Iraq, Sinjar, Ramadi, Hit and, most recently, the town of Bashir have fallen in quick succession, lending hope that the militants are on the path to defeat.

“So far, in terms of what we had hoped to do, we are pretty much on track,” said a U.S. official who spoke on the condition of anonymity in order to discuss sensitive subjects. “We’re actually a little bit ahead of where we wanted to be.”

The fight, however, is entering what Pentagon officials have called a new and potentially harder phase, one that will entail a deeper level of U.S. involvement but also tougher targets.

In an attempt to ramp up the tempo of the war, the U.S. military is escalating its engagement, dispatching an additional 450 Special Operations forces and other troops to Syria and Iraq, deploying hundreds of Marines close to the front lines in Iraq and bringing Apache attack helicopters and B-52s into service for the air campaign.