Hundreds of Syrian fighters and their U.S. advisers were airlifted by U.S. helicopters across enemy lines on Tuesday and Wednesday in a bold operation to cut off the western approaches to Raqqa, the self-proclaimed capital of ISIS.

It was the first time the U.S. has carried out an air assault in its campaign against the Islamic State in Iraq and Syria.

It reflected the leeway the Trump administration has given its commanders to carry out operations without prolonged review in Washington.