For the first time since the start of the war against the Islamic State terror group, the U.S. military deployed American-trained Syrian forces via helicopter outside Raqqa -- a tactic known as an "air assault," a military spokesman said.
The U.S.-backed Syrian Arab forces landed on American military helicopters with Apache gunships flying overhead.
The indigenous forces were accompanied by U.S. special operations "advisors," the spokesman added.
“It takes a special breed of warrior to pull off an airborne operation or air assault behind enemy lines,” said Col. Joe Scrocca “There is nothing easy about this – it takes audacity and courage. And the SDF (Syrian Democratic Forces) has that in spades.”
"This is pretty major," said the spokesman discussing the operation with reporters on a conference call.
The operation unfolded in Tabqa, Syria, where a few hundred ISIS fighters control a dam. One of the goals of the operation is to take back control of the dam from ISIS. The operation is expected to take "weeks," according to the U.S. military spokesman.
The military official would not comment on specifics of the operation.
"We'll let ISIS figure that out," he said.
A Marine artillery battery on the ground in Syria fired rounds in support of the operation, the U.S. military spokesman said.
Over the last four months, the coalition has conducted more than 300 airstrikes around Tabqah and near Raqqah that have killed hundreds of enemy fighters, destroyed more than 200 fortifications, and more than 50 ISIS vehicles, according to a statement from the U.S. military.
Separately, the U.S. military is looking at reports a U.S. coalition airstrike hit a school in Syria where reportedly 50 Syrian families had taken refuge. The American military said it conducted strikes around Raqqa, and is investigating the matter, but would not confirm it hit the school.
Lucas Tomlinson is the Pentagon and State Department producer for Fox News Channel. You can follow him on Twitter: @LucasFoxNews