ABOARD A MILITARY AIRCRAFT — The U.S.-led coalition launched one of the largest airstrikes yet on an Islamic State car bomb factory Thursday night, hitting a sprawling compound south of Mosul with aircraft dropping dozens of bombs.

The airstrike was the culmination of months of intelligence gathering and is part of a broad effort to weaken militants in Mosul in advance of a U.S.-backed offensive to recover Iraq’s second-largest city from the Islamic State.

The U.S. Air Force allowed a reporter to fly in a surveillance aircraft over Syrian airspace as the planes attacked the targets in neighboring Iraq.

The Airborne Warning and Control System (AWACS) plane monitors radio traffic and provides radar coverage in crowded airspace above Iraq and Syria, coordinating among coalition planes and issuing warnings if Russian or Syrian aircraft appear heading near allied operations.