Operation Northern Watch, conducted out of Incirlik Air Base, Turkey, flies its last mission over Iraq. The operation includes 36,000 sorties. It formally ends on May 1.
The U.S. began extensive air and artillery strikes against Islamic State group targets in Syria on Dec. 19 in retaliation for the killing of three Americans on Dec. 13 by a gunman affiliated with ISIS, U.S. officials said.

