Leon Panetta replaces Robert Gates at Secretary of Defense. Gates had led the Defense Department since December 2006, serving both President George W. Bush and President Barack Obama. Panetta previously was Director of Central Intelligence.
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.

