The first mission of “Big Week”-six days of strikes by Eighth Air Force (based in England) and Fifteenth Air Force (based in Italy) against German aircraft plants -is flown.
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.

