The first Grand Slam (22,000-pound) bomb is dropped from an Avro Lancaster flown by Royal Air Force Squadron Leader C.C. Calder. Two spans of the Bielefeld railway viaduct in Germany are destroyed.
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.
