Fourteen U.S. soldiers were killed when their helicopter crashed in northern Iraq on Wednesday, the U.S. military said, in one of the worst incidents of its kind in the four-year war.
Here is a chronology of the deadliest days for U.S. forces since the start of the conflict.
March 23, 2003 - On the third day of the war, 28 U.S. soldiers are killed, mostly in fierce fighting in southern Iraq.
-- November 2 - Chinook helicopter is shot down near Falluja. Sixteen U.S. troops killed and 21 others on board hurt.
-- November 15 - Two Black Hawk helicopters collide under fire in Mosul, killing 17 soldiers.
December 21, 2004 - Suicide bomber in Iraqi uniform walks into mess tent at Mosul and kills 21 people, 18 of them Americans, including 14 U.S. troops.
January 26, 2005 - U.S. Marine transport helicopter ferrying troops comes down in western desert, killing 31 aboard. Six more are killed in insurgent attacks.
-- August 3 - Fourteen Marines are killed in a roadside bomb blast on an amphibious assault vehicle near Haditha, northwest of Baghdad. A civilian interpreter is also killed.
-- December 1 - Ten U.S. Marines are killed near Falluja in an insurgent bombing. Another is killed in Ramadi.
January 5, 2006 - Eleven U.S. soldiers are killed in separate incidents, the worst of which is the deaths of five in Baghdad when a roadside bomb hits their patrol.
-- January 7 - Eighteen U.S. soldiers are killed, 12 of whom die when a Blackhawk helicopter comes down near the town of Tal Afar near Mosul, 390 km north of Baghdad.
-- August 27 - Twelve U.S. soldiers are killed in total, mostly in Baghdad.
-- October 17 - Eleven U.S. soldiers are killed in separate incidents around Iraq.
-- December 6 - Ten U.S. soldiers are killed in four incidents around Iraq, some killed by roadside bombs and others in combat.
January 20, 2007 - A U.S. military helicopter goes down northeast of Baghdad, killing 12 people aboard. More soldiers are killed in clashes and roadside bombs. Twenty-five are killed in total.
-- February 7 - All seven crew members and passengers aboard a U.S. Marine transport helicopter are killed when their aircraft crashes in Anbar province. Another four die in other incidents.
-- May 6 - Ten U.S. soldiers are killed in separate incidents around Iraq.
-- June 23 - Eleven U.S. soldiers killed in separate incidents.
-- Aug 22 - A UH-60 Black Hawk helicopter with four crew and 10 passengers crashes in northern Iraq. All aboard are killed. The military says first indications are that mechanical failure is to blame and there is no evidence of hostile fire.