TIMELINE-Deadliest days for U.S. troops in Iraq

(Reuters) - 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.