The following are events related to the Global War On Terrorism (GWOT) that took place on this day.

2003

• A Marine CH-46 Sea Knight helicopter from Marine Medium Helicopter Squadron 268 crashed nine miles south of Umm Qasr. All four Marine crewmembers and the eight Royal British Marines they were ferrying became the first to be killed in Operation Iraqi Freedom. There was no indication of hostile fire.
• Start of Battle of Umm Qasr in Iraq
• 3d Infantry Division attacks Tallil Air Base and As Samawah on the road to Baghdad

2006

• Start of Operation Northern Lights in Iraq

2007

• Major William D. Chesarek, Jr., was awarded the British Distinguished Flying Cross (DFC) in a ceremony at Buckingham Palace, London, by Queen Elizabeth II. Major Chesarek was serving as an exchange office with the British 847 Naval Air Squadron and was deployed to Iraq with that unit. His actions on 10 June 2006 supporting British ground troops lead to him becoming the first American since World War II to receive a British DFC.

Casualties on March 21:

• AUBIN, JAY THOMAS – March 21, 2003
• BEAUPRE, RYAN ANTHONY – March 21, 2003
• CHILDERS, THERREL SHANE – March 21, 2003
• GUTIERREZ, JOSE – March 21, 2003
• KENNEDY, BRIAN MATTHEW – March 21, 2003
• WATERS-BEY, KENDALL DAMON – March 21, 2003
• HUDSON, CHRISTOPHER EDWIN – March 21, 2004
• KREIDER, DUSTIN LEVI – March 21, 2004
• SMITH, KEVIN SCOTT – March 21, 2005
• MCKINZIE, ANTOINE JAY – March 21, 2006
• GRIFFIN, DARRELL RAY JR – March 21, 2007
• LEE, DUSTIN JEROME – March 21, 2007
• LEWIS, ADRIAN JUANCITO – March 21, 2007
• LIGHTNER, NICHOLAS JAMES – March 21, 2007
• SAMS, JOEY TYRONE II – March 21, 2007
• MAUPIN, KEITH MATTHEW – March 21, 2008
• SMITH, TYLER JACOB – March 21, 2008
• HOCKING, BRANDON SCOTT – March 21, 2011
• JARBOE, JAMIE DARRELL – March 21, 2012
• GRISSOM, JAMES FLOYD – March 21, 2013