Hundreds of U.S. troops backed by helicopters launched a major operation in southern Afghanistan on March 20, 2003 in an apparent signal to Afghan rebels the U.S. Army would not be distracted by war in Iraq. 'The White Devils of Coalition Task Force 82 began Operation Valiant Strike with an air assault at 6 a.m.,' the U.S. military said in a statement issued at Bagram Air Base, its headquarters in Afghanistan.