UWAIT, April 26 — For America's Special Operations forces, the war in Iraq almost started with a disaster. On March 18, three MH-53 Pave Low helicopters swept low and fast through the night toward a landing zone in the southern Iraqi desert. In their bellies were Toyota pickup trucks carrying Army Special Forces soldiers: the unconventional vanguard of an invasion that was to begin in two days.But in the swirling dust, one of the helicopters clipped a rock outcropping as it tried to land. The aircraft whirled about like a bucking bronco before crashing on its side in a...