Paratroopers of the 173rd U.S. airborne brigade make their way across the Song Be River in South Vietnam en route to the jungle on the North Bank and into operation Sioux City in the D Zone on Oct. 4, 1966. Troopers and equipment were flown in by helicopter to the central highlands area, but the choppers couldn't land in the D zone jungles. The operation began late in the week of September 25. (AP Photo)