It was the last major offensive conducted by the U. S. Marine Corps during the Vietnam War. It involved over 2,200 Marines. It began January 22, 1969 and lasted through March 18th in the A Shau Valley just six miles east of the Vietnam-Loas border along the "Ho Chi Minh Trail." It involved the 9th Marine Regiment with reinforcements from the 3rd Marine Regiment and additional support from the U. S. Air Force. The 56 day combat operation was designed to "sweep" the North Vietnamese Army from the 21 long mile valley. The operation was divided into three parts and was a tactical success. The 9th Marines and attached units were awarded the Army Presidential Unit Citation for their actions. Encountering stiff resistance, 130 U. S. Marines were killed in action during the operation and over 900 more were wounded. The enemy losses were estimated at over 1,600 killed. Corporal William D. Morgan, LCpl Thomas P. Noonan, Jr., and PFC Alfred M. "Mac" Wilson were all posthumously awarded the Medal of Honor for their heroism during Operations Dewey Canyon.