The PAVN transformed the A Shau Valley into a heavily fortified base area with bunkers, antiaircraft guns, and artillery. US and South Vietnamese forces were never able to re-establish a permanent presence in the valley for the remainder of the war. During the Tet Offensive the A Shau Valley provided Communist troops an important sanctuary from which to launch attacks at South Vietnamese cities and military bases, especially Huế and Phu Bai. Raids were launched into the valley in April 1968 (Operation Delaware), August 1968 (Operation Somerset Plain), March 1969 (Operation Dewey Canyon) and May 1969 (Operation Apache Snow).