This campaign was mainly concerned with the Allied incursion into Cambodia, codenamed Operation ROCK CRUSHER.

     As American withdrawal from South Vietnam proceeded, increasing concern arose over the enemy's strength in the sanctuaries inside Cambodia. With the emergence in Cambodia of an anti Communist government under Lon Nol, President Nixon relaxed the restrictions on moving against the bases inside Cambodia. Meanwhile, the North Vietnamese and Viet Cong began to move on the Cambodian capital of Phnom Penh. At this juncture Lon Nol appealed to the United States for help.

     American and allied Vietnamese forces began large-scale offensives in Cambodia on 1 May. Eight major US Army and South Vietnamese operations took place in Cambodia in May and June with the object of cutting enemy communication lines, seizing the sanctuary areas and capturing the shadowy Central Office for South Vietnam (COSVN) described as the control center for enemy military operations against III CTZ.