 During a televised address on 20 April , Nixon announced the withdrawal of 150 @,@ 000 U.S. troops from South Vietnam during the year . This planned withdrawal implied restrictions on any offensive U.S. action in Cambodia . By the spring of 1970 , MACV still maintained 330 @,@ 648 U.S. Army and 55 @,@ <unk> Marine Corps troops in South Vietnam , most of whom were concentrated in 81 infantry and tank battalions . Many of them , however , were preparing to leave the country or expected to leave in the near future and would not be available for immediate combat operations . 
