This chapter focuses on the covert side of the Vietnam War. Secrecy famously helped Richard Nixon cope with dovish domestic opposition toward the end of the war. In contrast, the chapter highlights the role of covert intervention in helping both sides compete in Vietnam while keeping the war limited during the earlier Johnson years (1964–1968). Even as he greatly expanded U.S. military activity in Vietnam, President Lyndon Johnson acted to avoid provoking a larger war with China or the Soviet Union. Covert U.S. military operations in places like Laos, though an open secret, were a way to prosecute a counterinsurgency while keeping a lid on hostilities. China and the Soviet Union similarly sought to control escalation dangers through covertness. Both communist patrons provided military personnel covertly to improve air defense in North Vietnam. The chapter suggests that all three outside powers worked hard to avoid public and acknowledged clashes up through 1968.