Cable 243 is Sent to Henry Cabot Lodge, Jr., the US Ambassador to South Vietnam

DEPTEL 243, also known as Telegram 243, the August 24 cable or most commonly Cable 243, was a high profile message sent on August 24, 1963 by the United States Department of State to Henry Cabot Lodge, Jr., the US ambassador to South Vietnam.

The cable came in the wake of the midnight raids on August 21 by the Catholic regime of Ngo Dinh Diem against Buddhist pagodas across the country, in which hundreds were believed to have been killed. The raids were orchestrated by Diem's brother Ngo Dinh Nhu and precipitated a change in US policy. The cable declared that Washington would no longer tolerate Nhu remaining in a position of power and ordered Lodge to pressure Diem to remove his brother. It said that if Diem refused, the Americans would explore the possibility for alternative leadership in South Vietnam. In effect, the cable authorized Lodge to give the green light to Army of the Republic of Vietnam (ARVN) officers to launch a coup against Diem if he did not willingly remove Nhu from power. The cable marked a turning point in US-Diem relations and was described in the Pentagon Papers as "controversial". Historian John W. Newman described it as "the single most controversial cable of the Vietnam War."

The cable also highlighted an internal split in the Kennedy administration, with anti-Diem officials in the State Department prevailing over generals and Department of Defense officials who remained optimistic that the Vietnam War was proceeding well under Diem. This was underlined by the manner in which the cable was prepared before being transmitted to Lodge.