The United States was going to launch an automatic and all-out nuclear attack on both the Soviet Union and China, in the event that the President was killed in an attack, a newly released document reveals. The plan was in place until 1968, when the plan was revised by President Johnson. It went by the name "Furtherance." Here's how William Burr of the National Security Archive at George Washington University described the state of play before the changes.
Prior to President Johnson's decision, instructions for the emergency use of nuclear weapons that both he and his predecessors had previously approved stipulated a full-scale nuclear counter-attack even if the initial strike were conventional, or the result of an accident, and both Communist giants would be targeted regardless of whether either of them had launched the first strike.