Tonkin Gulf resolution, in U.S. history, Congressional resolution passed in 1964 that authorized military action in Southeast Asia. On Aug. 4, 1964, North Vietnamese torpedo boats in the Gulf of Tonkin were alleged to have attacked without provocation U.S. destroyers that were reporting intelligence information to South Vietnam. President Lyndon B. Johnson and his advisers decided upon immediate air attacks on North Vietnam in retaliation; he also asked Congress for a mandate for future military action. On Aug. 7, Congress passed a resolution drafted by the administration authorizing all necessary measures to repel attacks against U.S. forces and all steps necessary for the defense of U.S. allies in Southeast Asia. Although there was disagreement in Congress over the precise meaning of the Tonkin Gulf resolution, Presidents Johnson and Richard M. Nixon used it to justify later military action in Southeast Asia. The measure was repealed by Congress in 1970. Retired Vietnamese general Vo Nguyen Giap, in a 1995 meeting with former Secretary of Defense Robert McNamara, categorically denied that the North Vietnamese had attacked the U.S. destroyers on Aug. 4, 1964, and in 2001 it was revealed that President Johnson, in a taped conversation with McNamara several weeks after passage of the resolution, had expressed doubt that the attack ever occurred.