Gulf of Tonkin incident:

The United States government falsely claimed that a second incident occurred on August 4, 1964, between North Vietnamese and United States ships in the waters of the Gulf of Tonkin. Originally, US military claims blamed North Vietnam for the confrontation and the ostensible, but in fact imaginary, incident on August 4. Later investigation revealed that the second attack never happened. The official American claim is that it was based mostly on erroneously interpreted communications intercepts.[5][6] The National Security Agency, an agency of the US Defense Department, had deliberately skewed intelligence to create the impression that an attack had been carried out.[7][8][9]“