The Gulf of Tonkin incident refers to a naval confrontation in the Gulf of Tonkin off the coast of North Vietnam, which led to the United States engaging more directly in the Vietnam War. On 2 August 1964 there was a clash between a destroyer of the United States Navy that was collecting signals intelligence close to North Vietnamese waters, and three North Vietnamese naval vessels. On the night of 4 August, two US destroyers reported they were attacked by North Vietnamese vessels and that they were returning fire. Later investigation revealed that the 4 August attack did not happen; no North Vietnamese vessels had been present. Shortly after the events, the National Security Agency, an agency of the US Defense Department, deliberately skewed intelligence to create the impression that an attack had been carried out.