An operation designed to provoke the North Vietnamese into attacking the South and US interests in the area. This would allow the US to increase its response to the NVs, causing the US to enter into the war.
How true is this?
Given that the Vietnam War began in November 1955 (at least the American part) and Farm Gate 13 January 1962 this assumption is false. North Vietnam had already begun to support and train guerilla forces before CIA clumsy and largely fruitless involvement in Farm Gate.