The MIM-104 Patriot missile is a surface-to-air missile which is used against aircraft and missiles at all altitudes. It was designed by the Raytheon Corporation as a anti-aircraft missile, but its primary role today is ballistic missile defense.
PATRIOT is the acronym for Phased Array Tracking Radar to Intercept Of Target. (A more far-fetched abbreviation is Protection Against Threats, Real, Imagined, Or Theorized.)
In 1976, the Armys SAM-D (Surface-to-Air Missile, Development) program was renamed the PATRIOT program. The tests at the White Sands Missile Range were successful, and the Patriot was deployed in 1984. Although it served for a while as an anti-aircraft system, it was upgraded in 1984 and changed to a anti-ballistic missile weapon.