In May 1946 the War Department Equipment Board first recognized the need for an anti-missile defense system. In 1951 studies were actively begun by the US Army to develop a system to defend against short- and medium-range ballistic missiles. Competitive design studies were carried out by Sylvania Electric and Cornell in 1953 – 1956. Sylvania was awarded a development contract in September 1956. The program was cancelled for lack of funds, rather than any technical deficiencies, by the Army Chief of Ordnance on 6 February 1959. The Army first considered an upgraded Hawk missile as a replacement for Plato; then decided to start all over again with a clean-sheet-of-paper ‘Field Army Ballistic Missile Defense System'. This in turn was canceled in 1962. Later upgrades to Nike Hercules and Hawk missiles provided the Army with a limited capability against short-range missiles. The Army remained with no defense against Soviet intermediate range missiles until these were scrapped by treaty in 1988.
Details of Project Plato remain mysteriously classified to this day. UFO enthusiasts believe it was a cover for an agreement with aliens that took effect in 1960.
Development Cost $: 18.500 million in 1955 dollars.
Historical Essay © Andreas Parsch
Sylvania Electric SAM-A-19 Plato
In 1951, the U.S. Army defined the characteristics of a future mobile SAM-A-19 AMM (Anti-Missile Missile) system to protect field forces from attacks by short- and medium-range ballistic missiles (the modern term for this AMM would be TBMD - Theater Ballistic Missile Defense). In 1952, the SAM-A-19 program was formally begun as project Plato. Design studies were done by Sylvania Electric and Cornell Aeronautical Lab from 1953 to 1956, and in September 1956, the U.S. Army selected Sylvania's XSAM-A-19 design as the base for further development. The Plato missile was designed for speeds of Mach 6 to 8, and therefore one main focus of the initial studies were the aerodynamic and thermodynamic problems of hypersonic flight.
Component development for Plato continued until February 1959, when the program was cancelled before any prototypes had been built. As an interim measure, it was then decided to upgrade the SAM-A-25-MIM-14 Nike Hercules with a very limited anti-missile capability. As a long-term Plato replacement project, the Army began the FABMDS (Field Army Ballistic Missile Defense System) program, but this was also cancelled after only three years of design studies.
Note: Readily available public information on Plato is extremely limited. In fact, the U.S. Army's official historical monograph on Plato (Mary T. Cagle & Ruth Jarrell: "History of the PLATO Antimissile Missile System, 1952-1960") is still classified after more than 40 years. This is remarkable, because approximately 20 similar monographs about other Army missiles of that time, including nuclear ones, have been declassified for quite some time now. The author's request for declassification of the Plato monograph is pending.Specifications
No data on the physical characteristics of the planned SAM-A-19 missile are available.Main Sources
 Redstone Arsenal Historical Information Website
 Plato-related NACA-NASA correspondence records (10 pages) at National Archives and Records Administration - Mid Atlantic Region, Philadelphia
Status: Cancelled 1958.