History of the IRON HORSE system

In 1967 the United States SIGINT system (USSS) improved the speed of its support to air operations over Vietnam by a quantum leap. The older manual system, HAMMOCK, was replaced by IRON HORSE, a flashy new automated system which could deliver information in seconds rather than minutes.

Designed by the National Security Agency, IRON HORSE simply linked the electronic output of an AG-22 intercept position, through a computer, to a radar scope. Instead of using a plot-tell system for calling aircraft positions to the TACC or CRC, the computer would convert the grid plot to a geographical coordinate and display it on a radar scope.

Plots from SIGINT that went to the CRC, Task Force 77, and the Marines had a unique signature that identified them as not derived from American radar. IRON HORSE decreased intercept time from twelve to thirty minutes to anywhere from eight seconds to three minutes. It was state-of-the-art and about as fast as Morse tracking could be displayed.


I found a partially declassified history of the IRON HORSE system in a shred pile of mine. I uploaded this to Internet Archive for safe(r) keeping on the Internet. Enjoy the read!

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