Guardrail Product Improvement Program
The Guardrail II and IIA systems were part of a product improvement program for the initial Quick Reaction Capability (QRC) Guardrail I system. An important operational need, not provided by Guardrail I, was the ability to locate the position of enemy communications. Conveniently, ESL was performing flight test demonstrations for the Army Security Agency (ASA) on an IR&D developed, patented, simple, electronic direction finding system in the late 1971 and early 1972 time frame. ESL felt that a remote version of this direction finding system could be manufactured and integrated in time for the 1972 REFORGER exercises. The Guardrail II product improvement program was authorized in April of 1972. Guardrail II was to use as much of the initial Guardrail system as practical. Once again, the delivery schedule was 5 months.
Integration of airborne direction finding system required an inertial navigation system. The solution was to use the residual Left Foot RU-21E aircraft that had already integrated the AN/ASN-86 inertial navigation system and add antenna foot prints required for the Guardrail direction finding array. The original Guardrail I microwave link required moderate upgrades to support direction finding link requirements. The air-to-air relays and TCT relay were upgraded from VHF to UHF for less interference. Digital protocol was added to the TCT to allow for a direct computer interface of emitter location direction finding data into reports and for keyboard free text inputs to the TACREP's.
A computer system and mission peculiar software were required to support direction finding commands, calculations, and reporting. The computer map/hard copy capability provided overlay of lines of bearing on map coordinates. The computer also provided spheroid earth curvature calculations required to formulate target locations based on direction finding line of position measurements. The Guardrail II system was now able to perform instant direction finding against acquired targets with a simple key stroke. An Auxiliary Ground Equipment (AGE) facility was configured in a Ford Econoline van for basic flight line checkout of prime mission electronics.
Initially, the intent was not to field the QRC Guardrail II system as a permanent operational system due to a lack of logistic support. Only a very limited "push package" of spares were available at that time. Additional spares and minor enhancements were incorporated under a further product improvement program, known as Guardrail IIA. Guardrail IIA remained as a US Army, Europe (USAREUR) theater asset until the arrival of Guardrail V some 6 years later. It participated in all subsequent REFORGER exercises. The forces that had the Guardrail system had the advantage on the battlefield. The advantage was that the tactical commander now had critical intercepted COMINT data that reached beyond the forward line of troops (FLOT). That data was effectively used by the commanders to help formulate, implement and adjust their battle plan.
Guardrail II and IIA served in Europe, along with Guardrail I, until the introduction of the Guardrail V system in the late 1970s.
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