The Pacific Theater also required a Guardrail capability, especially in light of the successful deployment of 2 systems to Europe. Beginning in 1973, a low budget, 12 month NSA program provided that capability as the Guardrail IV system. It employed an improved version of the AN/ARC-176 UHF communications data links and a new generation, lighter weight, broader coverage R812 VHF receiver. System coverage and basic system capabilities were basically the same as the Guardrail II, except that the new system used a UHF link exclusively versus a mix of S-Band/UHF links.
The computer system and the software for Guardrail IV, with some adaptations and improvements, was derived from Guardrail II. The new system also had a more sophisticated set of AGE that was installed in a step van for self contained flight line maintenance. This expanded AGE concept proved very valuable for efficient permission tests as did the improved Guardrail Integrated Processing Facility (IPF) self test features.
Due to budget constraints, only 4 sets of payloads were delivered with Guardrail IV, along with 6 modified RU-21E aircraft. The system performed very effectively in the Korean environment with the US Eighth Army and enjoyed a reputation for system availability near 100 percent. It operated in Korea until the system was retired in 1979 when it was replaced by the new Guardrail V system.
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