Second-generation Army Tactical SIGINT Aircraft (continued)
LAFFING EAGLE increased RU-21 series capability by adding a second SIGINT operator, receivers with a greater frequency range, and an AN/ASN-86 Internal Navigation System. The new system proved very difficult to maintain, however, requiring constant support from contractor representatives and a 40-foot (12 m) trailer full of test equipment. Later on, the V-SCAN system, which gave 240-degree direction-finding coverage centered around the nose and tail, was added to the RU-21Ds. Those aircraft arrived in Vietnam in December 1968 and heavily used.
WINE BOTTLE and CEFISH PERSON systems, on RU-6A and RU-8D aircraft, were generally unsatisfactory and the 156th Radio Research Company, using these aircraft, redeployed to the US. These aircraft were incapable of true goniometric ARDF, and had to fly over the emitter, dangerously, before pinpointing it.
MASINT sensors to "fingerprint" equipment and operators, first coded SHORT SKIRT and then LEFAIR KNEE, went onto 12 RU-8D airplanes. They were assigned to the 509th Radio Research Group, although some were detached for a time. Some received side-looking airborne radar (SLAR), a MASINT RADINT sensor that later became standard on the OV-1B Mohawk.
LEFT BANK, introduced in 1970, was a first attempt for 360-degree coverage, which was perfected as LEFT JAB on the JU-21A series. LEFT JAB was the first Army system that used an airborne digital computer to combine DF and inertial navigation information. The next refinement, LEFT FOOT, combined the LAFFING EAGLE's sharper DF feature with the LEFT JAB computer, creating the RU-21E aircraft. Very few LEFT FOOT aircraft flew in Vietnam.
CEFIRM LEADER, first known as CRAZY DOG, was an attempt to build a system, called V-SCANARDF, the combined intercept, direction finding, and jamming for the 2-80 MHz frequency range. Implementation involved one of the features to appear in the much later Guardrail series, using several aircraft in a team. RU-21A's carried AN/ARD-22 direction finders. RU-21B's were COMINT intercept aircraft with the AN/ALT-32. RU-21C's carried AN/ALT-29 jammers. The system never worked well, although RU-21D and RU-21Es got it working, and served into the 1990s.
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