Improvements in radar stealth have reached a point where visual and infrared signatures are the dominant concerns. One sign of increasing interest in the non-radar aspects of stealth is that the Air Force has commissioned a new flying laboratory called FISTA II (Flying Infrared Signature Technology Aircraft), to replace a vehicle that has been used since the early 1960s to measure the heat signatures of airplanes. A modified tanker aircraft, FISTA II carries not only ultrasensitive infrared imagers, bit also a visual

imaging system, an indication that the Pentagon is becoming serious about visual stealth. Modern follow-ons to Yehudi are both more effective and easier to install. Instead of individual lights, the Pentagon has tested thin fluorescent panels of the type already used on military aircraft for nighttime formation flying. A civilian technician working at the isolated Tonopah Test Range airstrip in Nevada says he witnessed a test of an F-l5 Eagle with a prototype system. According to the

technician, thc fighter virtually disappeared as it lifted off the runway. "We had no problem acquiring the aircraft from about a mile away," the technician recalls, "but at distances over two miles it became harder and harder to spot. Although it was a crude system, it was pretty impressive. Trying to pick out the aircraft against a clear blue sky was next to impossible. The only time we could easily spot the aircraft was when it produced an unexpected contrail." (Contrails form when the water vapor in aircraft exhaust freezes.