<p>In June 1968, a single squadron of F-4Ds with special modifications, including LORAN navigational equipment, took over the sensor drops. The Phantoms carried the sensors in various mixes, but generally 16 in each SUU-42/A pod dispenser hung on the outboard wing stations. Typical delivery speed was 300 to 350 kt (550 and 645 km/h). As it turned out, the LORAN system was not that accurate, but for nighttime and all-weather placing of the sensors there was no alternative.
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<p>On the ground 100 miles (160 km) away in Laos, Task Force Alpha, a special USAF unit established for Igloo White, had built its Infiltration Surveillance Center (ISC). It was a complex, computerized ground station that received, processed, displayed and transmitted the data and its analysis. Between the sensors on the Trail and the ISC was an orbiting relay aircraft, a dedicated Lockheed EC-121R; it was necessary because the sensor transmissions propagated along lines-of-sight and the ISC was, obviously, out of sight of the Trail. The EC-121R also had the equipment necessary to assess the sensor information, as a backup to the ISC. There was a further backup, the Deployable Automatic Relay Terminal (DART), which had no computers, but enough displays of sensor output to enable an experienced operator to make a real-time evaluation of the situation and to act on that assessment.
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<p>Because of the possibility that the EC-121R could become a sitting duck in the event the NVAF really decided to go get it, there was a backup aircraft program, designated Pave Eagle. That program developed a stock Beech Debonair into a piloted or droned relay aircraft with a more powerful engine and increased wingspan. It was also dedicated to relay Igloo White communications, it was more economical to operate than the big four-engined Lockheed, and it could operate as a drone in a high-risk area.
