of available communications channels, which allowed the seeding of a larger sensor field without fear of signal interference. By 1971–1972 a new sensor with a commandable microphone (COMMMIKE III) and another with a vehicle ignition detector (EDET III, which could detect the unshielded ignition systems of gasoline engines) were introduced. In 1972 U.S. dollars the ADSID cost $619.00, the ACOUSID $1,452.00, and the engine detector $2,997.00. During the life of the operation approximately 20,000 sensors were deployed in Laos. Analysis of sensor results The sensor transmitters would relay their data to the second element of the system, an orbiting EC-121R aircraft of the Air Force's 553rd Reconnaissance Wing, based at Korat Royal Thai Air Force Base. The EC-121s would then relay the collected information via a radio link at 2200 to 2300 MHz to Nakhon Phanom. At Task Force Alpha, the last of the three components in the system, the intelligence data (from a variety of sources, not just the sensors) would be entered, collated, retrieved, and stored by two IBM 360/40 (later two 360/65) computers. Technicians at the center controlled the system from a variety of video displays that were also linked to the computers. Analysts at the center concentrated on such arcane topics as pathway predictions, delay intervals, route segments, and choke points. The computers analyzed sensor data and compiled intelligence information and then made predictions as to where and when a particular PAVN truck convoy would be geographically located. According to author John Prados, the system functioned "exactly like a pinball machine... in truth, the mavens of the electronic battlefield became pinball wizards". The effectiveness of the system was determined not by how long a sensor would last in the field, but by the adequacy of coverage by a particular string of sensors. For instance, a well placed string with several failed sensors was more effective than a fully functional string placed in the wrong location. The electronic data was, however, only as good as the human analysts and operators at the ISC. The knack of timely sensor activation depended on careful study of device locations and the patterns of PAVN logistical behavior. The sensors were delivered to the target areas by U.S. Navy OP-2 Neptunes of VO-67 or by U.S. Air Force helicopters, both based at Nakhon Phanom. Due to increasing PAVN anti-aircraft artillery defences encountered in southeastern Laos, delivery in high-risk areas of the trail