Igloo White By Using the cover of darkness, dense jungle and bad weather, North Vietnamese trucks carried critical supplies down the Ho Chi Minh Trail nearly undetected. Since large numbers of American ground troops were not permitted into neutral Laos to stop the trucks, the U.S. Air Force deployed a system of electronic equipment to thwart the enemy's cover and alert U.S. commanders. This highly-classified electronic system was known as Igloo White. The system became operational in late 1967, and it consisted of three elements: sensors dropped by aircraft along the Ho Chi Minh Trail, an orbiting EC-121B "Batcat" or the QU-22B aircraft that picked up and relayed signals from the sensors, and the Infiltration Surveillance Center (ISC), which received the data. Operated by Task Force Alpha at Nakhon Phanom Royal Thai Air Force Base (NKP RTAFB), the ISC interpreted the sensor data and passed target information to combat commanders, who sent attack aircraft to the target. The Igloo White sensors on display are but a few of the many types employed along the Trail. Some sensors detected seismic disturbances created by passing trucks; some sensors used microphones to pick up nearby voices; and other sensors detected both seismic disturbances and voices. Dropped from F-4 Phantoms, CH-3 helicopters, OV-10s and other aircraft, they were designed to drive into the ground but leave the antenna exposed. The antennas were made to look like a small tree or bush to hide them from the enemy. Over 20,000 sensors were dropped in Laos, and 80 percent of the sensors were operational after dropping. Types of Sensors on Display ADSID (Air Delivered Seismic Intrusion Detector) - Used an internal geophone to detect personnel or vehicles in motion ACOUSID (Acoustic and Seismic Intrusion Detector) - used seismic and acoustic devices; could transmit sound from a built-in microphone HELOSID (Helicopter Delivered Seismic Intrusion Detector) Click here to return to the Laos: The Panhandle and the Ho Chi Minh Trail Overview. Find Out More Related Fact Sheets Beech QU-22B McDonnell Douglas F-4C Phantom II North American Rockwell OV-10A Bronco Note: The appearance of hyperlinks does not constitute endorsement by the National Museum of the USAF, the U.S. Air Force, or the Department of Defense, of the external website, or the information, products or services contained therein.