One of the least conspicuous, but most fascinating displays at the National Museum of the United States Air Force at WrightPatterson AFB in Dayton, Ohio is this exhibit of A.D.S.I.D. (Air Delivered Seismic Intrusion Detector) devices. These were employed during Operation Igloo White, the clandestine, remote surveillance and intelligence gathering operation along the Ho Chi Minh Trail in North Vietnam, Laos, Cambodia and into South Vietnam beginning in 1967.