December 30, 2004
Igloo White
It began (in 1967) as “the McNamara Line” across Vietnam. It led to the seeding of the Ho Chi Minh Trail by air with 20,000 sensors.
Igloo White consisted of three parts: the sensors, the orbiting aircraft to relay the signal, and the Infiltration Surveillance Center at Nakhon Phanom Air Base in Thailand.
An airman gets ready to hurl a seismic sensor from an HH-3 helicopter over Vietnam to form part of the electronic infiltration barrier...
The sensors...were planted mostly by Navy and Air Force airplanes, although some of them were placed by special operations ground forces. They were dropped in strings of five or six to be sure that at least three sensors in each string would survive and be activated. The sensors operated on batteries, which ran down after a few weeks, so replacement sensors had to be dropped.
Most of the sensors were either acoustic or seismic. There were two kinds of acoustic sensors, both derived from the Navy’s Sonobuoy, to which microphones and batteries were added. These sensors could hear both vehicles and voices.