Operation Igloo White - Sensors and Weapons

Sensors and Weapons

The Defense Communications Planning Group's research and development program created an advanced technological system. Muscle Shoals would consist of three interdependent parts. First, there were air-dropped, battery-powered acoustic and seismic sensors. The camouflaged sensors were to be dropped in strings at predetermined geographical points along the PAVN logistical network. Once emplaced, they would serve as tripwires to any movement or activity along the system.

The first sensors utilized by the program were Air-Delivered Seismic Intrusion Detector (ADSID), which had been developed from devices then in use in underground mapping for the oil industry. The device could sense vertical earth motion by the use of an internal geophone and could determine whether a man or a vehicle was in motion at a range of 33 yards (30 m) and 109 yards (100 m) respectively. The first acoustic sensors were developed from the U.S. Navy's Project Jezebel anti-submarine warfare sonobuoys, which recorded and processed sound by the utilization of an audio spectrum analyzer. The first model of seismic detectors (Phase I) outshone their contemporary acoustic types in the quality and quantity of the information they reported. The Phase I models of both the acoustic and seismic sensors were only available for operation in a continuous mode, which meant that under normal conditions, their lithium batteries would function for approximately 30 days.

The Acoustic Seismic Intrusion Detector (ACOUSID), combined the operations of both seismic and acoustic devices, with the added ability to transmit sound from a built-in microphone. The ACOUSID had three switchable detection modes: in the C mode, a line spectrum detector determined the presence of enemy vehicles and had an effective range of 1,094 yards (1,000 m); an I Mode which was activated by sounds picked up by its internal microphone and could detect personnel at a range of 438 yards (401 m); and a B Mode that combined both of the above abilities and operated in a continuous real-time mode of 40 activations per hour with a battery life of 30 days.

The sensors reported their data via radio frequency channels ranging upward from 162.5 megahertz (MHz) to 133.5 MHz on the very high frequency band. 31 channels were assigned to each type of sensor with a 375 kHz separation between each channel. Every channel contained 27 identification codes or addresses which could be set in the field prior to emplacement. Thus, a total of 837 individual sensors (27x31) could be deployed at any one time without signal duplication in a single operational zone.

The deployment of Gravel mines and the Wide-Area Anti-Personnel Mine System became integral parts of the operation. Other weapons were specifically developed or otherwise became associated with the campaign as well. These notably included the BLU-31/B and Mk 36 air-dropped mines, BLU-43/B and BLU-44/B landmine system (Dragontooth), the BLU-72/B fuel-air explosive (Pave Pat), and the BLU-52/A chemical bomb (filled with bulk CS-2 powder). Anti-vehicle operations in support of Muscle Shoals/Igloo White were designated Mud River, while anti-personnel operations received the codename Dump Truck.

PAVN personnel moving on foot through the trail system would be detected by the detonation of air-sown, aspirin-sized, wide-area Gravel mines, which would activate the sensors. Subsequent Bomb damage assessment missions and hand emplacement of sensors and mines in support of Muscle Shoals would be carried out by the reconnaissance teams of the highly-classified Military Assistance Command, Vietnam Studies and Observations Group (SOG). A number of hand emplaced units were developed for this role, including the MICROSID and MINISID, and a device designed to work with either called MAGID, a magnetic detector, designed to be triggered by amounts of metal as small as an infantry rifle.

The sensors were designed for air deployment by either of two means. The first was by parachute, which would hang the devices in trees, where they appeared to be part of the foliage. The second method was the use of gravity, which would drive the spike-shaped device into the ground like a lawn dart, burying all but their antennae, which were designed to appear as weeds. Surprisingly, approximately 80 percent of the air-dropped sensors were found to be operational after delivery.

The second phase of sensor development improved the older models by providing for non-continuous operation as directed by the ISC. They also had the capability of carrying out three separate reporting functions: to report current information (transmitting noises or earth tremors); to keep silent, but to count impulses and respond when queried; or to remain in constant operation like the Phase I models. Their batteries also provided the ability to operate for approximately 15 days longer than the Phase I models (45 days).

During late 1969, Phase IV sensors began to be deployed in-theater. These had a greater number 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. The sensors were not cheap. 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.