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