Army Regulation 670-1, Wear and Appearance of Army Uniforms and Military Insignia, specifies that branch scarves may be worn with the Army Service Uniform and the utility uniform for ceremonial occasions when prescribed by the local commander. Per Department of the Army Pamphlet 670-1, members of the Chemical Corps are issued a bib-style scarf in the Corps’ first-named branch color, Cobalt Blue.
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Detection is the linchpin of Chemical, Biological, Radiological, and Nuclear (CBRN) defense doctrine. Without it, the other three pillars of CBRN defense—avoidance, protection, and decontamination—are either worthless or greatless reduced in their efficacy. But for a period in the 1960s, the Chemical Corps was tasked with using its scientific expertise to detect a different type of threat than radiation, chemical agents, or bioweapons: People.
A major problem facing the U.S. Army during the Vietnam War was finding a way to shut down the flow of men and matériel moving from North to South Vietnam via the Ho Chi Minh Trail. One of the first techniques the Army employed was having the Chemical Corps spray herbicides along the route to defoliate the area and make it easier for aerial reconnaissance units to spot convoys and troops. The problem with such an approach, however, is that North Vietnamese weren’t oblivious to the fact that they were no longer protected from overhead observation by a jungle canopy. Another issue was that defoliated areas would regrow during the next rainy season.
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So the Chemical Corps took a different tact based on the concept that detecting the presence of something inextricably linked to the presence of people was just as effective as detecting the people themselves. And, appropriately enough, that something they were searching for was a chemical: the ammonia found in human perspiration. Scientists at General Electric developed a “people sniffer” device based on the principle that the ammonia found in human sweat, when combined with hydrochloric acid, forms ammonium chloride, which in turn can be detected in a cloud chamber. Armed with the first people-sniffer device—the XM2 Personnel Detector Manpack—Soldiers in the Chemical Corps began what was later dubbed “Operation Snoopy.”
The XM2 system, however, had a couple of drawbacks. Featuring an air-intake tube positioned at the end of a rifle, the XM2 was incapable of distinguishing between the “effluents”—i.e., sweat—of enemy soldiers and that of the Chemical Corps soldiers carrying the manpack. And the systems’ tell-tale ticking sound sometimes served to help the North Vietnamese detect Corps soldiers wielding the devices.
A helicopter-mounted system, the XM3 Airborne Personnel Detector, eliminated both issues. Protected by helicopter gunships flying behind and above it, a chopper carrying the XM3 would take take three dozen or so air samples for analysis to set background or naturally occurring levels of effluents, then use it as a baseline for detecting the presence of enemy troops. Best results were obtained when winds were under ten miles per hour, and midday collection was the most fruitful period when working over jungle terrain. It as particularly effective durin gthe rainy season because the precipitation tended to wash away “background” effluents that could distort analysis.
The system wasn’t perfect, of course, and the North Vietnamese took countermeasures—not firing on “Snoopy” missions, creating decoy effluents with buckets of urine, starting fires to overload and confuse sensors—but in the end it was deemed second-most reliable means of enemy troop detection, surpassed only by visual sightings.