Mockup of XM-2 people sniffer on UH-1 aircraft

People sniffer was the field name for a series of U.S. Army issued "personnel detectors" used during the

Vietnam War The Vietnam War (1 November 1955 – 30 April 1975) was an armed conflict in Vietnam, Laos, and Cambodia fought between North Vietnam (Democratic Republic of Vietnam) and South Vietnam (Republic of Vietnam) and their allies. North Vietnam w ...

. The purpose was to detect enemy soldiers in hidden positions, which were often employed in the jungle combat conditions of Vietnam. The U.S. military used two different versions of the people sniffer, one backpack version and one helicopter-mounted version.

Detection method

The detection method used by people sniffers depended on chemical compounds that are emitted only by human beings, such as those found in urine and sweat.Pisor, Robert. ''End of the Line: The Siege of Khe Sanh'', W. W. Norton & Company, 1982,
p. 57
accessed October 24, 2008. The technology was developed by

General Electric General Electric Company (GE) was an American Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1892, incorporated in the New York (state), state of New York and headquartered in Boston. Over the year ...

for the Army's

Chemical Corps The Chemical Corps is the branch of the United States Army tasked with defending against and using chemical, biological, radiological, and nuclear ( CBRN) weapons. The Chemical Warfare Service was established on 28 June 1918, combining activit ...

. Sweat, being partially composed of

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

, when combined with

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

produces

ammonium chloride Ammonium chloride is an inorganic chemical compound with the chemical formula , also written as . It is an ammonium salt of hydrogen chloride. It consists of ammonium cations and chloride anions . It is a white crystalline salt (chemistry), sal ...

. Chemical officers planned the detection missions, later known as Operation Snoopy, while individual Chemical Corps soldiers learned how to use the detector equipment and conduct detection operations.

XM-2

The XM-2 personnel detector manpack, also known as the E63 manpack personnel detector,Operational Report of the 9th Infantry Division for the Period Ending 31 October 1968
", November 16, 1968, p. 40, accessed October 24, 2008. was the first version of the people sniffer employed by the Army. The XM-2 featured a backpack mounted sensor with an air intake tube on the end of a rifle. The XM-2 was problematic, as it often detected the soldier carrying it rather than the enemy. The device also made a distinct sound, easily detectable by the enemy.

XM-3

The XM-3 airborne personnel detector was a helicopter mounted personnel detector and the second version of the people sniffers. The XM-3 used two independent and identical units that operated in two separate modes. In 1970, the XM-3 became the M3 personnel detector; the M3 became standard issue and was employed almost daily in LOH-6,

OH-58 The Bell OH-58 Kiowa is a family of single-engine single-rotor military helicopters used for observation, utility, and direct fire support. It was produced by the American manufacturer Bell Helicopter and is closely related to the Model 206A ...

, and

UH-1 The Bell UH-1 Iroquois (nicknamed "Huey") is a utility military helicopter designed and produced by the American aerospace company Bell Helicopter. It is the first member of the prolific Bell Huey family, Huey family, as well as the first turb ...

helicopters.Kirby, Reid.
Operation Snoopy: The Chemical Corps' "People Sniffer"
", ''

Army Chemical Review ''Army Chemical Review'' is prepared twice a year by the United States Army Chemical, Biological, Radiological, and Nuclear (CBRN) School and the Maneuver Support Center, Directorate of Training, Fort Leonard Wood, Missouri. This magazine presents ...

'', January–June 2007, pp. 20–22, accessed October 24, 2008.

Effectiveness

While useful, the detectors had to be used with some caution. People sniffers were known to be oversensitive and would often detect civilians or animals excreting bodily waste. Dunnigan, James F. and Nofi, Albert A. ''Dirty Little Secrets of the Vietnam War: Military Information You're Not Supposed to Know'',
Google Books
, Macmillan, 2000, p. 236, (), accessed October 24, 2008. In 1967 the

Army Scientific Advisory Panel The Army Science Board (ASB) provides advice about army science to senior military leaders. The ASB is a Federal Advisory Committee organized under the Federal Advisory Committee Act. It is the United States Department of the Army senior scienti ...

sent John D. Baldeschwieler to Vietnam in order to conduct controlled experiments and determine the ability of the people sniffers to detect ammonia. The tests showed that the people sniffer responded randomly to ammonia indicators, making it a very subjective instrument. Despite this, the ability of the people sniffer to detect other effluents, such as smoke, helped it to remain a valuable tool during the

. The

Viet Cong The Viet Cong (VC) was an epithet and umbrella term to refer to the communist-driven armed movement and united front organization in South Vietnam. It was formally organized as and led by the National Liberation Front of South Vietnam, and ...

(VC) and the

North Vietnamese Army The People's Army of Vietnam (PAVN), officially the Vietnam People's Army (VPA; , , ), also recognized as the Vietnamese Army (), the People's Army () or colloquially the Troops ( ), is the national Military, military force of the Vietnam, S ...

(NVA) developed effective, low-tech countermeasures to the people sniffers. The airborne sniffers soon became recognizable to the VC and NVA and they would attempt to avoid detection by not firing on Operation Snoopy missions. (Snoopy's ability to detect smoke meant it could easily locate ground troops firing with small arms, even if under cover and camouflaged.) In later Snoopy operations, the detection helicopters were disguised as gunships in order to provoke easily detectable small arms fire. Another effective decoy used by the NVA and VC involved hanging buckets of mud with urine in trees and then moving into another area. Davidson, Phillip B. ''Vietnam at War: The History: 1946–1975'',
Google Books
, Oxford University Press U.S., 1991, p. 405, (), accessed October 24, 2008. Tactics such as these essentially rendered people sniffers ineffective in jungle terrain, but they remained useful in open areas, such as those found in the

Mekong Delta The Mekong Delta ( or simply ), also known as the Western Region () or South-western region (), is the list of regions of Vietnam, region in southwestern Vietnam where the Mekong, Mekong River River delta, approaches and empties into the sea th ...

Detection method

XM-2

XM-3

Effectiveness

References

Further reading