Is the XM1063 a stink bomb, a banana skin, or a bad trip? It's hard to know. XM1063 is the code name for the US army's new secret weapon which will "suppress" people without harming them, as well as stopping vehicles in an area 100m square. But is it a violation of chemical weapons treaties, or a welcome move towards less destructive warfare using non-lethal weapons?

Exactly how it works is classified, but we have established some details. The first part of the weapon is an artillery round - or as the army puts it, "a non-lethal personal suppression projectile" - fired from a 155mm howitzer, with a range of 28km. It scatters 152 small non-explosive submunitions over a 1-hectare area; as each parachutes down, it sprays a chemical agent. Development was overseen by the US Army's Armament Research, Development and Engineering Centre (Ardec).

A presentation by the makers, General Dynamics, says the XM1063 will "suppress, disperse or engage personnel" and "deny personnel access to, use of, or movement through a particular area, point or facility" (=see PDF).

Smelling it out

Experts suggest three possible payloads: an existing riot-control agent, malodorants or a new chemical agent. Existing agents include CS gas and a form of pepper spray. But these seem unlikely choices, because their effects only last minutes, and could wear off before friendly forces arrive. They could also face a legal challenge: the 1997 Chemical Weapons Convention prohibits the use of riot control agents in warfare

"The matter is further complicated if pepper gas was used as the irritant since this is a plant toxin," says Steve Wright of Leeds Metropolitan University. "Such toxins are explicitly banned."

The possibilities seem to boil down to anti-traction agents (which make the whole area impossibly slippery), a malodorant or some novel chemical agents.

Anti-traction agents are possible, but seem unlikely because research in this area (such as Darpa's Black Ice program) still seems to be at an early stage. It would be unusual for an agency to still be doing basic research when another is about to field a finished product.

A malodorant is a super stinkbomb with a truly intolerable smell. The Pentagon has been working on such chemicals for years, and a recent US army briefing on future artillery concepts specifically mentions artillery-delivered malodorants. (see PDF)

This might sidestep the Chemical Weapons Convention with the argument that malodorants are not chemical weapons. However, Ralf Trapp, an independent disarmament consultant formerly with the Organisation for the Prohibition of Chemical Weapons, challenges this interpretation.

"That argument rests on the assumption that there are no other toxic effects of these chemicals, and that one can control the dose so that one never crosses into the dose range for toxic effects," says Trapp. "It also is based a concept of toxicity that is centuries out of date - malodorants do have a physiological effect and toxicity is not limited to lethality."

Finally, there is the possibility that the US has decided to ignore the convention and use new non-lethal chemical agents. This approach has supporters in high places. Before the Iraq war in 2003, Donald Rumsfeld pushed for rules of engagement that would allow US forces to use non-lethal chemicals.

Until the 1980s, the US maintained stockpiles of a chemical incapacitant known as BZ or Agent Buzz. BZ is a psychoactive chemical causing stupor, confusion and hallucinations lasting for more than 24 hours. It has an evil reputation, but this is based largely on rumour as few facts are available. Most people have only heard of BZ in connection with the film Jacob's Ladder. This depicted soldiers exposed to a secret chemical weapon in Vietnam with terrible results, including permanent psychosis.

"We are reaping the whirlwind today because of government secrecy in the past," says Jim Ketchum, who ran the BZ testing program in the 1960s. "It has allowed critics to make unsupportable claims about agents such as BZ without rejoinder from the government research community." Although the US is known to have been active in this area since 2000, no comments are available from researchers on non-lethal chemical agents - now termed "calmatives", whatever their chemical action.

Ketchum has written a book, Chemical Warfare Secrets Almost Forgotten, about his experiences of testing BZ on hundreds of volunteers. The effects are very different to those portrayed by Hollywood. None suffered physical harm, mental breakdown or any lasting after-effects. Rather than driving subjects berserk, it has a sedative action. But unlike the fentanyl used in 2002 by Russian police when they stormed a Moscow theatre where Chechen rebels were holding hostages, BZ does not rely on sedation for its effects and does not carry the same risk.

Clouding the issue

Ketchum is now retired, and his successors have had decades to develop more effective and safer agents. But strict secrecy is still in place and there is no information about current research. Ketchum argues that the use of incapacitants would save lives, especially in situations where insurgents are mixed with the civilian population. Others believe that such agents are not just illegal but a step towards unlimited chemical weapons.

"It shouldn't be forgotten that the horrors of gas warfare in the first world war began with teargas, followed up with lethal firepower," says Wright.

As a sideline, the XM1063 projectile also has a "vehicle area denial" component composed of nanoparticles. The US army has researched chemicals to interefere with engine combustion in the past, including work with ferrocene (normally used as an anti-knock additive) which prevent engines from working, with the idea is that this would stop any vehicle within the affected area. However, the potential health risks are unknown, especially when nanoparticles are involved.

Testing of the XM1063 was completed successfully last year and it is due for low-rate production from 2009. Ardec says that the production decision is on hold awaiting further direction from the program manager. It seems the decision on whether to enter a new age of chemical warfare now rests with the military rather then civilians. Unless put under pressure, the US Army seems unlikely to give any details of what's in the surprise package until it is used. And maybe not even then.