A second invasion of Iraq may soon be under way — this time by military teams of technical experts trained to identify and destroy weapons of mass destruction (WMD).

According to the US Department of Defense, 'assessment teams' will examine a prioritized list of suspected WMD sites. Where they find suggestions of suspicious activity, 'mobile exploitation teams' will be called in to take samples and conduct further analyses in sophisticated mobile laboratories. Finally, 'disablement teams' will be deployed to destroy any biological or chemical weapons that are found.

The Pentagon declines to comment in detail on the technology at the teams' disposal. But the assessment teams are likely to be equipped with portable devices that can rapidly scan for the presence of banned weapons. These include hand-held chemical-agent monitors, which ionize air samples and then examine the mobility of the clusters of ions that are formed. Another portable device can analyse chemicals inside sealed containers by recording the γ-ray spectrum given off when the contents are bombarded with neutrons.

But experts warn that portable devices — which may also be carried by frontline troops — can give false positive results. This happened several times during the first Gulf War, says Kenneth Boutin, a researcher at VERTIC, a non-governmental organization in London interested in the verification of arms-control agreements. As Nature went to press, the dubious reliability of initial reports had already been underlined by a claim on 23 March — later dismissed as “premature” by Pentagon sources — that US troops had found a chemical-weapons facility near Najaf, some 160 kilometres south of Baghdad.

The Pentagon says that its teams may seek help from members of the United Nations Monitoring, Verification and Inspection Commission (UNMOVIC), the inspection body that until recently was operating in Iraq. “We envisage, at the appropriate time, augmenting our teams in theatre with former UN inspectors,” a Pentagon spokesman told Nature. According to some reports, several UNMOVIC inspectors have already been approached.

But given that the political justification for the war depends heavily on the assertion that Iraq has continued to possess WMDs in defiance of UN resolutions, the international community may want to see verification of any positive results by laboratories entirely independent of the US and British governments. “Independent verification is vital,” says Julian Perry Robinson of the University of Sussex in Brighton, director of the Harvard Sussex Program, which aims to inform public policy on chemical and biological warfare.