Insurgents detonated three vehicle-borne improvised explosive devices (VBIEDs) packed with chlorine in Iraq's Anbar province west of Baghdad on March 16. The initial blasts, which U.S. officials blamed on al Qaeda in Iraq, killed at least six people, while at least 350 Iraqi civilians and six U.S. troops fell ill as a result of chlorine exposure. Although the deaths were caused by the blasts rather than the chlorine — as in similar attacks involving chlorine bombs earlier in the year — these latest attacks clearly demonstrate al Qaeda's fascination with combining chlorine and explosives to create crude chemical weapons. Causing mass casualties with chemical VBIEDs is extremely difficult, though the fear incited by such attacks makes these kinds of bombs increasingly popular among insurgents. Moreover, as the insurgents gain experience with the devices — and increase their lethality — the tactic likely will spread beyond Iraq. Chlorine bombs are relatively easy weapons for the Iraqi insurgents to make. The devices used in the latest attacks involved a pickup truck and two dump trucks loaded with chlorine tanks and rigged with explosives. One of the dump trucks reportedly carried a 200-gallon chlorine tank. One truck detonated at a checkpoint near Ar Ramadi, while another killed two Iraqi policemen in Al Amiriyah. The most devastating attack occurred three miles south of Al Fallujah when a dump truck targeted the reception center of a tribal sheikh who had denounced al Qaeda. The use of chlorine in chemical VBIEDs is attractive to militants because the chemical is widely available in Iraq and around the world. The problem, as Iraqi militants are finding, however, is dispersing the chemical with a VBIED while maintaining an effective concentration of the gas. As a result, the chlorine bombs seen to date in Iraq have been tremendously ineffective in inflicting mass casualties, especially when compared with traditional car bombs, which do kill large numbers of people when detonated in populous areas. Regardless of these bombs' effectiveness as mass killers, however, insurgents like them because the immediate chlorine odor incites fear. Witnesses of the Iraqi attacks, for example, reported nasty smells and a white plume of smoke that turned black and blue. Furthermore, these attacks are valuable to insurgents as tests for future operations elsewhere. Whether this method of attack is the fixation of a particular insurgent leader or it represents an emerging doctrine by al Qaeda in Iraq, the attacks will allow the insurgents to gain tactical expertise and learn to construct more effective chemical bombs. The attackers also could be conducting these attacks to gauge security weaknesses or to divert attention from a different location where an operation is planned. Chemical VBIED attacks are likely to continue in Iraq and to spread as those responsible for them export the knowledge gained throughout the region and beyond. Al Qaeda units in other locations followed the lead of al Qaeda in Iraq as it increased its use of tactics such as employing roadside bombs and conducting beheadings — and the use of chlorine bombs could be next. The Iraqi insurgency has proven to be an effective training ground for foreign jihadists, much as the Afghan resistance was two decades earlier. Al Qaeda sprang from the Afghan conflict, and today foreigners from Saudi Arabia, Syria, North Africa and elsewhere are honing their insurgent skills on the battlegrounds of Iraq — and are then returning home to spread jihadist tactics. This has been seen most recently in the Maghreb, where the regional al Qaeda arm is increasingly employing improvised explosive devices in attacks, especially against foreign energy workers. Because chlorine is so common, movement of the chemical cannot be severely restricted. This is especially true in areas where the state already has a weak hold on the security situation. Therefore, Iraqi insurgents are likely to continue refining their technique — and their allies and sympathizers beyond the state will start to adopt the tactic themselves.