troops. After Iran sent chemical casualties to several Western nations for treatment, the UN dispatched a team of specialists to the area in 1984, and again in 1986 and 1987, to verify the claims. The conclusion from all three trips was the same: Iraq was using chemical weapons against Iranian troops and civilians. In addition, the second mission stressed that Iraq's use of chemical weapons appeared to be increasing. The reports indicated that mustard gas and tabun were the primary agents used and that they were generally delivered in bombs dropped by an airplane. The third mission (the only one allowed to enter Iraq) also reported the use of artillery shells and chemical rockets and the use of chemical weapons against civilian personnel. In the letter of transmittal to the UN after the conclusion of the third mission, the investigators pointed out the dangers of this chemical warfare: It is vital to realize that the continued use of chemical weapons in the present conflict increases the risk of their use in future conflicts. In view of this, and as individuals who witnessed first hand the terrible effects of chemical weapons, we again make a special plea to you to try to do everything in your power to stop the use of such weapons in the Iran–Iraq conflict and thus ensure that they are not used in future conflicts. ... In our view, only concerted efforts at the political level can be effective in ensuring that all the signatories of the Geneva Protocol of 1925 abide by their obligations. Otherwise, if the Protocol is irreparably weakened after 60 years of general international respect, this may lead, in the future, to the world facing the specter of the threat of biological weapons. Declassified documents later revealed that the United States was both aware of Iraq's use of chemical weapons, and also facilitated its acquisition of chemical and biological precursors which were used to make weapons. Another analyst insisted that "In a sense, a taboo has been broken, thus making it easier for future combatants to find justification for chemical warfare, this aspect of the Iran–Iraq War should cause Western military planners the gravest concern." The Iran–Iraq War failed to reach a military conclusion despite Iraq's use of chemical weapons. Roughly 5% of the Iranian casualties were caused by chemical weapons. The toll may surpass 90,000 though, according to Iranian experts, since the