35 years ago:

6 May 1987     The UN Secretary-General receives the report of the mission he had sent to both Iraq and Iran to investigate the complaints of chemical weapons which each had lodged against the other.[1] The report confirms the use by Iraq of CW agents against Iranian civilians as well as soldiers and that Iraqi military personnel, too, had displayed injuries caused by CW agents, but the evidence regarding the source of those injuries was inconclusive.
     In their letter of transmittal, the team members recount: "Although the number of chemical casualties we saw in the Islamic Republic of Iran and the severity of their injuries was considerably less than seen by us in 1986, we were very disturbed to find that there now have been numerous civilian casualties as a result of attacks by mustard gas. In a hospital in Tehran we saw the effects of mustard gas on a peasant family, particularly a mother and her two small daughters aged two and four years. We had the distressing experience of witnessing the suffering of the four-year-old child less than two hours before her death. In addition, we saw the very damaging effects of mustard gas on the young mother, who was four months pregnant".
     Pleading for everything possible to be done to stop the use of chemical weapons in the war, the experts note: "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". They also note that the team members have now conducted three missions to the Islamic Republic of Iran and one to Iraq and: "We all firmly believe that, at the specialist level, we have done all that we can to identify the types of chemicals and chemical weapons being used in the Iran–Iraq conflict. If, in the future, a further mission is requested, then we will of course all be ready to respond. However, we now feel that technically there is little more that we can do that is likely to assist the United Nations in its efforts to prevent the use of chemical weapons in the present conflict".
     The report of the investigation team concludes: "(a) There has been repeated use of chemical weapons against Iranian forces by Iraqi forces, employing aerial bombs and very probably rockets. The chemical agents used are mustard gas (yperite) and probably, on some occasions, nerve agents; (b) A new dimension is that civilians in Iran also have been injured by chemical weapons; (c) Iraqi military personnel have sustained injuries from chemical warfare agents, which are mustard gas (yperite) and a pulmonary irritant, possibly phosgene".
     The report is circulated to the members of the Council on 8 May and published on 13 May.
     [Note: rumours circulate that this investigation mission encountered Iraqi Kurds suffering from injuries caused by attacks by Iraqi armed forces using chemical weapons, but this was considered to be outside the remit of the team to include in this report. However, the information is said to have been conveyed to the office of the Secretary-General by other means.]
     [1] Report of the mission dispatched by the Secretary-General to investigate allegations of the use of chemical weapons in the conflict between the Islamic Repiublic of Iran and Iraq, UN document S/18852, 8 May 1987 and Corr.1, 26 May 1987; and, as an Addendum, "Appendix III. Summary report on patients examined by the medical specialist...", UN doc S/18852/Add.1, 18 May 1987.

45 years ago:

May 1977     In the United Kingdom the final transport of nerve agent from the Ministry of Defence production establishment at Nancekuke to Porton Down takes place. The quantity concerned is said to be small and the Government states that "appropriate precautions were taken to ensure that there was no hazard to the public". [1]
     [1] Jeremy Hanley, Minister of State for the Armed Forces, Written Answer, 19 July 1993, Hansard (Commons), vol 229, col 80–83, including a letter from Graham Pearson, Chief Executive, Chemical and Biological Defence Establishment.

50 years ago:

11 May 1972     Iraq signs the Biological Weapons Convention — which had been open for signing by all states of the world since 10 April — registering its signature with the Soviet Union, one of the three depositaries of the treaty. A key obligation within this convention is contained in Article I: "Each State Party to this Convention undertakes never in any circumstance to develop, produce, stockpile or otherwise acquire or retain: (1) Microbial or other biological agents, or toxins whatever their origin or method of production, of types and in quantities that have no justification for prophylactic, protective or other peaceful purposes; (2)Weapons, equipment or means of delivery designed to use such agents or toxins for hostile purposes or in armed conflict". Iraq's signature remains unratified for 19 years.

70 years ago:

28 May 1952     US President Harry S. Truman states "The Kremlin cries that we have used germ warfare. There isn't a word of truth in that. We have never broken the Geneva Convention [sic] in our operations in Korea. And they know that. They know it well. But they keep on passing out the lies that have no foundation in fact whatever".[1]
     [1] President Truman, Remarks to Members of the American Action Committee Against Mass Deportations in Romania, 28 May 1952, as cited by the American Presidency Project, at http://www.presidency.ucsb.edu/ws/?pid=14134.

75 years ago:

6 May 1947     US General Douglas MacArthur sends a message to Washington DC on the continuing investigations into the Japanese biological warfare programme.[1] The message includes: "Experiments on humans were known to and described by three Japanese and confirmed tacitly by Ishii ... Ishii states that if guaranteed immunity from "war crimes" in documentary form for himself, superiors and subordinates, he can describe program in detail. Ishii claims to have extensive theoretical high-level knowledge including strategic and tactical use of BW on defense and offense, backed by some research on best BW agents to employ by geographical areas of Far East and the use of BW in cold climates".
     Part 3B of the message states: "Additional data, possibly including some statements from Ishii, probably can be obtained by informing Japanese involved that information will be retained in intelligence channels and will not be employed as "war crimes" evidence" and Part 5 states "Adoption of method in Part 3B above recommended ... . Request reply soonest".
     The same day, a government cable is sent from Washington DC to US officials in Japan: "Recommendation approved. Information obtained from Ishii and associates on biological warfare will be retained in intelligence channels and will not be employed as "war crimes" evidence".[2] This cable is revealed in a television programme some decades later which cites it as evidence of official US connivance in a post-war cover-up of the Japanese BW programme, including Unit 731.
     [1] As quoted in: Peter Williams and David Wallace, Unit 731: the Japanese Army's secret of secrets, London: Hodder and Stoughton, 1989, pp 194–95, citing the source as "Radio C-52423, CnC FE, Tokyo, Japan, to War Department for WDGID (pass to CCMLC) MID pass to Maj-Gen Alden Waitt, May 6, 1947". Parts of the message are also reproduced in: Robert Harris and Jeremy Paxman, A Higher Form of Killing: the secret history of chemical and biological warfare, (1st edition), London: Chatto & Windus, 1982, p 153.
     [2] As quoted in: Sara James (reporter), "Factory of Death", television documentary on NBC News Dateline, 15 August 1995, as transcribed by Burrelle's Information Services.