25 years ago:

11–20 May 1996     In Iraq, UNSCOM conducts its 35th biological-weapons inspection, UNSCOM 145. The mission is both for purposes of the ongoing monitoring and verification system and for sampling in connection with the past Iraqi BW programme.[1]
     [1] Report of the Secretary-General on the Activities of the Special Commission Established by the Secretary-General Pursuant to paragraph 9(b)(1) of Resolution 687 (1991), as annexed to UN document S/1996/848, 11 October 1996.

35 years ago:

25 May 1986     Iran accuses Iraq of deploying chemical bombs twice this day in Mehran and Saleh-Abad region in the west of Iran. IRNA is quoted as saying "the casualty is not high as the Iranian forces were equipped with antichemical gas masks".[1]
     Two days later foreign journalists are taken by Iranian officials to the Labbafi Nejad Hospital in Tehran. Journalists report that they meet Iranian soldiers said to have been injured "in the air raid near the city of Mahran". The head of the hospital tells the journalists that the soldiers had been exposed to mustard gas and that 6 of the 38 Iranian soldiers brought to the hospital following the attack are in critical condition. Hospital authorities say that the hospital has treated some 500 people injured by chemical weapons since February.[2]
     [1] [No author listed] (from Tehran), "Iran Bombs Military, Economic Targets in Iraq", Xinhua General Overseas News Service, 26 May 1986, ref 0526009.
     [2] [No author listed] (from Tehran), "Iran Accuses Iraq of Chemical Bombing", Xinhua General Overseas News Service, 28 May 1986, ref 0528019.

45 years ago:

4 May 1976     Switzerland deposits its instrument of ratification to the Biological Weapons Convention in London, Moscow and Washington, having signed the Convention on the day it was opened for signature [see 10 April 1972]. The deposit was accompanied with the following statement: "1. Owing to the fact that the Convention also applies to weapons, equipment or means of delivery designed to use such biological agents or toxins, the delimitation of its scope of application can cause difficulties since there are scarcely any weapons, equipment or means of delivery peculiar to such use; therefore, Switzerland reserves the right to decide for itself what auxiliary means fall within that definition.
     "2. By reason of the obligations resulting from its status as a perpetually neutral State, Switzerland is bound to make the general reservation that its collaboration within the framework of this Convention cannot go beyond the terms prescribed by that status. This reservation refers especially to Article VII of the Convention as well as to any similar clause that could replace or supplement that provision of the Convention (or any other arrangement)."
     [Note: this statement is the same as the last two paragraphs of the statement made by Switzerland on signature to the BWC and which provoked a response by the United States, see 4 October 1973.]

65 years ago:

30 May 1956     The freighter Vogtland is scuttled with a cargo that includes chemical munitions being disposed of by the United Kingdom. The location is given as 56 30.00N, 12 00.00W at a depth of 2500 metres.[1] This is the second scuttling under Operation Sandcastle [see 27 July 1955].
     [1] UK Ministry of Defence, "British Isles Explosive Dumping Grounds", August 2005, available via http://www.mod.uk.

70 years ago:

8 May 1951     Pyongyang sends `a vigorous protest to the United Nations against a further monstrous crime which is being committed by the American interventionists by the use of bacteriological weapons in the war against the Korean people'. This protest is contained within a cablegram sent from the Minister for Foreign Affairs, Pak Hen En, addressed to the President of the Security Council.[1]
     The cablegram goes on to allege that the staff of former US Commander MacArthur "spent one and a half million yen on the preparation of bacteriological weapons, using the Japanese Government as agents for the placing of orders", suggesting that this particular allegation had been reported in the press. The cablegram further suggests that "documents of the secret archives of the Syngman Rhee Government captured in the liberation of Seoul" should that it had prepared for the use of "secret bacteriological warfare against the North". The cable alleges that recent outbreaks of smallpox were the result of "the premeditated crime of the American interventionists, perpetrated in violation of the Geneva Protocol ... to which the United States is a signatory".
     [1] Korean People's Democratic Republic, Cablegram dated 8 May 1951 from the Minister for Foreign Affairs of the Korean People's Democratic Republic addressed to the President of the Securiy Council, as reproduced in S/2142/Rev.1, dated 18 May 1951.