It has been alleged that the British used chemical weapons in Mesopotamia in 1920, during the Iraqi revolt (Ath Thawra al Iraqiyya al Kubra), in the period of the British Mandate over Mesopotamia. Use of tear gas and lethal poison gas against Iraqi rebels was considered, and the use of gas was promoted by Winston Churchill, head of the War Office, who encouraged research into the dropping of mustard gas by air. Tear gas artillery shells were transported to Iraq and approval was given for their use, but tests by the army found them to be impractical and they were not used in combat. Efforts to develop gas weapons for use in Iraq were halted by the British over concerns about embarrassing political repercussions following the signing of the Washington Disarmament Treaty, which contained a provision outlawing poison gas, although the British government held that the use of tear gas remained legally permissible. Practical difficulties ultimately prevented the use of gas, rather than any moral inhibitions. Historiography Historian Charles Townshend made the "first assertion of British chemical weapons use in Iraq" in his 1986 essay Civilisation and "Frightfulness": Air Control in the Middle East Between the Wars: Britain was not a free agent in the middle east, and would have to defer to the universal prejudice against all forms of gas. In vain did the Air Ministry stress that lethal concentrations were most unlikely to be reached under air bombardment (because - though this point was not stressed - of its low accuracy). In vain did they point out that the army had used SK gas shells in quantity against the Mesopotamian rebels in 1920 with 'excellent moral effect'. In his book World Orders Old and New, Noam Chomsky claimed that Churchill was particularly keen on chemical weapons, suggesting they be used "against recalcitrant Arabs as an experiment". Churchill dismissed objections to the use of chemical weapons as "unreasonable" and stated: "I am strongly in favour of using poisoned gas against uncivilised tribes". In March and July 1992, US Representative Henry B. González, speaking in the House of Representatives, claimed that Britain used chemical weapons during the Iraqi–Kurdish conflict. Criticism of allegations The main source usually quoted in support of the idea that Britain used poison gas in Mesopotamia is Geoff Simons, Iraq: From Sumer to Saddam (1994), who stated that "gas was used against the Iraqi rebels in 1920".