In the third edition of his book, Iraq: From Sumer to post-Saddam (2004), Simons wrote: "In the event, gas was used against the Iraqi rebels in 1920 with "excellent moral effect", though gas shells were not dropped from aircraft because of practical difficulties". Another historian, Lawrence James, stated, "By September the local commander, General Sir Aylmer Haldane, was beginning to get the upper hand, although he was still desperate enough to clamour for large supplies of poison gas. It was not needed, for air power had given his forces the edge whenever the going got tough". On whether gas was used he writes that: "RAF Officers asked Churchill... for use of poison gas. He agreed but it was not used". Niall Ferguson, in his 2006 book The War of the World, wrote: "To end the Iraqi Insurgency of 1920... the British relied on a combination of aerial bombardment and punitive village burning expeditions. Indeed, they even contemplated using mustard gas too, though supplies proved unavailable". Anthony Clayton wrote in The Oxford History of the British Empire that "the use of poisonous gas was never sanctioned". A December 2009 article in the Journal of Modern History by R. M. Douglas of Colgate University went through the surviving documentary sources and concluded that "while at various moments tear gas munitions were available in Mesopotamia, circumstances seeming to call for their use existed, and official sanction to employ them had been received, at no time during the period of the mandate did all three of these conditions apply" and that it was clear that no poison gas was used. Douglas noted that Churchill authorised a shipment of artillery shells containing ethyl iodoacetate, a tear gas, from Egypt to Iraq on 17 September 1920 for use by the army, but after trials on British soldiers the large quantity of shells needed to produce a significant irritant effect was found to be logistically impractical. The air force remained enthusiastic about the use of gas, and on 9 January 1922 Churchill approved the conversion of gas artillery shells for use from aircraft. However, this plan was halted by Churchill on 31 January under pressure from the Air Council as the Washington Disarmament Treaty, signed on 7 January at the Washington Naval Conference, had included a provision (article 5) prohibiting the use of "asphyxiating, poisonous or other gases". The War Office also instructed the Mesopotamian Expeditionary Force