. At the outbreak of the Second World War Dill hoped to be appointed Commander-in-Chief of the British Expeditionary Force, but the position again went to Gort. The resulting vacancy as Chief of the Imperial General Staff (CIGS) was filled by Sir
Edmund Ironside, leaving Dill to be eventually posted as commander of
I Corps in France on 3 September 1939. He was promoted to
general on 1 October 1939 (with seniority backdated to 5 December 1937). Dill was appointed
Vice Chief of the Imperial General Staff (and a member of the
Army Council), under Ironside, by the then Prime Minister
Neville Chamberlain. On 27 May 1940, after Chamberlain had been replaced by Churchill, Dill replaced Ironside as CIGS. and
Edward Puttick, Major-General
Bernard Freyberg and General Dill, Brigadiers
James Hargest and
Harold Barrowclough. Faced with the prospect of a
German invasion, Dill produced a memorandum on 15 June advocating the use of chemical warfare against an enemy landing. Although acknowledging that first use of chemical weapons would alienate the United States and invite retaliation, he concluded that "at a time when our National existence is at stake ... we should not hesitate to adopt whatever means appear to offer the best chance of success." After criticism from the Director of Home Defence and other offices Dill withdrew the memorandum. Nevertheless, the proposal was largely endorsed by Churchill on 30 June and it was ordered that the
Royal Air Force begin preparations for deploying
mustard gas, although he added that actual employment would need to be ordered by the
Cabinet. and posted him to
Washington, D.C. as his personal representative where he became Chief of the
British Joint Staff Mission, then Senior British Representative on the Combined Chiefs of Staff. Dill showed a great flair as a diplomatic military presence. In 1943 alone he attended the
Quebec Conference, the
Casablanca Conference, the
Tehran Conference and meetings in India, China and Brazil. He also served on the
Combined Policy Committee set up by the British and United States governments under the
Quebec Agreement to oversee the construction of the
atomic bomb. He was awarded the
Howland Memorial Prize in 1944, in part to ensure his continued favour with Churchill. In the United States he was immensely important in making the Chiefs of Staff committee – which included members from both countries – function, often promoting unity of action. He was particularly friendly with General
George Marshall and the two exercised a great deal of influence on President
Franklin Delano Roosevelt who described Dill as "the most important figure in the remarkable accord which has been developed in the combined operations of our two countries". ==Death==