Major General Sir Henry Fleetwood Thuillier, KCB, CMG (30 March 1868 – 11 June 1953) was a British Army officer who played a significant part in the development of gas warfare.

Thuillier was born at Meerut, Uttar Pradesh, India, on 30 March 1868, the son of Colonel Sir Henry Ravenshaw Thuillier.^[1]

Thuillier was commissioned into the Royal Engineers on 23 July 1890.^[2] His early career was spent in India.^[1]

He became commander of 2nd Infantry Brigade in October 1915, General Officer Commanding 15th (Scottish) Division in June 1917, after receiving a temporary promotion to major general,^[3] and General Officer Commanding 23rd Division in Italy in 1918, during the First World War.^[4]

After the war Thuillier, promoted in June 1919 to substantive major general,^[5] became Commandant of the School of Military Engineering in November 1919, Director of Fortifications and Works at the War Office in 1924,^[6] and General Officer Commanding 52nd (Lowland) Infantry Division in June 1927. He retired from the army in March 1930.^[7] He died on 11 June 1953.^[1]

• The Principles of Land Defence and Their Application to the Conditions of To-Day. 1902.
• Gas in the next war. Geoffrey Bles, London, 1939. (German translation published in Zürich by Scientia, 1939, as Das gas im nächsten krieg. Introduction and notes by V. Tempelhoff).

Thuillier's son was Lieutenant Colonel Henry Shakespear Thuillier.^{[8][self-published source]}

• Leslie de Malapert Thuillier

• Correspondence at the National Archives