First World War

With the outbreak of the First World War, Barttelot initially served in France with the 4th (Reserve) Battalion Coldstream Guards, from 12 August 1914, where he was wounded at the Battle of the Aisne and also awarded the French Croix de Guerre.^[4][17] He was then appointed a General Staff Officer, Grade III on 11 February 1915 and was concerned with coastal defence around Portland,^[4][18] and served in the ill-fated Gallipoli campaign from July 1915,^[4][19] where he was promoted major on 1 September 1915.^[20] He was appointed a brigade major on 11 January 1916,^[21] for the Mesopotamian campaign. He was appointed to the Distinguished Service Order (DSO) on 22 December 1916,^[22] and appointed GSO, Grade II from 11 September 1917.^[23] and was Military Attaché to Tehran from 17 March 1918 with temporary promotion to lieutenant-colonel whilst performing those duties.^[24] He was awarded a brevet promotion to lieutenant-colonel for his service in Mesopotamia on 3 June 1918,^[25] and was killed, (aged 38) on 23 October 1918 in Tehran, Persia^[4] and was buried in the Tehran War Cemetery.^[26][27] In addition to his DSO, he had also been Mentioned in Despatches four times.^[27]

He had come to know Gertrude Bell during his time in Tehran, and in a letter to her mother on 25 October 1918, she wrote:

A terrible tragedy has happened at Tehran [(Teheran)]. I think I must have written to you about the Military Attach‚, Sir Walter Barttelot, with whom I used to ride at Gulhak before breakfast. He was also our host on the night expedition into the hills which I described to you. He has been murdered in his bed by a jealous husband - I know no details but I profoundly believe that there was nothing in the whole business but wicked Tehran gossip. The wife in question, Mrs Maclaren, left Tehran a month ago and passed through here on her way to England. I didn't see her in Baghdad, partly because I was having influenza at the time and other partly because, though I had seen very little of her at Gulhak, I thought her Class B lady and had no special wish to renew the acquaintance. Also she had quarrelled with the Marlings, the wrong quite on her side, as far as I could see, and I didn't want to be mixed up in any dissensions. It's a truly shocking business. Sir Walter had a wife in England and a boy at Eton, about both of whom he used to talk to me continuously. He was a nice, pleasant, not particularly brilliant British landowner; we made rather friends, just because he was the sort of man I knew at home - at least that was my feeling about him. He was not well suited in his Tehran job and was longing to get away. I told the C.G.S. this when I came back, a successor was found for him, and he would have probably have been back in England before the end of the year. Oh dear, I'm so sorry for his wife and boy. Maclaren I thought a dreadful man - class W, if not Z. He is a consul.^[28]