He served in several regiments, and commanded a battalion of the Imperial Yeomanry, the 10th (Prince of Wales's Own) Royal Hussars, the 111th Brigade, and three divisions.

He was educated at Westminster School, before in December 1888, becoming a second-lieutenant in the part-time 4th (Hereford Militia) Battalion, King's Shropshire Light Infantry.

[5] In 1894 and again in 1895 Barnes was one of a cabal of subalterns who harassed fellow junior officers into leaving the regiment because they were perceived as not meeting its social or other standards.

But both officers were also under orders from Colonel Edward Chapman, the British Director of Military Intelligence to "collect information and statistics on various points and particularly as to the effect of the new bullet its penetration and striking power".

[14] Only two months later, in July 1901,[15] he was promoted to temporary lieutenant-colonel and commanding officer of the 2nd Battalion Imperial Yeomanry, serving as such until March 1902,[16] when he returned to an ordinary posting in his regiment.

[21] He remained with his new regiment until October 1909 and was the employed by as the Assistant Military Secretary to the Governor and Commander-in-Chief, Malta Leslie Rundle.

[26] They then travelled to the Western Front as part of the 3rd Cavalry Division, commanded by Major General Sir Julian Byng, missing the early stages of the conflict.

[34] His promotion to substantive major-general came in May 1918;[35] and he took command of the Territorial Force's 57th (2nd West Lancashire) Division from 1 July 1917 to the end of the war.

[40] Away from army life he resided at Oakhay Barton, Stoke Canon in Devon, marrying Gunhilla Wijk, a widow, in 1919.