Career
During World War I Colquhoun served in the Scots Guards and by 1918 he was Commanding Officer of 2/4th Battalion, Leicestershire Regiment in 59th (2nd North Midland) Division. When the German Spring Offensive opened on 21 March 1918, the division"s forward defences were quickly overrun. 2/4th Leicesters had only just come out of the line after 24 hours of continuous trench duty, but were sent straight back up to assist in the defence.
The battalion could get no further forward than the rear of the Battle Zone where the "line" was no more than a yet-to-be-dug trench marked out with the turf removed and no barbed wire.
The men extended along the line even though they were completely exposed in the open. Under the inspiring leadership of Lieutenant-Colonel Colquhoun and Regimental Sergeant-Major "African Joe" Withers, the battalion held off the Germans for the rest of the day, with modest casualties.
After the war he was Honorary Colonel of the 9th Battalion Argyll and Sutherland Highlanders and Glasgow University Officer Training Corps, and President of the Dunbartonshire Territorial Association. He succeeded his father as the 7th Baronet in 1910, as Sir Iain Colquhoun of Luss, and Chief of the Clan Colquhoun.
He was created a Knight of the Thistle in 1937.
He was elected a Fellow of the Royal Society of Edinburgh in 1938.
