Question: When did the military branch employing Robert Anstruther start wearing khaki?

full_context: Document 1: Service Dress (British Army): Service Dress was the new style of khaki service dress uniform introduced by the British Army for use in the field from the early 1900s, following the experiences of a number of imperial wars and conflicts, including the Second Boer War. This variant of uniform continues to be worn today, although only in a formal role, as No. 2 Pattern dress.
Document 2: Navy blue: Navy blue got its name from the dark blue (contrasted with white) worn by officers in the British Royal Navy since 1748 and subsequently adopted by other navies around the world. When this color name, taken from the usual color of the uniforms of sailors, originally came into use in the early 19th century, it was initially called "marine blue", but the name of the color soon changed to "navy blue".
Document 3: Uniforms of the United States Navy: The Navy first authorized a khaki uniform in 1913 as a practical garment for early naval aviators; they were given permission to wear Marine Corps khaki uniforms with naval insignia, when flying or working on aircraft. Khakis were authorized aboard submarines in 1931 and as a working uniform on all ships ten years later.
Document 4: Red coat (military uniform): Red coat or Redcoat is a historical item of military clothing used widely, though not exclusively worn, by most regiments of the British Army from the 17th to the 20th centuries. From the mid-17th century to the 19th century, the uniform of most British soldiers (apart from artillery, rifles and light cavalry) included a madder red coat or coatee. From 1873 onwards, the more vivid shade of scarlet was adopted for all ranks, having previously been worn only by officers, sergeants and all ranks of some cavalry regiments.
Document 5: John Anstruther-Thomson: Colonel John Anstruther-Thomson of Charleton (15 April 1776 – 10 April 1833) was a Scottish nobleman and Colonel of the Royal Fifeshire Yeomanry Cavalry.
Document 6: Patrick Miller (politician): Patrick Miller (died 26 February 1845) was a Scottish officer in the British Army and a politician. He sat in the House of Commons of Great Britain from 1790 to 1796.
Document 7: Robert Clerk: Lieutenant-Colonel Robert Clerk (c.1720 – 1797) was a British engineer officer who served in the War of the Austrian Succession and the Seven Years' War. His report on the state of the defences of Rochefort (Rochefort, Charente-Maritime) in 1757 was the main reason for that French naval port being chosen as the target for a major British expedition, the Raid on Rochefort, for which Clerk was appointed chief engineer.
Document 8: Eton College: The long-standing claim that the present uniform was first worn as mourning for the death of George III is unfounded. "Eton dress" has undergone significant changes since its standardisation in the 19th century. Originally (along with a top-hat and walking-cane), Etonian dress was reserved for formal occasions, but boys wear it today for classes, which are referred to as "divisions", or "divs". As stated above, King's Scholars wear a black gown over the top of their tailcoats, and occasionally a surplice in Chapel. Members of the teaching staff (known as Beaks) are required to wear a form of school dress when teaching.
Document 9: United States Air Force: The first USAF dress uniform, in 1947, was dubbed and patented "Uxbridge Blue" after "Uxbridge 1683 Blue", developed at the former Bachman-Uxbridge Worsted Company. The current Service Dress Uniform, which was adopted in 1993 and standardized in 1995, consists of a three-button, pocketless coat, similar to that of a men's "sport jacket" (with silver "U.S." pins on the lapels, with a silver ring surrounding on those of enlisted members), matching trousers, and either a service cap or flight cap, all in Shade 1620, "Air Force Blue" (a darker purplish-blue). This is worn with a light blue shirt (Shade 1550) and Shade 1620 herringbone patterned necktie. Enlisted members wear sleeve insignia on both the jacket and shirt, while officers wear metal rank insignia pinned onto the coat, and Air Force Blue slide-on epaulet loops on the shirt. USAF personnel assigned to Base Honor Guard duties wear, for certain occasions, a modified version of the standard service dress uniform, but with silver trim on the sleeves and trousers, with the addition of a ceremonial belt (if necessary), wheel cap with silver trim and Hap Arnold Device, and a silver aiguillette placed on the left shoulder seam and all devices and accoutrement.
Document 10: Robert Anstruther (MP): Colonel Robert Anstruther (31 December 1757 – 1832) was a Scottish soldier in the British Army, and briefly a politician.
Document 11: Sir Alexander Don, 5th Baronet: Colonel Sir Alexander Don, 5th Baronet of Newton Don (died 1815) was a Scottish soldier who served as a British Army officer during the French Revolutionary Wars.
Document 12: British Army during the Second World War: The pre-war British Army was trained and equipped to be a small, mechanised, professional army. Its main function was to garrison the British Empire. It became evident early in the war that its initial structure and manpower was woefully unprepared and ill - equipped for a war with multiple enemies on multiple fronts. The British Army, an all - volunteer force until 1939, was small in comparison to its enemies at the start of the Second World War in 1939, as it had been in the First World War. By the end of the Second World War, however, over 3.5 million men had served in the British Army.
Document 13: Robert Lyon (politician): His father, George Lyon, was a Scottish captain in the British army, who settled in Richmond, Ontario. His oldest brother was George Byron Lyon, another mayor of Ottawa.
Document 14: Sir Robert Abercromby, 5th Baronet: Sir Robert Abercromby, 5th Baronet of Birkenbog and Forglen, FRSE (4 February 1784 – 6 July 1855) was a Scottish politician.
Document 15: Andrew Russell (New Zealand politician): Lieutenant-Colonel Andrew Hamilton Russell (1812–1900) was a British Army officer. He was appointed to the New Zealand Legislative Council from 1861 to 1872, and was Minister of Native Affairs (as the Minister of Māori Affairs was then called) from 1865 to 1866 in the Stafford Ministry.
ground_truth: early 1900s
sub_queries: Robert Anstruther >> military branch Answer: British Army
when did British Army start wearing khaki Answer: early 1900s