Correspondence with Capt Basil Liddell Hart, 1954-1957, notably relating to Liddell Hart's papers for the Army League on army manpower requirements and divisional organisation. Papers relating to the Army League, 1955, 1965-1966, principally comprising draft and final copies of 'British defence policy in South East Asia', a report produced and published by the Army League, 1965; 'The Reserve Army and national security' by Maj Gen Robert Burrell Frederick Kingslake Goldsmith, published by the Army League, 1966; 'The Army in the nuclear age: report of the Army League Sub-Committee', published by the Army League, 1955.

Papers relating to his service in World War One, 1915-1918, principally comprising French and British casualty and strength figures, 1915-1918. Correspondence and associated papers relating to his work with Groupe des Armées du Nord and Grand Quartier Général, France, 1915, 1917-[1919], notably including correspondence between FM Sir Douglas Haig and Generals Robert Georges Nivelle and Henri-Philippe Pétain, 1917-1918. Operational documents, 1917-1918, mainly concerning 5 Army, IX Corps and III and VI French Armies. French Grand Quartier Général official communications, reports and telegrams, 1918, with maps relating to operations in France and Belgium, 1917-1918 and 1939-1940.

Photocopies of correspondence and photographs, taken from five albums, relating to Sclater's career, 1898-1927, including letter from FM Sir (Henry) Evelyn Wood, Adjutant General to the Forces, confirming Sclater's appointment as Bde Maj, Aldershot, 1898; seventeen copies of photographs and nine sketch maps relating to the Second Boer War, South Africa, 1899-1902, including photographs of Bloemfontein and Brandfort, Orange Free State, and sketch maps of the Battles of Modder River, Nov 1899 and Paardeberg Drift, Feb 1900; two photographs of the 13 pounder Quick Fire gun, newly issued to the Royal Horse Artillery, 1904; letter from Lt Col Rt Hon Arthur John Bigge, 1st Baron Stamfordham, thanking Sclater for congratulatory letter on the award of a peerage to Stamfordham, 1911; three photographs of Indian Army sepoys, 1912; correspondence, 1912- 1917, including letters relating to recruitment, military inspections and the availability of manpower from FM Sir John Denton Pinkstone French, Commander-in-Chief, Home Forces, Feb 1917, Gen Sir (Henry Macleod) Leslie Rundle, General Officer Commanding-in-Chief, Eastern Command, Feb-May 1916, and Lt Gen Sir (Cecil Frederick) Nevil Macready, Adjutant General to the Forces, Jul 1917; letter to Slater from Gen Sir (Francis) Reginald Wingate, relating to riots in Egypt, Jun 1920; letter to Sclater from Lt Gen Sir George Fletcher MacMunn, Quartermaster General, India, dated Jun 1921, relating to the political and military situation in India, particularly in the aftermath of the massacre of 479 Indian civilians by troops of the Indian Army, commanded by Brig Gen Reginald Edward Harry Dyer, Amritsar, Punjab, Apr 1919; printed obituary of Sclater [1927].