The papers cover the period, 1879-1916, and include papers on Howell's service as a correspondent for The Times in the Balkans, including photographs and newspaper cuttings, 1903; papers on Howell's training at Staff College, Quetta, India, and Staff College, Camberley, Surrey, including notes on Cavalry organization and tactics and on the establishment of Frontier Intelligence organization in India, 1904-1914; papers on service as Officer Commanding 4 Hussars, including Operational orders, accounts of Allied operations on Western Front, personal diaries and manuscript maps of Western Front trenches, 1914-1915; Operational orders from service as Brig Gen, General Staff Cavalry Corps, Western Front, 1915; official and semi-official correspondence from service as Chief of Staff, Salonika, including personal diaries, correspondence relating to attempts to secure Bulgarian entry in World War One on the Allied side, and correspondence relating to allegations of Howell leaking memoranda to a Suffragete newspaper called Britannia, 1915-1916. The collection also includes Howell family correspondence, 1879-1889, mostly between Howell's father and grandfather, and from 1909-16 between Howell and his wife Mrs Rosalind 'Linnett' Howell [nee Buxton].

The papers of Howell's wife, Mrs Rosalind 'Linnett' Howell [nee Buxton], 1910-1966, include an account of Howell's life entitled, Philip Howell. A Memoir By His Wife (1942, London, George Allen & Unwin Ltd) and letters from Capt (Edward) Hugh Buxton and Maj (Abbot) Redmond Buxton [Rosalind 'Linnett' Howell's brothers], concerning Allied withdrawal from Anzac Cove and Sulva Bay, Gallipoli, Turkey, 1915-1916.

Papers, 1814-2015, relating to Hamilton's life, military career and activities. The collection specifically includes correspondence, 1852-1899; diaries and notebooks, 1870-1899; printed correspondence and speeches of FM Frederick Sleigh Roberts, 1st Earl Roberts of Kandahar, Waterford and Pretoria, 1878-1893; diaries kept during the siege of Ladysmith, South Africa, 1899-1900; personal and official correspondence during the Second Boer War, 1899-1902, including Hamilton's letters to FM Frederick Sleigh Roberts, 1st Earl Roberts of Kandahar, Waterford and Pretoria, 1901-1902, and operational correspondence of 10 Div and Hamilton's Force, 1900; Hamilton's diaries of the Russo-Japanese War, 1904-1905 and related correspondence, 1902-1905; publications of the Royal Commissions on the war in South Africa and on the Militia and Volunteers, 1903-1904; correspondence as General Officer Commanding Southern Command, 1905-1909, and related official papers; correspondence as General Officer Commanding Mediterranean Command and Inspector General of Overseas Forces, 1910-1914, including papers relating to compulsory and voluntary military service, official reports on overseas forces, and correspondence relating to Hamilton's tours of the West Indies, South Africa, the Far East, Canada, Australia and New Zealand; correspondence as Commander-in-Chief Central Force, Home Defence, 1914-1915; papers as General Officer Commanding Mediterranean Expeditionary Force on Gallipoli, 1915, including correspondence with FM Horatio Herbert Kitchener, 1st Earl Kitchener of Khartoum and Broome, and the War Office, Rt Hon Winston Leonard Spencer Churchill MP, Lt Gen Sir John Grenfell Maxwell and Lt Gen Sir William Riddell Birdwood; papers relating to Ellis Ashmead Bartlett and Keith Arthur Murdoch, war correspondents on Gallipoli; papers relating to operations at Suvla Bay and Sari Bair, Aug-Sep 1915, and to the efficiency of commanding officers; papers relating to Hamilton's despatches from Gallipoli, and to recommendations for decorations; official despatches, 1914-1919; force orders, intelligence bulletins and other papers of General Headquarters, Mediterranean Expeditionary Force; papers relating to Hamilton's Gallipoli diary; maps and official photographs of the Gallipoli Campaign; depositions of witnesses given to the Dardanelles Commission, with related correspondence, 1916-1919; correspondence with the War Office, 1917-1938; correspondence as Colonel of the Gordon Highlanders, 1912-1949; correspondence relating to ex-servicemen, the British Legion, and to war memorials, 1916-1949; correspondence and papers as Lord Rector of Edinburgh University, 1932-1936; correspondence with major military, political and literary acquaintances, including Rt Hon Winston Leonard Spencer Churchill MP, Rt Hon Richard Burdon Haldane, 1st Viscount Haldane of Cloan, Capt Sir Basil Henry Liddell Hart, John Masefield, FM Sir William Robert Robertson, and senior officers associated with the Gallipoli Campaign, 1916-1949; correspondence relating to the Anglo-German Association and to Anglo-German relations, 1928-1947; correspondence with members of the public and relatives, 1908-1948; business and financial correspondence, 1913-1947; correspondence relating to Hamilton's estate and his literary executors, 1948-1969; papers relating to Hamilton's publications, 1872-1948; speeches, articles and letters to the press, 1918-1947; scrapbooks and press cuttings, 1883-1971; photographs, 1855-1947; publications and other printed material, 1814-1966; diaries, correspondence and publications of Hamilton's wife, Jean Miller Hamilton, Lady Hamilton, 1869-1940; correspondence of Eleanor Charlotte Sellar, 1896-1934, including correspondence with Hamilton, FM Sir George Stuart White and FM Sir Neville Bowles Chamberlain.

Diaries, 1901-1968; papers and photograph albums relating to the Boer War and photography in military reconnaissance, including an unpublished manuscript, 1897-1902, service in Northern Nigeria on the Anglo-French Boundary Commission, 1902-1904, West Africa, 1903, West Indies, 1902 and Ordnance Survey of Scotland, 1904-1909; papers relating to the introduction and use of chemical warfare during World War One, 1914-1918, and on the North West Frontier, India, 1919-1920 andphotographs taken on the Western Front, 1914-1915 and 1919; articles written as Director of Irish Propaganda during the Anglo-Irish War, 1921; papers concerning appointments as Colonel Commandant and Representative Colonel Commandant, 1937-1944; papers concerning writing and publication of 'Gas!' The story of the Special Brigade (Blackwoods, 1934) and Commonsense and ARP (C Arthur Pearson, 1939) and draft chapters and photographs concerning the unpublished manuscript 'Adventures of an Engineer Subaltern' dealing with military career, 1897-1903; personal correspondence and papers relating to memorial service, 1900-1981; glass and film negatives covering career, 1897-1920.

Papers relating to early career, including material on early aviation, 1911-1913, and texts of lectures given at the RAF Staff College, Andover, 1922-1926. Material relating to post as Air Officer Commanding, British Forces in Iraq, 1928-1935, including correspondence, memoranda and telegrams relating to operations in Iraq and Kuwait, 1928-1930, and negotiations for the Anglo-Iraq Treaty, 1930; news cuttings and notes relating to political and military affairs in Iraq, and the situation of the Assyrians and Kurds, 1930-1935. Papers created as Air Officer Commanding in Chief, Air Defence of Great Britain, 1933-1935, mainly relating to a Royal Review of the RAF at Mildenhall, Suffolk, and Duxford, Cambridgeshire. Papers relating to post as Air Officer Commanding in Chief, Middle East, notably memoranda, cypher signals, letters and notes, 1931-1936, relating to RAF operations, mainly planning and preparation for the possibility of war between the League of Nations and Italy following the Italian invasion and annexation of Abyssinia; correspondence with ACM Sir Edward Leonard Ellington, Chief of Air Staff, 1935-1936; memoranda, telegrams, correspondence and newscuttings on operational matters relating to the Arab Rebellion against the British Mandate in Palestine, 1936; material collated by Brooke-Popham for lectures on the Middle East, 1930, 1936; correspondence, memoranda and minutes relating to the formation and working of an Executive Committee on Assyrian Settlement, 1943-1947. Papers relating to the creation and implementation of the Empire Air Training Scheme in Canada and South Africa, 1939-1945, including personal correspondence with Arthur William Street, Permanent Under-Secretary of State for Air, 1940. Papers relating to post as Commander in Chief, Far East, notably telegrams and memoranda relating to the requirements of the RAF and Army in the Far East, 1940-1949; personal correspondence with Maj Gen Sir Hastings Lionel Ismay, Secretary to the Committee of Imperial Defence, 1940-1941; semi-official correspondence with Street, 1940-1941; material relating to the replacement of Brooke-Popham as Commander in Chief, Far East, Nov 1941; telegrams relating to reconnaissance sightings of Japanese convoys, the decision not to launch Operation MATADOR, the outbreak of war with Japan, and the sinking of RN battleships HMS PRINCE OF WALES and HMS REPULSE, Dec 1941; papers, correspondence and proofs relating to the publication of various despatches and reports concerning operations in Malaya, 1941-1947. Papers created whilst Inspector General of the Air Training Corps, 1942-1947, 1950-1952, mainly comprising inspection reports and material relating to the post-war organisation of the Air Training Corps. Booklets, memoranda, and reports collated by Brooke-Popham relating to RAF training, policy and operations, [1914]-1946. Material relating to research for and writing of articles, lectures and pamphlets, mainly relating to history, aviation or training, 1923-1952. Printed material, 1890-1953, mainly relating to aviation. Maps and photographs, 1917-[1945], including aerial photographs of the Western Front during World War One, 1917-1918.