Received his medical education at Cambridge and St Mary's Hospital where he qualified LSA in 1888. Obtained the Durham MD in 1906.
26 Nov 1890 Acting-Surgeon R. R. Sleman, 20th Middlesex Rifle Volunteers, was appointed Surgeon, ranking as Captain.
1897 Instructor in the Voluntary Ambulance School Instruction. Received the proficiency certificate of the Army Medical Training School, Aldershot, with special mention.
24 June 1899 Commented on the new Manual of the Royal Army Medical Corps.
11 Oct 1899–31 May 1902 Boer War.
1900 Served in the Transvaal in the South African War as surgeon-major (senior medical officer) in the City of London Imperial Volunteers. Was present at the battles of Zand River, Dornkop, Diamond Hill, and Frederickstadt. He received the South African Medal with four clasps, and the Freedom of the City of London was conferred upon him.
1 Dec 1900 Temporary Captain R. R. Sleman, Medical Officer, 20th Middlesex Volunteer Rifle Corps, was absorbed into the establishment of his Corps on the disbandment of the City of London Imperial Volunteers, and was granted honorary rank in the Army.
10 Sept 1901 Surgeon-Captain R. R. Sleman (20th Middlesex Volunteer Rifle Corps), The City of London Imperial Volunteers.
10 Oct 1903 Attended the Volunteer Ambulance School of Instruction at the HQ of the London Rifle Brigade.
5 Nov 1904 Surgeon-Major (Honorary Captain in the Army) R R Sleman 20th Middlesex Rifle Volunteers (Artists) was granted the honorary rank of Surgeon-Lieutenant Colonel.
Aug 1908 The 1st City of London Field Ambulance under Lt Col R R Sleman VD trained at Larkhill Camp, with the 3rd Brigade under Brigadier F I Maxse CB.
2 July 1910 The medical units of the 1st London Division, headed by their band, proceeded by march route to Philip's Farm, Hendon, under the command of the Administrative Medical Officer, Colonel P B Giles, VD, FRCS. The units on parade were the 1st, 2nd, 3rd Field Ambulances, 1st and 2nd General Hospitals, and the Sanitary Company. The corps returned to London on July 3rd, by march route, under the command of Lt Col R R Sleman.
9 Aug 1913 Attended the 15 days Divisional annual training of the field units of the Royal Army Medical Corps, First London Division (TF), on Salisbury Plain, under the direction of Colonel J. Harper MD, Assistant Director of Medical Services. Three Field Ambulances attended. Lt Col R R Sleman VD MD commanded the First Field Ambulance, Lt Col W. Salisbury Sharp MD FRCSI the Second Field Ambulance, and Lt Col J R Whait MD, the Third Field Ambulance.
5 Mar 1912 In March 1912, the 1st London (City of London) Field Ambulance had an establishment of ten officers and 259 men, but its actual strength was 10 officers and 173 men.
28 July 1914 Start of the Great War.
4 Aug 1914 Britain declares war on Germany.
Assistant Director of Medical Services 58th Division British Expeditionary Force.
5 Aug 1914 1st London Field Ambulance RAMC (T) mobilised and marched to Whitmore Common Worplesdon, Guildford on 25 August. It left the Common for London on 1 September and embarked for Malta on 4 September.
Malta 13 Sept 1914 Arrived in Malta in command of 1st London Field Ambulance RAMC (T). On 3 September Regular RAMC officers were withdrawn from Malta and replaced by four Territorial Force RAMC officers, and 193 other ranks of the 1st London (City of London) Field Ambulance (TF).
14 Sept 1914 DDMS Colonel Michael William Russell L/RAMC returned to England, and the duties of Deputy Director of Medical Services Malta were carried out by Lt Col R. R. Sleman RAMC (TF). Lt Col C. C. Cumming RAMC acted as Deputy Assistant Director of Medical Services.
16 Sept 1914 Appointed Senior Medical Officer (SMO) Malta Command.
13 Nov 1914 Inspected the Prisoner of War Camp at St Clement's Parade Ground, Verdala Barracks.
16 Nov 1914 Was promoted Colonel (Local Rank) AMS while serving at Malta (London Gazette 3 Nov 1914).
8–17 Dec 1914 In-patient at Cottonera Hospital with Influenza.
11 Mar 1915 The Governor Field Marshal Lord Methuen applied to the War Office for a years' extension of Col Sleman's command in Malta as DDMS from 1 April.
Malta Jan–July 1915 ADMS Malta command until July 1915, when the expansion of the hospital base required the presence of a more senior officer. Consequently, Surgeon-General Hayward Reader Whitehead arrived from England and took over the duties of Director of Medical Services Malta. In April 1916, Surgeon-General Whitehead moved on to Salonica, and was succeeded by Surgeon-General Michael Thomas Yarr, who held the appointment till the end of the war.
The base hospitals for the Dardanelles were located at Mudros on the Island of Lemnos, Alexandria, and Malta. The Joint Committee of the British Red Cross and the Order of St John, in addition to its work on the peninsula and at Lemnos, provided comforts of various kinds for the hospitals in Malta and also to hospital ships. Among other such enterprises, it set up a plant for making soda water for one of the hospitals at Malta.
May 1916 Relinquished his temporary commission on vacating his appointment as Assistant Director of Medical Services.
1917–1919 He was an Officer of the Order of St John of Jerusalem, and had been awarded the Volunteer and Territorial Decorations, the Order of the White Eagle of Serbia (1917), and the Order of the League of Mercy in 1919. Dr Sleman was a vice-president of the League of the Order of Mercy and an inspector of hospitals for that League.