Although it is as yet unclear how long McMahon may have remained in the United States after being discharged from the 7th Cavalry by 1896 he had arrived in South Africa and enlisted as a trooper in the Matabeleland Mounted Police. He served as a Lance Corporal in "B" Troop of the British South Africa Company Police and took part in the infamous 1895-6 raid into the Transvaal led by Dr Leander Starr Jameson. McMahon was captured by the Boers when the expedition was forced to surrender at Doornkop on 1 January 1896. Released by the Boers, he was allowed to return to the Cape.

Joining the Matabeleland Relief Force as a trooper he served during the Matabele Rebellion of 1896 and then with the Fort Tuli Detachment of the British South Africa Police by which time he had been promoted to the rank of Sergeant. Although he is listed as a member of the Matabeleland Relief Force I have not been able to find him listed on the medal rolls for the British South Africa Company's Medal. If McMahon did have an entitlement for this medal it would in all likelihood be for the "Rhodesia 1896" medal without a clasp.

He spent about a year attached to the Cape Police Criminal Investigation Department before joining the Rhodesia Regiment as a sergeant in "B" Troop at the outbreak of the Anglo-Boer War. He took part in the Relief of Mafeking and single-handedly captured the flag of the Rustenburg Commando. He saw action at Johannesburg and Diamond Hill. With his term in the Rhodesia Regiment expired McMahon enlisted in the South African Constabulary as a Sergeant Major in "C" Division.

He saw more action in the Orange Free State before being finally discharged in June 1902. The above photograph was taken around this time. He probably wears the ribbons for the Queen's South Africa Medal and the King's South Africa Medal. He was entitled to the following clasps for the Queen's South Africa Medal: "Johannesberg", "Diamond Hill", "Relief of Mafeking", "Orange Free State", "Transvaal" and "Rhodesia".

 
After the war, he apparently worked as a prosecutor with the Transvaal Civil Service although I have found no evidence that he had any formal education in law.

Sometime around 1905 McMahon emigrated to Vancouver, British Columbia and married Miss Marie Morrow and spent the years leading up to World War One working for the Canadian Civil Service

With the outbreak of World War One McMahon would return to England with the Canadian Expeditionary Force but quickly transferred into the British Expeditionary Force being posted as a Temporary Lieutenant with the 10th Battalion, The East Lancashire Regiment.  Promoted to Temporary Captain he was appointed Adjutant with the 10th Battalion on 18 December 1914. His World War One Medal Index Card shows McMahon being attached to the 1st battalion of the Royal Dublin Fusiliers and deploying with that battalion to Gallipoli in July 1915. Seriously wounded in December 1915 he was evacuated back to England and upon recovery was attached to a reserve battalion of the Worcestershire Regiment with the proviso that he was medically unfit for active service and would spend the rest of the war in the Southern Command Intelligence Department. For his war services, he was entitled to the 1914-15 Star, the British War Medal and the British Victory Medal.

Returning to Canada after the war he would return to the Civil Service and retired after some thirty years in 1936. As unlikely as it may seem Robert D.E. McMahon returned to Britain during World War II with the Army Officers Emergency Reserve working at the Royal Ordnance Works at Bedfordshire. For his World War Two service, he may have been entitled to the British War Medal 1939-45.

McMahon returned to Vancouver after the war but in 1953 moved to Rhodesia where he remained until his death at Salisbury on 1 January 1961.

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Cabinet Photograph

F.W. Drieselmann - Photographer
Heidelberg, South Africa
24 May 1902