Colonel Denis Moriarty O'Callaghan was the youngest son of Mr Robert Charles O'Callaghan LLD of The Rectory, Holton, Suffolk and Bridget Moriarty. He was educated at Queen's College, Cork and at the Carmichael School Dublin, where he took the LRCSI in 1884 and the LKQCP in 1885.
He entered the service on 28 July 1886; rose to the rank of Colonel on 1 March 1915, and retired on 11 December 1918. He served with the Ashanti Expedition of 1895–1896 receiving the Star; with the Nile Expedition of 1898 being present at the Battle of Khartoum, was mentioned in dispatches (London Gazette 30 September 1898) and received the Egyptian Medal with Clasp.
The London Gazette of 30 September 1898 contains the despatch of Sir Herbert Kitchener, Sirdar of the Egyptian Army, describing the operations in the Sudan of the troops under his command, culminating in the battle at Omdurman on 2 September. Sir Francis Grenfell, the General Officer in Command of the forces in Egypt, in forwarding the despatch, acknowledges the services among others, of Surgeon General Henry Skey Muir MD Principal Medical Officer in Egypt. Sir Herbert Kitchener, after relating the nature of the service undertaken by the troops, goes on to say:
The medical department was administered with ability and skill by Surgeon General Taylor, Principal Medical Officer, who was well assisted by Colonel McNamara, whilst the medical organisation of the Egyptian Army fully maintained its previous excellent reputation under the direction of Lieutenant Colonel Gallwey and his staff. The general medical arrangements were all that could have been desired, and I believe the minimum of pain and maximum of comfort procurable on active service in this country was attained by the unremitting energy, untiring zeal and devotion to their duty of the entire medical staff.
Major D M O'Callaghan was among the officers of the Royal Army Medical Corps who was specially brought to notice.
In the South African War of 1900–1901 he was present at the operations in Orange River Colony, including the action at Wittebergen, operations in Cape Colony, south of Orange River, receiving the Queen's Medal with three Clasps.
During the war of 1914–1919, he was mentioned in dispatches (London Gazette 1 January 1916, 29 May 1917, 25 May 1918 and 30 December 1918). He was created CMG in 1917 and received the 1914 Star with Clasp, the British War Medal and the Victory Medal.
Service Record — Denis Moriarty O'Callaghan
28 July 1886 Appointed Surgeon on probation.
Sept 1886 Confirmed in rank as Surgeon.
July 1888 Change of Station from Curragh to Cyprus.
1895–1896 Served in the Third Anglo Ashanti War.
July 1896 Posted to Aldershot.
Sept 1896 Change of Station from Aldershot to Portsmouth.
Oct 1896 Surgeon Captain D M O'Callaghan moved from Portsmouth to Portland.
Apr 1897 Change of Station from Portland to Malta.
19 Apr 1897 Arrived at Malta from Portland, England.
6 Apr 1898 Embarked for Egypt.
Served on the Expedition to Khartoum in the Sudan.
28 July 1898 Promoted Major RAMC.
Apr 1899 Change of Station from Crete to Malta.
Apr 1899 Arrived at Malta from Crete.
12 Jan 1900 Left Malta for Aldershot, England.
Mar 1900 Change of Station from Aldershot to South Africa.
July 1901 Returned to England from South Africa.
Mar 1902 Change of Station from South Africa to Lichfield.
Aug 1902 Change of Station from Lichfield to Malta.
12 Aug 1902 Arrived from Lichfield, England.
24 Nov 1903 Left Malta for Colchester.
Feb 1904 Change of Station from Colchester to Bedford.
Apr 1904 Change of Station from Bedford to Colchester.
28 July 1906 Promoted Lieutenant Colonel RAMC.
Oct 1906 Change of Station from Weedon to India.
Jan 1907 Posted to Rawalpindi.
June 1907 Placed in charge of the Station Hospital, Kuldana.
Sept 1907 Change of Station from Rawalpindi to Kuldana.
Feb 1908 Change of Station from Kuldana to Rawalpindi.
June 1909 Change of Station from Rawalpindi to Kuldana.
Feb 1910 Change of Station from Kuldana to Aldershot.
1912 Married Katherine, eldest daughter of Mrs Sayer of Yewtree House Westfield, Sussex.
Mar 1913 Change of Station from Aldershot to Hilsea.
Placed in medical charge of the Military Hospital at Hilsea.
Feb 1914 Change of Station from Hilsea to Dover.
Was placed in medical charge of the Military Hospital at Dover.
1 Apr 1914 Birth of a son, Denis Sayer at Dorset House, Dorset Square S W.
28 July 1914 Start of the Great War.
4 Aug 1914 Britain declares war on Germany.
1 Mar 1915 Promoted Colonel L/RAMC.
30 Nov 1915 Mentioned in Field Marshal Lord French's dispatch of 30 November 1915 for gallant and distinguished service in the field while serving with the General Head Quarters Staff.
May 1917 Appointed a Companion of The Order of St Michael and St George in the King's Birthday Honours list for services rendered in connection with military operations in the field.
7 April 1918 One of the medical officers mentioned by Sir Douglas Haig in his dispatch dated 7 April 1918, for
distinguished and gallant services and devotion to duty between 25 September 1917 and 25 February 1918.
11 Dec 1918 Placed on retired pay.
21 Aug 1919 Birth of a daughter, Madeline O'Callaghan.
6 Nov 1926 Died at Budleigh Salterton, East Devon.