5 Feb 1881 Surgeon afterwards Surgeon–Captain.
Malta 12 July 1882 Arrived from Gibraltar.
22 July 1882 Embarked for service in Egypt.
1884–1885 Served in the Sudan.
Apr 1889 Took up his appointment as Adjutant to the Training School at Aldershot.1
Malta 10 Mar 1892 Arrived from Aldershot England.
Malta 5 Feb 1893 Promoted Surgeon-Major.
Malta 27 Mar 1893 To England on sick leave.
Malta 22 Sept 1893 Returned to Malta.
Malta 10 July 1894 Placed on sick leave.
Resident on 11 Sept 1894 at 1D Strada Zaccaria Valletta.
18 October 1894 Returned to England.
1899–1902 Served in South Africa.
5 Feb 1901 Promoted Lieutenant Colonel.
Was granted the local rank of Colonel whilst PMO of a General Hospital in South Africa.
8 June 1907 Retired.
3 Feb 1912 At St Mary's Sholing, Lieutenant Colonel George Edward Twiss FRCSI RAMC (retd.) of St John's Sholing, Hants, married Ethel Madeline, elder daughter of the late Arthur John Sprague, of the Chestnuts Kimbolton, Hants.
5 Aug 1914 Re-employed during the Great War.
Commanded Eastleigh Casualty Clearing Station (1915 – 1919) near Southampton.
Eastleigh Casualty Clearing Station opened in April 1915. It was at first established in a school and a small drill hall, but expanded into a larger drill hall, a railway institute and several small Armstrong huts. This increased its capacity from 220 beds in July 1915, to 1,280 beds in March 1917.
This medical unit was initially called a Clearing Hospital. However, in April 1917, its name changed to that of Military Hospital Eastleigh, when it treated minor injuries and bedded down sick soldiers. In January 1918, the designation was again changed to Casualty Clearing Station Eastleigh. It triaged casualties disembarking directly from hospital ships. The walking casualties were transferred to other hospitals by ordinary passenger trains or discharged as fit for duty after two or three weeks stay in a unit. Those patients still unfit after 14 days were admitted to a military hospital.
Lt Col George Edward Twiss was the author of a Manual for St John Voluntary Aid Detachments (1 January 1916), and a Manual for St John Ambulance Companies (1 January 1911).