Henry David Laffan, Royal Engineer, was the son of Lieutenant-General Sir Robert M. Laffan. He was educated at Shrewsbury and at the Royal Military Academy at Woolwich and entered the British Army in 1877. In June 1883, then a lieutenant in the Royal Engineers, he arrived at Durban as a member of a survey party that included 14 non-commissioned officers and was led by Captain W. Morris*. Their task was to commence the geodetic survey of the Cape Colony and Natal, organised and supervised by Dr David Gill* of the Royal observatory, Cape of Good Hope. The work started with the measurement of a baseline near Pietermaritzburg in September and October, and by the end of the year a geodetic chain had been reconnoitred between Newcastle in the north and Kokstad in the South. During 1884 beacons were set up southwards to Kokstad, angular measurements taken, the latitude and azimuth of two stations determined, and the longitude of a third established by means of a telegraph connection with the Royal Observatory in Cape Town.
However, the Natal government expressed itself in favour of a quicker, less costly and less accurate survey extending over a larger portion of the colony, to connect its detached cadastral surveys and serve as the basis for maps. Hence Laffan, with four non-commissioned officers, commenced a secondary triangulation in September 1884 to connect the geodetic chain with the transit pier at the Natal observatory in Durban. After completing this task they commenced the survey of a further set of triangles to the east of the geodetic chain. This work was handed over for completion to A. Mair* when Laffan rejoined Captain Morris at Kokstad in September 1885 for the continuation of the geodetic survey into the Cape Colony. After the triangulation of the Transkei Laffan was temporarily relieved of his duties to save costs. In 1888 he was promoted to Captain and transferred from the geodetic survey to the survey of British Bechuanaland (now part of the Northern Cape). During that year he measured a baseline in the valley of the Dry Harts River, along the Kimberley-Vryburg railway line. He determined the latitude, longitude and azimuth with great accuracy at one of the terminal points, the longitude by means of a telegraph connection with the Royal Observatory. The baseline was used that same year as the starting point of J.J. Bosman's* survey to the border between British Bechuanaland and German South West Africa (now Namibia).
Laffan returned to Britain in 1889. He was promoted to Major in 1895 and from 1896 to 1898 served as deputy assistant adjutant-general in the Intelligence Division of the War Office. In the latter year he completed a Handbook of the Swiss Army, which was published by the War Office. That year the governments of Great Britain and Germany decided to undertake a joint survey to accurately establish the border between German South West Africa and the territories British Bechuanaland and Bechuanaland (now Botswana). South of 22 degrees South latitude the border had been defined in 1890 as running along the 20 degrees East meridian, and the aim of the survey was to beacon it from the northern end of Bosman's survey near Rietfontein up to 22 degrees South latitude. Laffan was appointed British commissioner for the survey, while Germany was initially represented by Lieutenant Wettstein. The field work was conducted between January 1899 and October 1903 under very difficult circumstances, owing to the scarcity of water. To avoid the shifting sands of the Kalahari the chain of triangles had to be measured via Gibeon in German South West Africa. The results of the survey were described by Laffan and others in Report on the boundary survey between British Bechuanaland and German S.W. Africa... published in Berlin in 1906.
In 1903 Laffan was promoted to Lieutenant-Colonel, and in 1906 to Brevet Colonel. He married Anna Bennet in 1904. From that year to 1908 he served as commanding Royal Engineer in the Woolwich District. He was honoured as a Companion of the Order of St Michael and St George (CMG) in 1906. His last known address was in Namibia.