Vice-Admiral Henry Boyle Townshend Somerville CMG (7 September 1863 – 24 March 1936) was an Irish naval officer who served in the Royal Navy as a hydrographic surveyor.

He was an author of scholarly works as well as of popular accounts of his surveying activities and the comprehensive Ocean Passages of the World.

[4] As a lieutenant, Somerville worked on the surveys of the Queensland coast and the New Hebrides, now Vanuatu, in the South Pacific, (HMS Dart, 1890–91).

[12] Henry Balfour, curator of the museum, wrote an article in 1905 discussing bird and human designs in the Solomon Islands, making use of material collected by Somerville.

[1] In 1895, working on the survey of Tonga, also on Penguin, Somerville took the opportunity to visit Niuafo'ou, and published an early description of the island.

[13] In 1897, Somerville joined HMS Egeria working mostly in British Columbia, but with some surveying in western South America and the Pacific.

[2] In the summer of 1905, Somerville and HMS Sealark were assigned to the Indian Ocean expedition sponsored by the Percy Sladen Trust, which was led by J. Stanley Gardiner.

[24] Shortly before the First World War, Somerville developed a steam-operated sounding machine for determining ocean depth from a ship that was under way.

He thereafter devoted much of his time to surveying and in some cases excavating, such monuments in Britain, Ireland and elsewhere, and became a recognised expert in the field of archaeoastronomy.

With no safe harbours in these islands the ships were always at sea during the night, taking on coal only during daylight hours, to reduce the risk of submarine attacks.

[32] Somerville was involved in the "diplomacy of force" with the Spanish authorities to prevent violations of neutrality, both regarding use of radio communications and port facilities by the Germans.

In October 1914 this led to the internment in La Palma of the Macedonia, a neutral-flagged vessel believed to be provisioning the German commerce-raider SMS Karlsruhe.

[2] One incident he describes from this period was The Great Search of the ship conveying the German Ambassador Count Bernstorff from the United States back to Germany after diplomatic relations were discontinued.

[35] As part of the late summer 1917 reorganisation of the burgeoning British Secret Intelligence Service, led by Mansfield Smith-Cumming and his de facto deputy, Colonel Freddie Browning, Somerville was appointed as "officer in charge of the Naval Section within the Secret Service Bureau".

During his retirement He continued to work for the Admiralty, in the Hydrographic Department and on the Tidal Committee,[3] and published several books including Ocean Passages for the World in 1923.