Sir Eustace Henry William Tennyson d'Eyncourt, 1st Baronet, KCB, FRS (1 April 1868 – 1 February 1951) was a British naval architect and engineer. As Director of Naval Construction for the Royal Navy, 1912–1924, he was responsible for the design and construction of some of the most famous British warships. On 20 February 1915 Winston Churchill appointed him Chairman of the Landships Committee at the Admiralty, which was responsible for the design and production of the first military tanks to be used in warfare. D'Eyncourt was related to the politician Charles Tennyson d'Eyncourt (d. 1861), uncle of the poet Alfred Lord Tennyson. He was also related to Admiral Edwin Tennyson d’Eyncourt.