Sir Eustace Henry William Tennyson d'Eyncourt, 1st Baronet KCB FRS[1] (1 April 1868 – 1 February 1951)[2] was a British naval architect and engineer.

As an apprentice at Armstrong, Whitworth & Co., d'Eyncourt worked on the design of warships for the Austrian, Italian, Norwegian, Spanish, Portuguese, and Turkish governments.

On 20 February 1915, First Lord of the Admiralty Winston Churchill asked him to be Chairman of the Landship Committee, a group of Royal Naval Air Service officers and engineers assembled to design a vehicle capable of crossing No Man's Land and suppressing the enemy machine guns that had caused heavy casualties in the first six months of the First World War.

The result was a hull structure of great strength, and the sloping sides increased the possible spread of impact of shells, thus giving greater resistance to penetration.

The aesthetic side of naval architecture has seldom been given much attention, though it is as much of an art as the architecture of buildings; in general appearance (in terms of harmonious proportion as regards length, beam, and freeboard, as well as the size of the superstructure and funnels in relation to the hull), the opinion has been expressed that d'Eyncourt created some of the most elegant and eye-pleasing warships ever designed, the prime example being the battle cruiser HMS Hood.

Monitors, patrol boats, minesweepers, sloops, gunboats for China Station, Merchant ship conversions into seaplane carriers D'Eyncourt was chairman of the Landship Committee, created by Winston Churchill, which oversaw the design and production of Britain's first military tanks during World War 1.