HMS Engadine was a seaplane tender which served in the Royal Navy during the First World War. Converted from the cross-Channel packet ship SS Engadine, she was initially fitted with temporary hangars for three seaplanes for aerial reconnaissance and bombing missions in the North Sea. She participated in the Cuxhaven Raid in late 1914 before she began a more thorough conversion in 1915 that increased her capacity to four aircraft. Engadine was transferred to the Battle Cruiser Fleet in late 1915 and participated in the Battle of Jutland in 1916 when one of her aircraft flew the first heavier-than-air reconnaissance mission during a naval battle. She was transferred to the Mediterranean in 1918.

A seaplane tender is a boat or ship that supports the operation of seaplanes. Some of these vessels, known as seaplane carriers, could not only carry seaplanes but also provided all the facilities needed for their operation; these ships are regarded by some as the first aircraft carriers and appeared just before the First World War.