Rear Admiral John Saumarez Dumaresq, CB, CVO (/dʊˈmɛrɪk/ duu-MERR-ik;[1] 26 October 1873 – 22 July 1922) was an officer in the Royal Navy.

He served during the First World War but is most remembered as an inventor, for development of the device named after him, the Dumaresq, which helped users calculate the rate at which the range to an enemy ship was changing over time.

Dumaresq attempted to trap the Zeppelin by ordering the accompanying ships to disperse, leaving the Zeppelin attempting to bomb his ship and coming closer, and then ordering them back forming a ring surrounding the enemy.

Dumaresq became convinced of the need for aircraft to operate from ships and a platform to his design was installed on Sydney in October 1917 for the purpose of launching an aeroplane.

During an engagement with enemy destroyers at Heligoland Bight on 1 June 1918, the aircraft was used in action to drive off two attacking German aeroplanes, shooting down one.