HMS Nepean was an Admiralty M-class destroyer which served in the Royal Navy during the First World War. The M class was an improvement on those of the preceding L class, capable of higher speed. The second Royal Navy vessel to be named after Sir Evan Nepean, and the first not in Australian service, the destroyer was launched in 1916 and joined the Thirteenth Destroyer Flotilla of the Grand Fleet. In 1917, Nepean formed part of the escort for the light cruisers Dublin and Sydney when they were attacked by the Zeppelin L 43 and the First Battlecruiser Squadron during the Second Battle of Heligoland Bight. Neither led to the warship being involved in any action with the enemy. The destroyer finished the war with the Fourth Destroyer Flotilla. After the Armistice, Nepean was placed in reserve before being sold to be broken up in 1921.

The M class, more properly known as the Admiralty M class, were a class of 85 destroyers built for the Royal Navy of United Kingdom that saw service during World War I. All ships were built to an identical – Admiralty – design, hence the class name. 18 other vessels which were officially included within the 'M' class were built to variant designs by three specialist builders – 10 by Yarrow, 6 by Thornycroft, and 2 by Hawthorn Leslie; these are covered in other articles.