The Thornycroft M or Mastiff class were a class of six British destroyers completed for the Royal Navy during 1914–16 for World War I service. They were quite different from the Admiralty-designed ships of the Admiralty M-class destroyer, although based on a basic sketch layout provided by the British Admiralty from which J I Thornycroft developed their own design. Like the 'standard' Admiralty M class they had three funnels, but the centre funnel was thicker in the Thornycroft ships. The midships 4 in gun was shipped between the second and third funnels. Patriot was fitted to carry a kite balloon.

Ships

Two ships were ordered (contracted) on 1 February 1913, two more on 26 February 1915 and the last two on 15 May 1915. Note Thornycroft also built six other M-class destroyers for the Royal Navy – Michael, Milbrook, Minion and Munster, all ordered on 20 September 1914, and Nepean and Nereus, both ordered on 20 November 1914; however these were to the Admiralty 'M' design and are included with the article on that large group of destroyers.

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