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, 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-inch (100 mm) gun was shipped between the second and third funnels. Patriot was fitted to carry a kite balloon.