A2-31 SE5A biplane illustration by Jamie and Leanne Tufrey - Bunbury, Australia

The Royal Aircraft Factory S.E.5 is a British biplane fighter aircraft of the First World War. It was developed at the Royal Aircraft Factory by a team consisting of Henry Folland, John Kenworthy and Major Frank Goodden. It was one of the fastest aircraft of the war, while being both stable and relatively manoeuvrable. According to aviation author Robert Jackson, the S.E.5 was: "the nimble fighter that has since been described as the 'Spitfire of World War One'".

The initial models of the S.E.5a differed from late production examples of the S.E.5 only in the type of engine installed – a geared 200 hp Hispano-Suiza 8b, often turning a large clockwise-rotation four-bladed propeller, replacing the 150 hp H.S. 8A model.