The Reid and Sigrist R.S.3 Desford is a British twin-engined, three-seat advanced trainer developed in the Second World War for postwar use. Although the R.S.3 was evaluated as a trainer, the type never entered production and was eventually rebuilt as the R.S.4 Bobsleigh as an experimental aircraft with the pilot in a prone position, seen as advantageous in minimising g-force effects in fighters.

Reid and Sigrist was an English engineering company based at New Malden in Surrey. It later acquired sites at Desford and Braunstone in Leicestershire. Initially it developed and manufactured aircraft instrumentation and pilot selection aids but later diversified into flying training and aircraft design. During World War II the company was part of the Civilian Repair Organisation repairing, rebuilding and converting warplanes at the Desford site. Post-war, it continued to manufacture aviation instruments and guidance systems but also diversified further to produce cameras and optical instruments. In 1954, the company was purchased and taken over by the Decca Record Company.