The RAF 4 is a British air-cooled, V12 engine developed for aircraft use during World War I.

Based on the eight–cylinder RAF 1 it was designed by the Royal Aircraft Factory but produced by the two British companies of Daimler and Siddeley-Deasy.

The RAF 5 was a pusher version of the same engine.

The engine was test-flown in a R.E.8, but the turbocharging experiments were abandoned after the turbine failed on 4 May 1918.

[2] A preserved RAF 4a engine is on public display at the Science Museum (London).