High Quality Content by WIKIPEDIA articles! The Gloster Gamecock was a biplane fighter of the Royal Air Force, a development of the Mk III Grebe, that first flew in February 1925. It differed from the Grebe primarily by way of its Bristol Jupiter engine, which replaced the unreliable Armstrong Siddeley Jaguar. Other changes included improved ailerons, refined fuselage contours, and internally mounted machine guns.