Royal Auxiliary Air Force

The Royal Auxiliary Air Force (RAuxAF), formerly the Auxiliary Air Force (AAF), together with the Air Force Reserve, is a component of His Majesty's Reserve Air Forces (Reserve Forces Act 1996, Part 1, Para 1,(2),(c)). It provides a primary reinforcement capability for the regular service, and consists of paid volunteers who give up some of their weekends, evenings and holidays to train at one of a number of squadrons around the United Kingdom.

Source: Wikipedia — Royal Auxiliary Air Force (CC BY-SA 4.0)