A little more information to add to Timberman's:
Henlow was known as the Home Aircraft Depot until August 1935 when it became an airframe riggers' school. No.1 Wing trained machine tool operators and Fitter 1; No.2 and No.3 Wings trained flight riggers and flight mechanics. By 1936 it was known as the RAF School of Aeronautical Engineering and included an MT Training Section and a Pilotless Aircraft Section. By February 1939, much of the training had moved to St.Athan and No.2 Mobilisation Pool was formed at Henlow, and No.13 MU had also been formed.
The Armamanet & Gunnery School at Eastchurch moved away in September 1939. It had been there since April 1922 and its role as far as airmen were concerned, was to enable them to become armourers and to enable them to qualify for the Air Gunner's badge.
I hope this helps.
Cliff