RAFVR was a legal means to assemble a force of men in addition the the strength of the RAF approved by civil government.
Militamen, National Servicemen and volunteers were a means of providing the manpower for the RAFVR.
The Royal Air Force was limited by goverment/treasury to a maximium number of men. Although set in peacetime it was still a limit for wartime and was the mechanism that the force would reduce to peacetime levels on cease of hostility.
Need to go back to The Trenchard Memorandum (White Paper Cmd 467:The Permanent Organisation of the Royal Air Force) and 1919 for the genesis but expansion did not really start until the 1930s.
Although the Royal Air Force of 1918 was cut down to a force about 10% of its wartime strength it was recognised that a reserve of trained men would be required to bridge the gap until any new conscripts enrolled at the start of a conflict reached the frontline units.
The Trenchard Memoradum allowed for a reserve force in addition to the manpower in the the Royal Air Force and this was to be in two parts:
Members of the RAF who, after completing short service commissions, were liable to call back to arms for a specified number of years.
The Auxiliary Air Force (the RAF equivalent to the army TA) who would provide an embodiment of men to backfill regular RAF units.
1922 saw the first comprehensive reserve training scheme created.
With the drawdown of RAF manpower from 1918 the number of RAF short service men in the reserve was limited at 200 pilots and seen as reducing so in 1923 it was decided to expand the reserve to 700 officers and 12,000 men made up of two sections, Reserve of Air Force Officers (RAFO) and airmen of the Royal Air Force Reserve.
Classes A, AA, B, BB, C, D, E and F
This was formailsed in the Auxiliary Air Force and Air Force Reserve Act of 1924 and resulted in the creation of Auxiliary and Special Reserve squadrons in 1925.
Under the Reseve act the Auxiliary squadrons were evisaged as acting as a standalone entity taking care of all flying and trade training by use of internal resources. They were also limited to Home use and entry terms prevented airmen being posted to Field force.
Special Reserve squadrons were a cadre unit to be filled at time of mobilisation.
With the expansion of the RAF during the 1930s the supply of pilots into the RAFO dried up as they were retained within the RAF and the Auxiliary Air Force could not expand to provide more trained pilots due to their internal limitations on training.
In Feb 1936 a proposal was made to create a new citizen air force acting as a real second line airforce behind the regular units. This was to be the RAFVR based in town centres and operating from local aerodromes. One of the implications of town base rather than county was that it would appeal to the technical youth of the industrial centres rather than the country gentry that gravitated to the Auxiliary Air Force.
Officer and airmen of the new reserve force would be recruited on a common basis as airman pilot or observer and commission would be on the demonstration of leadership qualities.
In August 1936 the new force was approved and given the name RAFVR. By May 1939 25 aerodrome centres had opened.
As a more flexible force, without any constraint on where the entrants could serve the RAFVR was chosen as the force to accept Militiamen, later National Service Men as well as direct volunteer entry.
The constitution of the RAF, even in wartime, would not allow more men to be employed within the force than had been agreed at treasury budget.
To complete the reserve forces picture was the formation of Civil Air Guard in 1938 where a totally civilian force used the resource of civil flying clubs and schools to train civil pilots to intial standard. Grants were available for this purpose.