Aircraft spares delivery in WW2
Given the huge number of aircraft types operated and the rates of loss and damage by the the RAF and USAF in the UK in the Second World War, keeping a steady supply of parts must have been a constant headache. Its well known that the Air Transport Auxiliary delivered complete aircraft, but what about smaller spares? Were all deliveries by road and rail or were parts flown to the end users as well?
As most road signs were removed to hinder any possible German invasion, plus we didn't have the motorway network that we do now, not to mention disruption to the rail network from the larger cities being bombed, its hard to see how any part could get from one end of the country quickly.
Are there any good books or websites which describe how it was done?