The fast-oiler force expanded during the war

How many high-speed fleet oilers did the Royal Navy have at the beginning and end of the war?

About six at the beginning and closer to twenty by the end of the Second World War.

The brief comparison gives a useful measure of wartime adaptation. Six fast oilers were available at the beginning of the conflict. The estimate rises to nearer twenty by the end. The increase helps distinguish limited prewar specialization from the larger support fleet created as operational demand and industrial capacity expanded.