The Royal Navy entered the war with an established support fleet. In the mid-1930s the RFA operated about forty-one tankers, fifteen harbour tankers, and three aviation-fuel carriers, with Dale-class ships expanding the force. Many vessels were older, but they remained serviceable and several 16-knot Leaf-class oilers lasted through the war. The approximate 1939 total excludes chartered, captured, and merchant vessels, so it describes a core purpose-built force rather than every tanker available.
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Interwar RFA tanker strength
By 1939 the RFA had roughly forty-nine purpose-built oilers, supplemented by harbour tankers and aviation-fuel ships.