Royal Navy radio direction finding began well before 1939

When did Royal Navy ships begin receiving radio direction-finding equipment?

Basic direction finding appeared before the First World War, while the forms familiar from anti-submarine warfare became increasingly widespread in the 1930s.

Early radio direction finding predated the anti-U-boat sets familiar from the Second World War. British ships carried the equipment before and during the First World War, and Town-class cruisers used it to hunt German forces. Newer variants spread through the fleet during the 1930s. German habits of transmitting at maximum power and sending lengthy reports made those signals particularly easy to exploit.