To be clear: All major navies at the start of the war had decent radio direction finding gear, and the doctrine to use it.
We take for granted in the modern world that the use of active sensors is a tool of last resort since they, duh, give your position away completely. It's astounding that submariners that would have NEVER considered banging away with active sonar on patrol, had no problem using the radio, sometimes multiple times per day. Transmissions that could be DFed not just by nearby enemy warships, but by anyone with a shortwave set back on the mainland. Two guys with radios and a protractor, FTW.
Boggles the mind.
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