Allied escorts vessels regularly put into the British naval base in Gibraltar which is actually connected to Spain. The fascist government of Spain, under murderous Dictator Francisco Franco, maintained theoretical neutrality in WW II but German agents in Spain openly took thousands of photographs of Allied escorts ships in the harbor at Gibraltar. In spite of having all of this photographic evidence, the Germans never figured out what the complex HF/DF aerials were.
Charles McCain is a Washington DC based freelance journalist and novelist. He is the author of "An Honorable German," a World War Two naval epic. You can read more of his work on his website: http://charlesmccain.com/ View all posts by Charles McCain