They had a lot of opsec problems. There's a great story about how using "cool" codenames instead of random ones bit them in the ass.
It's nearly impossible for a bomber to navigate long distances in the dark over a blacked-out country, so the Germans came up with a radio navigation system involving beams transmitted from the mainland to intersect over the target, which the British figured out how to jam; the Germans came up with another nav system, and the Brits eventually jammed that one too.
The British knew the Germans would be trying to find yet another way. They'd learned from Enigma decrypts about a new device called Wotan. One researcher looked up the word, learned that it was the name of a one-eyed god, and concluded that the new system would use a single transmitter with a rangefinding transponder aboard the bomber, instead of multiple beams like the previous ones. Starting from there, they had a countermeasure online and ready to go before the Germans even deployed Wotan. When the Nazis realized they'd been outmaneuvered from the start, they gave up on radio-guided bombing completely, at least against Britain.
To be fair, some of the German spies were pretty bad at their jobs. Josef Jakobs stands out as a man who was just not a good spy: https://en.wikipedia.org/wiki/Josef_Jakobs
Dr. R.V. Jones had significant involvement in the War of the Beams, and after the war wrote a book about British Scientific Intelligence efforts during the war.
It's nearly impossible for a bomber to navigate long distances in the dark over a blacked-out country, so the Germans came up with a radio navigation system involving beams transmitted from the mainland to intersect over the target, which the British figured out how to jam; the Germans came up with another nav system, and the Brits eventually jammed that one too.
The British knew the Germans would be trying to find yet another way. They'd learned from Enigma decrypts about a new device called Wotan. One researcher looked up the word, learned that it was the name of a one-eyed god, and concluded that the new system would use a single transmitter with a rangefinding transponder aboard the bomber, instead of multiple beams like the previous ones. Starting from there, they had a countermeasure online and ready to go before the Germans even deployed Wotan. When the Nazis realized they'd been outmaneuvered from the start, they gave up on radio-guided bombing completely, at least against Britain.