The big air raids in Coventry are believed to be an example for this. The british knew in advance of it, because of Enigma, but did not made special preparation

The big air raids in Coventry are believed to be an example for this. The british knew in advance of it, because of Enigma, but did not made special preparations, to keep the bigger advantage. I learned this as a fact, but upon checking now, it likely has been a rumor/conspiracy. But there surely are other, real examples.