Churchill & The secret service is a better biography than most of the actual biography books. It explains the creation of a modern secret service used to gather intelligence on foreign and local targets including competing political parties.

This played a major role on Churchill's intuition and ascend, and failed miserably when he diverted resources to fight local political parties thus not predicting the start date of two world wars.

After the wars had started, he did divert resources to handle things succesfully.

TLDR: Churchill was his secret services. Succesful when not adapted to his own personal biases

https://www.amazon.com/Churchill-Secret-Service-David-Staffo...

They organized airplane flyovers that "saw" the U-boats. The Germans did not know how many aircrafts were patrolling and whether it was a high or low probability of being spotted.

If the British could not organize a parallel construction they simply let it go. They knew the plan for Crete invasion but they could not create a story on how they learned it so they preferred to lose naval control of the large part of the eastern Mediterranean sea. [0]

[0] https://www.amazon.com/Churchill-Secret-Service-David-Staffo...