There is a new book out there by Sonke Neitzel, Geoffrey Brooks who worked as translator and Ian Kershaw who wrote the Introduction, called “Tapping Hitler’s Generals.”
Apparently the British Intelligence Service has collected dialogues from Hitler’s Generals by placing bugging devices in their cells at Trent Park. From 1942 to 1945, the Generals speak of military defeats, doubts about Hitler’s competency as Commander-in-chief, the failed assassination attempt of Hitler in 1944, and much, much more.
I recommend this book to those researching the German military during World War II.