However, he was unsuccessful in promoting a single cipher agency to coordinate all operations, as was demanded by OKW/Chi and was still blocked by Joachim von Ribbentrop, Heinrich Himmler and Hermann Göring until autumn 1943.

It was not achieved until General Albert Praun took over the post[1] following Fellgiebel's arrest and execution for his role in the 20 July attempted coup.

As head of Hitler's signal services, Fellgiebel knew every military secret, including Wernher von Braun's rocketry work at the Peenemünde Army Research Center.

In the 1938 September Conspiracy to topple Hitler and the Nazi party on the eve of the Munich Agreement, he was supposed to cut communications throughout Germany while Field Marshal Erwin von Witzleben would occupy Berlin.

[4] Fellgiebel was involved in the preparations for Operation Valkyrie and during the attempt on the Führer's life on 20 July 1944[5] tried to cut Hitler's headquarters at the Wolf's Lair in East Prussia off from all telecommunication connections.

Fellgiebel's most famous act that day was his telephone report to his co-conspirator General Fritz Thiele at the Bendlerblock, after he was informed that Hitler was still alive: "Etwas Furchtbares ist passiert!