There was no teleprinter communication between the HQs and the army commanders. At Gamelin’s HQ there was not even a radio. Gamelin’s usual way of communicating with Georges was to go to him by car. Questioned about the lack of radio, Gamelin said it might have revealed the location of his HQ. Questioned about the speed with which he could get orders to the front, Gamelin said that it generally took forty-eight hours.

— Blitzkrieg by Len Deighton (Page 116)