In this episode, I explain how the British Expeditionary Force was divided into Armies and Corps. I show how the number of armies increased, to accommodate the large numbers of divisions moving to France and Flanders. I then look at the different roles of the armies and corps, when they were just holding the line and when they were attacking. Next we see how the different staff officers dealt with the artillery, engineering, communications, supplies, transport, ordnance and casualties. I close with a brief look at the various support services required by the corps.