The primary defence of the aerodrome at this time was the responsibility of the Sherwood Foresters Regiment but in late 1940 this was handed over the Royal Air Force Regiment. In tandem with the upgrade of the airfield defences a bunker at nearby RAF Watnall was constructed to house No. 12 Group RAF (Fighter Command) for the command and control of fighters in their sector; they moved into the bunker in late 1940. No. 12 Group had been based at Hucknall along with No. 1 Group RAF (Bomber Command) since 1939. All the constructed defences are extant with the Flight Office and huts missing.