After war was declared on 3 September there were numerous adjustments to AA Command's deployment as further units and equipment became available.
During the autumn 79th (HY) AA Rgt handed over most of its responsibilities for airfields, and shifted towards the Gun Defence Area (GDA) round the port of Harwich and adjacent harbours, where Lt-Col Bazley-Green was appointed AA Defence Commander (AADC) with a Gun Operations Room (GOR) at Harwich:
RHQ at Stansted Mountfitchet, later Felixstowe
246 Bty:
4 x 3-inch at site H1 (Landguard Common, Felixstowe)
20 x AA LMG at Royal Naval Mining Depot, Wrabness
20 x AA LMG at Murex Works, Rainham
247 Bty:
2 x 3-inch at site A1 (RAF Bentley Priory)
2 x 3-inch at site A2 (RAF Bentley Priory)
2 x 3-inch at site H5 (Beacon Hill Battery, Harwich)
248 Bty:
2 x 3.7-inch at site H2 (Trimley, Felixstowe)
2 x 3.7-inch at site H3 (Dovercourt)
20 x AA LMG at RAF Martlesham Heath
20 x AA LMG at Parkeston Quay, Harwich
(The Royal Navy submarine depot ship HMS Cyclops in Harwich harbour was designated as AA site H4 under the GOR)
On 17 October the regiment fired its first rounds in anger, when sites H2 and H3 engaged an aircraft identified as hostile.
During this period a draft of 100-plus recruits (Militiamen with 3 months' AA training) was received for each battery, and training began for 'Operators, Fire Control' who would man RDF (radar) sets when they arrived.

On 26 December a warning order was received to prepare to move overseas, and the detachments concentrated at Harwich.
The regiment was designated as a base defence AA regiment to man static 3.7-inch guns.
248 Battery was already experienced with the 3.7-inch and only needed to attend short courses by sections on a static gun site at Dartford before mobilising at Blackdown Camp near Aldershot, whereas 246 and 247 Btys went to 208th AA Training Rgt at Yeovil and 209th AA Training Rgt at Blandford respectively, followed by two weeks at No 4 AA Practice Camp at Tŷ Croes on Anglesey and No 1 AA Practice Camp at Aberporth in West Wales respectively.
After war was declared on 3 September there were numerous adjustments to AA Command's deployment as further units and equipment became available. During the autumn 79th (HY) AA Rgt handed over most of its responsibilities for airfields, and shifted towards the Gun Defence Area (GDA) round the port of Harwich and adjacent harbours, where Lt-Col Bazley-Green was appointed AA Defence Commander (AADC) with a Gun Operations Room (GOR) at Harwich:
RHQ at Stansted Mountfitchet, later Felixstowe
246 Bty:
4 x 3-inch at site H1 (Landguard Common, Felixstowe)
20 x AA LMG at Royal Naval Mining Depot, Wrabness
20 x AA LMG at Murex Works, Rainham
247 Bty:
2 x 3-inch at site A1 (RAF Bentley Priory)
2 x 3-inch at site A2 (RAF Bentley Priory)
2 x 3-inch at site H5 (Beacon Hill Battery, Harwich)
248 Bty:
2 x 3.7-inch at site H2 (Trimley, Felixstowe)
2 x 3.7-inch at site H3 (Dovercourt)
20 x AA LMG at RAF Martlesham Heath
20 x AA LMG at Parkeston Quay, Harwich
(The Royal Navy submarine depot ship HMS Cyclops in Harwich harbour was designated as AA site H4 under the GOR)
On 17 October the regiment fired its first rounds in anger, when sites H2 and H3 engaged an aircraft identified as hostile. During this period a draft of 100-plus recruits (Militiamen with 3 months' AA training) was received for each battery, and training began for 'Operators, Fire Control' who would man RDF (radar) sets when they arrived.
On 26 December a warning order was received to prepare to move overseas, and the detachments concentrated at Harwich. The regiment was designated as a base defence AA regiment to man static 3.7-inch guns. 248 Battery was already experienced with the 3.7-inch and only needed to attend short courses by sections on a static gun site at Dartford before mobilising at Blackdown Camp near Aldershot, whereas 246 and 247 Btys went to 208th AA Training Rgt at Yeovil and 209th AA Training Rgt at Blandford respectively, followed by two weeks at No 4 AA Practice Camp at Tŷ Croes on Anglesey and No 1 AA Practice Camp at Aberporth in West Wales respectively.
79th (Hertfordshire Yeomanry) Heavy Anti-Aircraft Regiment, Royal Artillery