1st Anti-Aircraft Group (1 AA Group) was a formation created by the British Army's Anti-Aircraft Command in 1942 to control anti-aircraft (AA) units defending London against Luftwaffe attacks during World War II. It continued this role into the Cold War until disbandment in 1955.

World War II 1 AA Group was formed on 1 October 1942 when Lieutenant-General Sir Frederick 'Tim' Pile, Commander-in-Chief of Anti-Aircraft Command (AA Command), scrapped its previous conventional structure of Corps and Divisions. Each of the new AA Groups was commanded by a major-general and controlled a number of AA Brigades and support units. The new group boundaries were aligned with the Fighter Groups of the Royal Air Force (RAF).Routledge, pp. 400–1; Map 36.Pile.Farndale, Annex J, 'Some Prominent Gunners of World WarII'.Pile at Generals of WWII. (It was jokingly observed that a reorganisation that eliminated eight general officers was the best contribution to the war effort at the time!)

1 AA Group's area of responsibility covered the London Inner Artillery Zone (IAZ) formerly controlled by 1 AA Division, and later included the 'Thames North' and 'Thames South' defences either side of the Thames Estuary from the former 6 AA Division. This tightly defined area was almost surrounded by 2 AA Group covering South East England, and together the two groups mirrored No. 11 Group RAF.Frederick, p. 1047.

The first General Officer Commanding (GOC) of 1 AA Group was Maj-Gen Erroll Tremlett, who had previously commanded 10 AA Division. A former first-class cricketer, Tremlett had distinguished himself earlier in the war when he commanded 54th (Argyll and Sutherland Highlanders) Light Anti-Aircraft Regiment, Royal Artillery defending the mole during the Dunkirk evacuation.Farndale, p. 64.London Gazette 20 December 1940.Tremlett at Generals of WWII.

Order of Battle 1943–44 When they were first established there was much interchange of the units allocated to 1 and 2 AA Groups, but from early 1943 1 AA Group had the following order of battle (temporary attachments omitted):Order of Battle of Non-Field Force Units in the United Kingdom, Part 27: AA Command, 1 October 1942, with amendments, The National Archives (TNA), Kew, file WO 212/82.Order of Battle of Non-Field Force Units in the United Kingdom, Part 27: AA Command, 13 March 1943, with amendments, TNA file WO 212/83.Order of Battle of AA Command, 1 August 1943, with amendments, TNA file WO 212/84.Order of Battle of AA Command, 27 April 1944, with amendments, TNA file WO 212/85. 26 (London) AA Brigade 111 Heavy AA (HAA) Regiment, Royal Artillery (RA) – to 21st Army Group by August 1943Joslen, p. 463. 132 (Mixed) HAA Regiment, RA – to 2 AA Gp July 1944 137 (Mixed) HAA Regiment, RA 156 (Mixed) HAA Regiment, RA 48 AA Brigade 117 HAA Regiment, RA – from Orkney and Shetland Defences (OSDEF) October 1943; to 2 AA Gp May 1944 141 (Mixed) HAA Regiment, RA – to 7 AA Gp December 1943 155 (Mixed) HAA Regiment, RA 160 (Mixed) HAA Regiment, RA – from 2 AA Gp by March 1944 163 (Mixed) HAA Regiment, RA 164 (Mixed) HAA Regiment, RA – left October 1943

49 AA Brigade 141 Light AA (LAA) Regiment, RA – to Gibraltar August 1943Joslen, p. 553. 26 (London Electrical Engineers) (Mixed) Searchlight (S/L) Regiment, RA 80 S/L Regiment, RA – from 4 AA Gp by April 1944 1 (Mixed) AA 'Z' Regiment, RA 6 AA 'Z' Regiment, RA – to 37 AA Bde August 1943 14 AA 'Z' Regiment, RA – to 4 AA Gp April 1943 19 (Mixed) AA 'Z' Regiment, RA 301 Gun Operations Room (GOR), Stanmore 601 GOR, Brompton Road 1 AA Group School, Chelmsford 1 AA Group (Mixed) Practice Camp 1 AA Group Mixed Signal Unit, Royal Corps of Signals (RCS), UxbridgeNalder, pp. 618–9.Lord & Watson, pp. 167, 251. 1 Mixed Signal Company 1 AA Command Mixed Signal Office Section (under AA Command) 1 AA Group Mixed Signal Office Section 26 AA Bde Mixed Signal Office Section 48 AA Bde Mixed Signal Office Section 49 AA Bde Mixed Signal Office Section 4 AA Line Maintenance Section 2 Mixed Signal Company 301 GOR Mixed Signal Section 601 GOR Mixed Signal Section 5 AA Line Maintenance Section HQ 1 AA Group Royal Army Service Corps (RASC) 900, 902, 907 AA (M) Transport Companies 919, 921 AA (M) Transport Companies – joined November 1943 1 AA Group Royal Army Medical Corps (RAMC) Company 1 AA Group Royal Army Ordnance Corps (RAOC) 10 AA Workshop Battalion, Royal Electrical and Mechanical Engineers (REME) 1, 6 AA Workshop Companies 1 AA Group Radio Maintenance Company – later divided into 101 and 102 Radio Maintenance Detachments; joined by 105 Detachment June 1944

'Mixed' indicates that women of the Auxiliary Territorial Service (ATS) were integrated into the unit. HAA regiments were equipped with 3.7-inch guns, LAA regiments with Bofors 40 mm guns, 'Z' Regiments with Z Battery rocket projectors, and S/L regiments with a variety of searchlights and Light machine guns.

By August 1943 the Group had taken over control of two further AA brigades, with the associated signal units:

28 (Thames & Medway) AA Bde – 'Thames South' 148 (M) HAA Regiment 159 (M) HAA Regiment – to 4 AA Gp October 1943 169 (M) HAA Regiment – from 4 AA Gp October 1943 132 LAA Regiment 12 (M) AA 'Z' Regiment – disbanded November 1943Farndale, Annex M. 328 GOR, Fort Luton 37 AA Bde – 'Thames North' 121 HAA Regiment – to 21st Army Group by September 1943 136 HAA Regiment – to 2 AA Gp August 1943 167 (M) HAA Regiment – to 4 AA Gp by September 1943; returned May 1944 184 (M) HAA Regiment – new unit joined by September 1943 137 LAA Regiment – from 3 AA Gp December 1943 6 AA 'Z' Regiment – from 49 AA Bde August 1943; to 26 AA Bde August 1944 329 GOR, Vange 3 Mixed Signal Co 28 AA Bde Mixed Signal Office Section 328 GOR Mixed Signal Section 37 AA Bde Mixed Signal Office Section 329 GOR Mixed Signal Section 15 AA Line Maintenance Section

Z Regiments were termed 'AA Area Mixed Regiments' from April 1944, by which time they were largely operated by ATS and Home Guard personnel.

Baby Blitz The Luftwaffe carried out few bombing raids on London during 1943, preferring to concentrate on 'hit and run' attacks by Fighter-bombers against coastal targets.Collier, Appendix XXXVIII.Routledge, pp. 401–4; Table LXVIII, p. 405. However, in January 1944 it resumed night raids on London, which became known as the 'Baby Blitz'. These raids employed new faster bombers with sophisticated 'pathfinder' techniques and radar jamming. For example, on the night of 21 January 200 hostile aircraft were plotted approaching the South Coast in two waves, which intermingled with returning aircraft of RAF Bomber Command. This caused problems of identification and restrictions on fire, but the guns of 2 AA Group and then 1 AA Group engaged as the raiders approached London. Only one-fifth of the raiders reached the city, the remainder turning away to bomb open country. AA guns brought down eight aircraft and RAF Night fighters with S/L assistance also had successes. At the end of January London Docks received a 130-strong raid dropping flares and incendiaries as they had in the London Blitz of 1940–41: about one-third reached their target and five were shot down. February began with a 75-strong raid, of which only 12 reached the IAZ and four were shot down. On 13 February only six out of 115 bombers reached London. The climax came with five raids in the week 18–25 February varying from 100 to 140 in strength. These met intense AA fire from the Thames Estuary onwards and fewer than half made it to central London: the AA score was 13 shot down while the night fighters and S/Ls added 15, with another shared. Facing these casualty rates, the Luftwaffe switched to targets away from London until 24 March, when a 100-strong raid on London lost four aircraft, and finally on 18 April a raid of 125 aircraft lost 14 shot down and only 30 reached the IAZ. Although much damage was caused in London, the rising efficiency of the HAA guns and radar made the enemy's losses unsustainable.Collier, Chapter XXI.Collier, Table XLII.Routledge, pp. 409–10.

By February 1944, 1 AA Gp was responsible for the AA Operations Room at Brompton Road and the following GORs: 301 Stanmore 320 Hastings 329 Vange 330 Chelmsford together with a number of ordnance depots and miscellaneous establishments, including the AA Command Staff Duties School, Research Workshops and Camouflage Experimental Section, and 37 Radio Installation Detachment. In May 1944 the group was joined by 99 Group, Pioneer Corps, with 801, 809, 814, 817, 818, 841 and 844 semi-mobile smoke companies (in August 801 and 841 Companies were replaced by 4 Company, Non-Combatant Corps).

Operation Diver

AA Command had been steadily losing men and units to the build-up of 21st Army Group for the planned Allied invasion of Europe (Operation Overlord). In April 1944, while the Baby Blitz was still under way, it was ordered to deploy much of its strength to defend the Overlord concentration areas and embarkation ports. In addition, it was preparing for the anticipated arrival of V-1 flying bombs, codenamed 'Divers'. In the event, the first of these did not arrive over England until a week after the D Day landings had begun, and AA units were able to redeploy from their Overlord sites to begin Operation Diver. However, early results of AA fire by 1 and 2 AA Groups against the small, fast, low-flying missiles were disappointing. Even shooting down those that reached the IAZ caused significant damage, so a ban was imposed on fire in this area.Routledge, pp. 408–12.

At the end of June Pile ordered a change in AA Command's tactics: instead of deploying mobile 3.7-inch guns in the Diver Belt, the most up-to-date power-controlled static guns, radars and predictors would be used, which involved a massive redeployment of guns uprooted from all over Britain and emplaced on temporary 'Pile Platforms'. The task was made bigger by the decision to move the Diver Belts to the coast itself, giving the guns a free fire zone out to sea. On 16 July 1 AA Group was ordered to form a 'Diver Box' of gun defences across the Thames Estuary, forward of a line from Chelmsford in Essex to Chatham, Kent. The removal of so many guns, and the silencing of those remaining in the IAZ, led Londoners to believe that the city was being defended by the RAF alone.Routledge, pp. 412–16.

As 21st Army Group began to overrun the V-1 launching sites in Northern France, the Luftwaffe turned to launching the missiles from aircraft over the North Sea, and 1 AA Group's Diver Box was heavily engaged. It was equipped with 136 Mark IIC 3.7-inch guns with No 10 Predictors and SCR-584 radar (some manned by three US Army AA Artillery battalions), 210 Bofors guns, and two Z Batteries of mobile nine-rocket launchers manned by a converted S/L regiment. The HAA guns began using the proximity VT fuze with great success. A number of the guns were mounted on the Maunsell Forts in the Thames Estuary. In addition there were 400 20mm guns provided by the RAF Regiment and the Royal Navy. To control these guns the Box was divided into four sectors under 37, 49, 56 and 68 AA Brigades.Routledge, pp. 413–15.