|Country United Kingdom|
Type Anti-Aircraft Division
|Branch Territorial Army|
Role Air Defence
|Active 15 December 1935 – 30 September 1942|
Part of London District (1935–39) Anti-Aircraft Command (1939–40) 1 AA Corps (1940–42)
The 1st Anti-Aircraft Division (1 AA Division) was an Air Defence formation of the British Army before and during the early years of World War II. It defended London during the Battle of Britain and The Blitz.
1st AA Division was organised on 15 December 1935 at Hillingdon House, RAF Uxbridge (at that time the headquarters of the Royal Observer Corps).
Responsible to London District but under the operational control of RAF Fighter Command, the Division's role was to command the growing number of Territorial Army (TA) anti-aircraft gun and searchlight units around London (2 AA Division was in formed in 1936 to cover the rest of the country). The headquarters of the division was formed by converting 47th (2nd London) Infantry Division, whose General Officer Commanding, Major-General R.H.D. Thomson, continued as GOC of the new formation. Thomson had been Commander TA Air Defence Brigades and Inspector of Regular AA Units, and thus already responsible for the four brigades or 'groups' that comprised the division. He also chaired the War Office committee on expansion and mobilisation of TA AA units, which sat from 1935 to 1937. Tompson was followed in 1937 by Maj-Gen Sir Frederick Pile, who was promoted in 1939 to command the whole of Anti-Aircraft Command.
Order of Battle 1935
1 AA Division was initially composed of the following formations and units:
(In 1938 the Royal Artillery replaced the unit designation 'Brigade' by 'Regiment', which allowed the AA Groups to take the more usual formation title of Brigades.)
The AA Divisions were unlike field formations: they were established to organise training and later exercise operational command in the static conditions of home defence, but relied entirely on the Home Forces commands for logistic support, supplies, and heavy repairs.
The TA's AA units were mobilised on 23 September 1938 during the Munich Crisis. The staff of 1st AA Division now had to implement the Tompson Committee's plan. The call-out of key parties by telephone and telegram went well, and they assembled at their drill halls within a few hours. Because the units possessed only a small scale of transport, elaborate plans had been made to requisition civilian vehicles, ranging from heavy lorries to buses and private cars. Equipment was drawn from mobilisation stores, and the detachments ferried out to their war stations. Despite some failures and problems, the emergency positions covering London were manned and most of the equipment was in place within 24 hours. The emergency mobilisation lasted nearly three weeks before the TA units were released on 14 October. The experience brought about improvements in equipment scales, and a rapid expansion of AA defences brought many new AA gun and searchlight units into existence, some by conversion of TA infantry battalions.
The existing divisions and brigades were expanded, and the whole AA defence of the United Kingdom was taken over by Anti-Aircraft Command on 1 April 1939. A new 6th AA Division was formed by duplicating 1st AA Division's HQ at Uxbridge. 6th AA Division took over responsibility for defending the Thames Estuary and the adjacent areas of Essex and North Kent, allowing 1st AA Division to concentrate on the defence of London. 27th, 28th and 29th AA Brigades were transferred to the new formation.
The deterioration in international relations during 1939 led to a partial mobilisation in June, and a proportion of TA AA units manned their war stations under a rotation system known as 'Couverture'. Full mobilisation of AA Command came in August 1939, ahead of the declaration of war on 3 September 1939.
Order of Battle 1939
When the UK declared war on 3 September 1939, 1 AA Division had the following composition:
GOC: Major-General F.L.M. Crossman, DSO, MC
HQ: Hillingdon House, RAF Uxbridge
In August 1940 the RE 'Anti-Aircraft' (searchlight) battalions became regiments of the RA. Royal Artillery AA units were now designated Heavy Anti-Aircraft (HAA), Light Anti-Aircraft (LAA), or Searchlight (S/L) regiments and batteries.
1st AA Division had established a control centre at a disused Underground station at Brompton Road. The tunnels, subways and lift-shafts were adapted to provide bomb-proof accommodation for a Central Operation Room reporting direct to HQ No. 11 Group RAF at Uxbridge, and four Gun Operations Rooms (GORs) subdividing the London Inner Artillery Zone (IAZ). An elaborate network of dedicated telephone lines was laid by the General Post Office and Royal Corps of Signals, linking the AA sites, including many isolated searchlight positions.
On mobilisation in August 1939, 1st AA Division controlled 159 HAA guns, 96 searchlights, and a mixture of LAA guns (1 x 3-inch, 1 x 40mm Bofors and 52 light machine-guns (LMGs)). Most of the HAA guns were assigned to the IAZ, with one troop of 4 guns at RAF Fighter Command HQ at Stanmore and four more (16 guns) at airfields.
The London IAZ extended from Cheshunt and Dagenham in the east to Bexley and Mitcham in the south and to Richmond and Northolt in the west. The HAA positions were sited to produce an optimum density of fire of at least 16 guns engaging any one raid simultaneously. It had been intended that 26th AA Brigade would control the whole zone, but it proved too complex for one HQ, and in September 1939 it was divided among three: 26th AA Bde (34 sites disposed to north and east), 48th AA Bde (28 sites to south-east and south), and 49th AA Bde (12 sites to west). 26th AA Brigade still had the heaviest concentration of guns, mainly static 3.7-inch and 4.5-inch guns, with sites being increased from four to eight guns each. 48th AA Brigade had a mixture of 3.7 and 4.5-inch guns, half of the former being mobile. 49th AA Brigade had older 3-inch guns, but also controlled a higher proportion of LAA sites at Vital Points (VPs). Superimposed on the IAZ were the 73 searchlight sites controlled by 38th AA Bde.
Battle of Britain
On 5 June 1940, after the British Army had been evacuated from Dunkirk and the Battle of Britain was about to start, 1st AA Division comprised 45 4.5-inch, 39 3.7-inch and 26 3-inch HAA guns, with three 3-inch, 19 Bofors, three twin Vickers and 185 LMGs in the LAA role, together with 240 90 cm searchlights. On 11 July, the division's guns were disposed with 92 defending London, 28 at Slough, 4 at Hounslow, 4 at Stanmore, and 34 others dispersed to VPs.
While the Luftwaffe attacked RAF airfields, only the guns of 48th AA Bde in south-east London were engaged. On 1 September, over 200 aircraft attacked Maidstone, RAF Biggin Hill, RAF Kenley and Chatham: the guns of 1st and 6th AA Divisions broke up the attacks but Kenley and Biggin Hill were badly hit. The following day a raid up the Thames estuary reached the edge of the London IAZ and were engaged by 26th AA Bde. Between 11 and 15 September, massed raids approached London, but running battles with RAF fighters broke up most of the raids before they reached the IAZ, where they were engaged by 48th AA Bde.
By 30 September, when the Battle of Britain was effectively over and the Luftwaffe had switched to night raids over London (The Blitz), 1st AA Division had 233 HAA guns, 60 LAA guns, 161 LMGs and 242 searchlights covering the London IAZ, together with 36 HAA guns defending Slough, Langley, Weybridge and airfields.
In the absence of inland radar coverage, 1st AA Division's Chief Signals Officer, Lt-Col G.C. Wickens, devised a system of 14 fixed base-lines of sound locators to detect night raids approaching the IAZ. These were linked by automatic telephone equipment to the Brompton operations room, where the angular plots were resolved to indicate grid squares where the HAA guns in range could fire an unseen barrage. This 'Fixed Azimuth' system came into action in June 1940, in time for the opening of the night Blitz on London. It was later replaced as searchlight control (SLC) and gunlaying (GL) radar systems were introduced.
However, the performance of the AA defences in the early weeks of the Blitz was poor. AA Command moved 108 HAA guns to the IAZ from other divisions, and arranged 'fighter nights' when the guns remained silent and RAF night fighters were allowed to operate over London with the searchlights. GL radar, modern sound-locators and larger (150 cm) searchlights were introduced as rapidly as possible. From September 1940, rocket projectors (Z Batteries) were introduced, equipped with rocket projectiles, and by February 1941, SLC began to be issued. The number of raiders shot down steadily increased until mid-May 1941, when the Luftwaffe scaled down its attacks. During 1941 increasing numbers of women of the Auxiliary Territorial Service (ATS) took over roles in AA Command. Where they were integrated into units these were designated 'Mixed' ('M').
Towards the end of 1940, at the height of The Blitz, AA Command formed three AA Corps: 1st AA Division formed part of 1 AA Corps in Southern England.
Order of Battle 1941–42
From this time 1st AA Division's composition was as follows:
1st AA Division became independent, leaving 1st AA Corps and coming directly under AA Command, during April 1942.
1 AA Division, like the other AA Corps and Divisions, was disbanded and replaced on 1 October 1942 by a new AA Group structure. London was covered by 1 AA Group.
General Officers Commanding
The following officers commanded 1st AA Division: