[2][3][4] 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 (the 2nd AA Division was formed in 1936 to cover the rest of the country).

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.

[10] 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'.

Crossman, DSO, MC HQ: Hillingdon House, RAF Uxbridge In August 1940 the RE 'Anti-Aircraft' (searchlight) battalions became regiments of the RA.

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.

[17] 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.

The 49th AA Brigade had older 3-inch guns, but also controlled a higher proportion of LAA sites at Vital Points (VPs).

[18] On 5 June 1940, after the British Army had been evacuated from Dunkirk and the Battle of Britain was about to start, the 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.

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.