The 6th AA Division was formed during 1939 to take responsibility for the air defence of the Thames Estuary, Essex and North Kent, with its HQ at Uxbridge, Middlesex.

[14][16] Forty-five 'vulnerable points' (VPs) in the divisional area were defended by LAA guns: these included Air Ministry Experimental Stations, fighter aerodromes, dockyards, oil depots, magazines, and factories.

[14] To deal with minelaying off East Anglia and Kent, the 6th AA Division organised a flotilla of three small Paddle steamers, each equipped with one Bofors gun and two S/Ls.

Their role was to patrol the channels off the coast to engage enemy minelaying aircraft and to report the position of mines to the Royal Navy or to detonate them if possible.

A plan to attach groups of riflemen from the infantry training centres to the 6th AA Division's widely spaced S/L sites foundered on the lack of men.

Instead the S/L detachments were given the responsibility for attacking parachutists before they could organise, and spare men at company HQs were formed into mobile columns using requisitioned civilian transport to hunt them down.

In July, the Luftwaffe switched back to heavy daylight raids against south coast ports and shipping: the guns at Dover were in action virtually every day.

Four days later a mass raid flew up the Thames Estuary to attack RAF Hornchurch and was engaged by the 28th and 37th AA Brigades in 'Thames North' and 'Thames South'.

[14][26] The peak intensity of the Battle of Britain came between 24 August and 15 September as the Luftwaffe put in its maximum effort to destroy Fighter Command.

In joint action with the fighters, the guns of the 1st and 6th AA Divisions broke up the attacks and shot down four aircraft, but the airfields at Kenley and Biggin Hill were badly hit.

On 7 September over 300 aircraft approached the Thames Estuary, where the 15th HAA batteries of the 28th and 37th AA Brigade split the formations up, although the Thameshaven oil wharves, Tilbury Docks, Woolwich and West Ham were badly hit.

One of the lessons of the Battle of Britain was that day bombers needed to fly in tight formation for mutual protection against fighters, but in doing so they were vulnerable to AA fire.

The opening salvo from a troop of four 3.7-inch guns of the 28th AA Brigade brought down the three leading aircraft and scattered the others in disorder, jettisoning their bombs as they escaped.

[27] The 6th AA Division's guns were again in prolonged action during the running battles of 15 September, when the Luftwaffe made its last and biggest attempt to gain air supremacy.

[14][26][28] Although there were severe night bombing raids against many industrial towns and cities of the UK during The Blitz, the main Luftwaffe effort was directed against London.

There were over 20 HAA sites planned for Thames North (37th AA Brigade ) from Dagenham to Thorpe Bay, of which only half were occupied in September 1940 with a mixture of 3.7-inch and 4.5-inch guns.

VPs requiring LAA defence included Crayford, Northfleet, Rochester and the Isle of Grain on the estuary together with the nearby RAF airfields at Biggin Hill and West Malling.

[36] During this period the division was composed as follows (temporary attachments omitted):[37][38][36] By December 1941, the 37th AA Brigade only had the 75th HAA Rgt under its command; it was then joined by: By May 1942, the 56th AA Brigade only had the 4th LAA and 73rd S/L under its command; it was then joined by: The increased sophistication of Operations Rooms and communications was reflected in the growth in support units, which attained the following organisation by May 1942:[36] The RAOC workshop companies became part of the new Royal Electrical and Mechanical Engineers (REME) during 1942.