The emergency lasted three weeks, and they were stood down on 13 October. In June 1939, as the international situation worsened, a partial mobilisation of the TA was begun in a process known as 'couverture', whereby each AA unit did a month's tour of duty in rotation to man selected AA gun and searchlight positions. On 24 August, ahead of the declaration of war, AA Command was fully mobilised at its war stations.  28 AA Battalion's company HQs were distributed as follows:  When war was declared on 3 September 1939, 28 AA Bn was still in 29 AA Bde, but this had been transferred to 6th AA Division which was formed in 1939 to take responsibility for air defence of the Thames Estuary, Essex and Kent. In common with other RE searchlight battalions, the unit was transferred to Royal Artillery in August 1940, becoming 28th (Essex) Searchlight Regiment RA (TA), and the companies were termed batteries. At this time, AA Command was heavily engaged in the Battle of Britain, in which 29 AA Bde was responsible for guarding Kent. This was soon followed by the night-bombing campaign of The Blitz, in which searchlights were a key element in the defences. As of 1 November 1941, the regimental and battery HQs were distributed as follows:  In November 1940, all S/Ls in 29 AA Bde's area, except the coastal sites, had been 'clustered' in threes at 10,400-yard intervals. The cluster system was an attempt to improve the chances of picking up enemy bombers and keeping them illuminated for engagement by AA guns or Night fighters. Eventually, one light in each cluster was to be equipped with searchlight control (SLC) radar and act as a 'master light', but the radar equipment was still in short supply. The regiment supplied a cadre of experienced officers and men to 231st S/L Training Rgt at Blandford Camp where it provided the basis for a new 546 S/L Bty formed on 16 January 1941. This battery later joined a newly-forming 90th S/L Rgt. By October 1941, the availability of SLC radar was sufficient to allow AA Command's S/Ls to be 'declustered' into single-light sites spaced at 10,400-yard intervals in 'Indicator Belts' along the coast and 'Killer Belts' at 6000-yard spacing to cooperate with the RAF's Night-fighters. 29th AA Brigade deployed 90 mm S/Ls in the indicator belt and 150 mm S/Ls in the killer belt, while a mixture of 90 mm and 120 mm lights were deployed in the Harwich Gun Defence Area, spaced at 10,400 yards in the inner zone and 6000 yards in the outer.