73rd (Kent Fortress) Searchlight Regiment, Royal Artillery

90 cm Projector Anti-Aircraft, displayed at Fort Nelson, Portsmouth

The TA's AA units were mobilised on 23 September 1938 during the Munich Crisis, with units manning their emergency positions within 24 hours, even though many did not yet have their full complement of men or equipment. The emergency lasted three weeks, and they were stood down on 13 October.[8] In February 1939 the existing AA defences came under the control of a new Anti-Aircraft Command. In June, a partial mobilisation of TA units 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 and searchlight positions. On 24 August, ahead of the declaration of war, AA Command was fully mobilised at its war stations.[9][7]

• 322 AA Company: Horns Cross; mobilisation store at Kidbrooke
• 331 AA Company: Crown Inn, Laindon, Essex; mobilisation store at Warley, Essex
• 347 AA Company: Windmill Hotel, Kingshill, Kent; mobilisation store at Wainscott, Kent

The battalion formed part of 29th (East Anglian) Anti-Aircraft Brigade in 6th Anti-Aircraft Division, responsible for the air defence of the Thames Estuary and the adjacent Kent and Essex shores.[3][6][10]

In the Spring of 1940, 6 AA Division reorganised its growing AA defences. As a result, 73rd AA Bn and its S/L sites were transferred from 29th AA Bde to 56th Light AA Bde. This formation controlled the S/L sites and Light AA (LAA) guns in Kent, supporting the Heavy AA guns of the Thames South zone running from Dartford to Chatham and the RAF's Night fighters.[11]

Cap Badge of the Royal Artillery.

The Phoney War ended with the German invasion of France and the Low Countries on 10 May 1940. Home Forces became concerned about the threat from German paratroopers and AA Command's units were given anti-invasion roles. A plan to attach groups of riflemen from the infantry training centres to 6 AA Division's widely-spaced S/L sites foundered on the lack of men. Instead, the S/L detachments themselves 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. 73rd AA Battalion drew extra rifles and ammunition from Wainscott Ordnance Store.[11]

On 1 August 1940, the battalion, along with all other RE searchlight units, was transferred to the Royal Artillery (RA), becoming 73rd (Kent Fortress) Searchlight Regiment, and its AA companies were termed searchlight (S/L) batteries.[1][2][12][13][14]

Formation sign of 6 Anti-Aircraft Division, worn until September 1942.

The S/L layouts had been based on a spacing of 3500 yards, but due to equipment shortages this had been extended to 6000 yards by the time the Luftwaffe began its night Blitz in September 1940. In November, this was changed to clusters of three lights to improve illumination, but this meant that the clusters had to be spaced 10,400 yards apart. 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 Royal Air Force (RAF) Night fighters. Eventually, one light in each cluster was to be equipped with searchlight control (SLC) radar and act as 'master light', but the radar equipment was still in short supply.[15] 73rd S/L Regiment served throughout the Blitz.[16][17][18][19][20]

The regiment supplied a cadre of experienced officers and men to 236th S/L Training Rgt at Oswestry where it provided the basis for a new 533 S/L Bty formed on 14 November 1940. This battery later joined 87th S/L Rgt.[1]

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 inland to cooperate with night fighters.[21] On 23 January 1942, the regiment was joined by 508 S/L Bty from 29th (Kent) S/L Rgt, when the rest of that regiment moved from 56th LAA Bde to South West England.[1][22] There was another shake-up of AA Command at the beginning of October 1942, when the AA Divisions were replaced by AA Groups having a wider remit. 56th LAA Brigade and 73rd S/L Rgt were now in 2 AA Group, but 73rd S/L Regiment remained in Kent with 56th LAA Bde throughout the year.[23][24]

In February 1943, 73rd (Kent Fortress) S/L Rgt was transferred from 56th AA Bde to reinforce 27th AA Bde on the South Coast. 27th AA Brigade was dealing with 'hit-and-run' attacks by Luftwaffe fighter-bombers attacking coastal towns at low level in daylight, and the defensive armament of S/L positions was increased, with the existing Lewis guns being supplemented with twin Vickers K machine gun mountings and later twin 0.5-inch Browning machine guns on power mountings. On 10 April, 73rd S/L Rgt was replaced in this duty by 33rd (St Pancras) S/L Rgt and returned to 56th AA Bde.[25][26][27][28]

AA Command formation badge, worn from 1942.

By mid-1943, AA Command was being forced to release manpower for overseas service, particularly Operation Overlord (the planned Allied invasion of Normandy) and most S/L regiments lost one of their four batteries; 347 S/L Bty was disbanded on 5 July 1943.[1][29][30][31]

Soon after D Day, the Germans began launching V-1 flying bombs against London by day and night. The AA resources in SE England were strongly reinforced in Operation Diver, but the LAA batteries found these small, fast-moving targets hard to engage. Searchlight units used their SLC radar to help guide the LAA guns.[32] A lull in the V-1 attacks saw renewed pressure on AA Command to release men for 21st Army Group fighting in North West Europe, and 73rd (Kent Fortress) S/L Rgt was among the regiments that were lost, passing into suspended animation at Braunton in North Devon on 23 September 1944 and completing the process by 3 March 1945.[1][3][12][13][33]