Shortly before World War II, it became a searchlight unit and defended the UK during the Blitz, remaining in the air defence role in the postwar Territorial Army.

By now, the Railway connection had disappeared, and the unit had adopted the scarlet coat, blue facings and cap badge of the Royal Fusiliers.

[2][3][4] The Stanhope Memorandum of December 1888 proposed a comprehensive Mobilisation Scheme for Volunteer units, which would assemble in their own brigades at key points in case of war.

It served with the regulars during the guerrilla phase of the war, involving long marches, including the 'Great De Wet Hunt', and then tedious garrison duty in the Blockhouse lines.

A small number of officers and men ruled medically unfit or who had not volunteered for overseas service were left at Hampstead Road to begin recruiting a reserve battalion.

The Gharwal Bde was held up, except for the 2/8th Gurkha Rifles, but the brigade reserves (including 1/3rd Londons) were unable to exploit this fleeting success because the communication trenches to the front were knee-deep in mud.

[22][23][24][40][51][52] After the reformed division had shaken down, on 4 May, 167th Brigade took over part of the line facing the Gommecourt Salient, where it was due to attack in the forthcoming Battle of the Somme.

[53][54] Another round of intense work in preparing trenches, roads and dumps in June left the battalion exhausted and having suffered numerous casualties.

[55] 167th Brigade held the line in late June while the rest of the division practised the assault they were to make on Z Day (which was delayed by weather to 1 July).

[56] On the night of 29 June, 1/3rd Bn sent out a 20-man raiding party to a suspected machine gun post at Point 94, the junction of two German trenches codenamed 'Fir' and 'Firm'.

After crawling across 300 yards of No man's land through heaps of barbed wire, the patrol surprised a German working party and after a violent fight returned with a prisoner.

[67] In March 1917, the 56th Division was preparing to attack as part of the forthcoming Battle of Arras when patrols discovered that the Germans in front had disappeared – the beginning of their retreat to the Hindenburg Line.

The 2/3rd Londons were the worst hit of any unit: 50 men drowned and another 30 were evacuated with frostbite, leaving the battalion with an effective strength of just six officers and 50 other ranks.

[2][22][33][90][91] At the time of the renumbering, the 58th Division was carrying out coast defence duties in East Anglia, but on 10 July 1916 it concentrated at Sutton Veny for final training on Salisbury Plain.

[99][100][101] On 15 June, 173rd Bde attacked a section of the Hindenburg Line from 'The Knuckle' to 'The Hump', supported by the full artillery of V Corps and 7th, 58th (2/1st London) and 62nd (2nd West Riding) Divisions.

The platoon's objective was thus turned to this strongpoint, but this was found to have been abandoned, so the whole position was in British hands and was successfully held against fierce counter-attacks during the evening.

The battalion was then forced to jump off at 05.30 on 26 October from a line of flooded craters under enemy shellfire and struggle forward behind a weak barrage that advanced too quickly.

The exhausted men, with hardly a rifle able to fire because of the mud, got no closer than 250 yards from their objective at Spider Crossroads before being pushed back to their start line by a counter-attack at 07.20.

[117][118][119] The mixed force under 173rd Bde held out on the fourth day of the battle until the afternoon, when they made a planned withdrawal, and by 16.30 had retired across the Oise to join the rest of 58th Division.

The attack was then slowed by stubborn resistance and open flanks but at the end of the day the brigade made good its final objective overlooking the River Tortille and the Canal du Nord.

After a short period of training, the brigade made a more deliberate attack on 18 September supported by tanks and succeeded in taking Épehy and Pezières, 3rd Londons dealing with the strongpoint of Fisher's Keep.

[2] The following officers commanded 3rd (Reserve) Bn: In June 1915 the 'Home Service-only' and unfit men of the TF were formed into Provisional units for home defence.

[186] The regiment supplied a cadre of experienced officers and men to 233rd S/L Training Rgt at Saighton Camp where it provided the basis for a new 527 S/L Bty formed on 14 November 1940.

[174][187] Otherwise the regiment's organisation and subordination remained unchanged[188][189] until 20 December 1942, when 354 S/L Bty, a mobile S/L unit stationed at Peterborough, was re-regimented from 39th (Lancashire Fusiliers) S/L Rgt to 69th (3rd Londons) and moved to Old Buckenham in Norfolk.

[174][196][197] By early 1944, AA Command was forced to release further manpower for Operation Overlord (the Allied invasion of Normandy) and most S/L regiments lost one of their four batteries: 458 S/L Bty and the E Troops of 354 and 456 S/L Btys from 69th (3rd London) S/L Rgt all began disbanding 25 February, and the process was complete by 24 March.

[174][198][199] The regiment remained in the West Country, 354 S/L Bty moving to Castle Cary, Somerset, in February 1944, and then to Sturminster Marshall, Dorset, in August.

The AA resources in SE England were strongly reinforced in Operation Diver, the S/L belt being thickened up both to cooperate with RAF Night fighters and to use their S/L Control (SLC or 'Elsie') radar to guide LAA guns.

Once 21st Army Group overran the V-1 launching sites in northern France, the Luftwaffe took to air-launching V-1s from bombers over the North Sea, a tactic that resulted in further redeployment of AA Command's resources.

On 3 April 1945 563 LAA Trp was reconstituted with the assistance of some personnel from the battery, which itself began to disband at the RA Depot, Woolwich, on 8 May 1945, completing the process on 28 May.

[219] The 3rd London Regiment was awarded the following Battle honours:[3][7] South Africa, 1900–02 Neuve Chapelle, Aubers, Festubert, 1915, Somme, 1916, '18, Albert, 1916, '18, Ginchy, Flers-Courcelette, Morval, Le Transloy, Arras, 1917, Scarpe, 1917, Bullecourt, Ypres, 1917 Langemarck, 1917, Menin Road, Polygon Wood, Passchendaele, Cambrai, 1917, St Quentin, Bapaume, 1918, Villers Bretonneux, Amiens, Hindenburg Line, Épehy, Pursuit to Mons, France and Flanders 1915–18, Gallipoli 1915–16, Egypt, 1915–16.