It helped to defend the naval base of Portland Harbour during World War I and provided a detachment to serve with the British Expeditionary Force on the Western Front.

[3][4][5] The Dorsetshire unit was an Electric Lights (EL) Company based at the Sidney Groves Memorial Hall on North Quay, Weymouth, but is also recorded as having used the Old Drill Hall at Easton, in Easton Lane on the Isle of Portland (now the Portland Sculpture & Quarry Trust), which it shared with No 3 Company of the Dorsetshire Royal Garrison Artillery.

The Portland defence works were completed by November 1914, and the men underwent a month of strenuous training, including heavy bridge building and constructing trenches at night.

It then embarked aboard the SS Blackwell and arrived at Le Havre on 20 January 1915 to join the British Expeditionary Force (BEF) on the Western Front.

[18][25] The Wiltshire Fortress Engineers was not only a source of RE officers, but some of its men were commissioned as infantry officers in the Wiltshire Regiment[26] Reinforced, 565th (Wilts) Company spent the autumn and winter of 1915–16 building a new mill at Steenwerck and a hospital nearby at Trois Ambres, as well as working on roads, light railways and water supplies.

The Battle of the Somme opened on 1 July 1916 and shortly afterwards 565th (Wilts) Co was moved into the area to camp at Bronfay Farm and work on water supplies in the Carnoy Valley.

[27][28] The Third Ypres Offensive was about to begin, and Fourth Army HQ was switched to Dunkirk to command a thrust up the coast to meet the expected breakthrough in Flanders.

The company was put to work filling mine craters where the Hindenburg defences crossed the Bapaume–Cambrai road between the Canal du Nord and Graincourt.

After the German counter-attack, Company HQ was moved back to Ervillers, where the men worked in the forward areas on water supplies and building camps.

When the German offensive ran out of steam, the company was put to building a new defence line between Adinfer Wood and Fonquevillers on the old Somme battlefield.

[30] The Allied counter-offensive (the Hundred Days Offensive) began in August 1918, and 565th (Wilts) Co followed the advance, opening up new water points, including an important one at Douchy.

On 12 September the company reached Ruyaulcourt where it was given the task of constructing a 300 feet (91 m) ramp down the face of a retaining wall into the dry Canal du Nord suitable for traffic up to 6-inch guns.

It was back at the Canal du Nord on 27 September with VI Corps Troops RE,[31] where it was joined by the New Zealand Tunnelling Company.

It took 80 three-ton lorry loads to bring up the material, and the total time to unload and erect the bridge was 104 hours.

[30] As the Allied advance continued, the company was sent to Raches, where it worked on repairing heavy bridges in the Douai area, as part of First Army Troops RE,[33] though a lack of materials made progress slow.

[38][39] In 1934 the company carried out its annual training at the RE barracks at Gosport,[40] and the Parkstone Section practised anti-aircraft (AA) searchlight defence at Rossmore Plateau every week, usually watched by a large crowd.

[38][42] As the international situation worsened, key personnel of the unit were called up on 22 August, and the TA was fully mobilised two days later.

In the first weeks of the Phoney War the CD light installations at Portland and the naval training establishment HMS Osprey were put into service, despite a lack of stores and a serious fire in the Nothe generator room on 10 September that burnt out the switchboard and cables.

[44] After the British Expeditionary Force had been evacuated from Dunkirk, there were intense air battles over the English Channel, and Portland was heavily bombed on 4 July.

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 Night fighters.

Although the S/Ls and AA LMGs were busy, they achieved few illuminations and the noise drowned the sound locators, while telephone communication to the GOR broke down.

Further heavy raids over the next two nights repeated the destructive process on Devonport, including setting alight the oil storage tanks at Torpoint.

[49][45][60] Anti-Aircraft Command was suffering a manpower shortage and had begun to convert surplus S/L units to other roles such as light AA (LAA) guns.

As part of the reorganisation into indicator and gun zones, 82nd S/L Rgt's batteries were relieved in November and ordered to join other regiments; 483 S/L Bty even had a farewell parade.

[63][64][65][66] On 4 June 1943, RHQ moved from Oare to RAF Coltishall in Norfolk under 41 AA Bde and the batteries relieved those of 69th (3rd City of London) S/L Rgt.

[66][67][68] By early 1944 AA Command was being forced to make manpower cuts, releasing men to 21st Army Group for Operation Overlord, the planned Allied invasion of Normandy.

After this the regiment's strength was 37 officers, about 1245 other ranks, 87 women of the Auxiliary Territorial Service and 78 members of the Army Catering Corps (ACC).

The guns were emplaced on temporary 'Pile platforms' named after the Commander-in-Chief of AA Command, Gen Sir Frederick 'Tim' Pile.

[45][68][71][72][73] The War Office had warned in June 1944 that AA Command would have to release further manpower to provide reinforcements to 21st Army Group fighting in North West Europe.

Warner who on 21 February 1944 risked their lives in a fruitless attempt to rescue the crews of two Flying Fortresses that had collided and crashed in flames near their post.