The unit's origin lay in two independent AA Companies of the Royal Engineers (RE) formed in Aberdeen and Dundee in 1935 and equipped with searchlights. During the expansion of TA air defence units in 1938, the two were combined into a new 51st (Highland) AA Battalion, RE and a third company raised, giving the battalion the following organisation:HQ Company at Drill Hall, Bell St, Dundee
319 (City of Aberdeen) AA Company, Fonthill Barracks, Aberdeen
320 (City of Dundee) AA Company, Drill Hall, Bell St, Dundee
404 AA Company, Cowdenbeath
Major W.C.G. Black, MC, TD, officer commanding 20th (Fife & Forfar Yeomanry) Armoured Car Company, was promoted to lieutenant-colonel to command the new battalion on 12 October 1938.
In February 1939 the TA's AA units came under the control of a new Anti-Aircraft Command.
In June 1939 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. At this time, 51st AA Bn was part of 52nd Light Anti-Aircraft Brigade, a new formation being organised at Stirling with responsibility for searchlight provision within 3rd AA Division covering Scotland.
In February 1940, the regiment provided a cadre to help form a new 474 S/L Bty in 5th AA Division.
In August 1940 the RE searchlight battalions were transferred to the Royal Artillery (RA), and the unit was redesignated 51st (Highland) Searchlight Regiment, RA (TA). It remained with 52 AA Bde in 3 AA Division throughout the Battle of Britain and The Blitz (when Clydebank was badly hit).
In February 1942, the regiment was converted to the Light Anti-Aircraft (LAA) artillery role as 124 (Highland) Light Anti-Aircraft Regiment, RA (TA). The regiment's batteries became 404, 411 and 412 LAA Btys, and it was joined by 413 LAA Bty (previously 547 S/L Bty of 54th S/L Rgt). 413 LAA Bty was sent to 237th LAA Training Rgt at Holywood in Northern Ireland.
During May 1942, 124th LAA Rgt completed its re-equipment and training, and joined 30th (Northumbrian) AA Bde, covering Tyneside and Sunderland in 7th AA Division. 413 LAA Battery, for example, was sent to Seaham Holiday Camp, from where it took over operational sites in the Sunderland area and established its Battery HQ at Whitburn Hall, Whitburn. However, in September 1942, 413 LAA Bty left 124th LAA Rgt to join 143rd LAA Rgt in Essex, while the rest of the regiment moved to 47th AA Bde at Southampton.
By March 1943, the regiment had moved again, to 5 AA Bde in the Gloucester area, but had left AA Command by August 1943 and joined Second Army forming in England for Operation Overlord.
LAA regiments at this time comprised three batteries of three troops, each equipped with six towed Bofors 40 mm guns using 'Stiffkey Stick' sights. As a mobile unit, 124th LAA would also have had a Royal Electrical And Mechanical Engineers (REME) workshop and a detachment of the Royal Corps of Signals.
124 LAA Regiment went to Normandy in late August 1944 as part of 75th Anti-Aircraft Brigade, which immediately took over AA defence for the Caen area, including the Caen Canal and River Orne bridges. Two weeks later, Canadian troops captured Ostend, and 124 LAA Rgt with the rest of 75 AA Bde moved up the coast to defend it. In November it moved again, to guard the Scheldt estuary, and when the war ended the bulk of 124 LAA Rgt was on the south bank of the Scheldt under 75 AA Bde, with 411 Bty detached to the north bank under 76th AA Bde.
On 9 January 1945, four Bofors of 411 LAA Bty hit and sank a German Biber midget submarine operating off South Beveland. The regiment also manned the Bofors guns on two Landing Craft Flak operating in the estuary under with searchlights provided by 1st S/L Rgt. The battery remained with 76 AA Bde in the final weeks of the war.
After VE Day, the whole of 124 LAA Rgt came under command of 76 AA Bde as it moved into Germany to garrison the Dortmund–Bochum area under I Corps. After 76 AA Bde completed its disbandment in the first two weeks of April 1946, 124 LAA Rgt stayed on as part of British Army of the Rhine, but was placed in suspended animation later in the year.
When the TA was reconstituted in 1947, the regiment was reformed as 586 (Highland) LAA Regiment, RA, with HQ at Dundee and forming part of 78th AA Bde (the former 52 AA Bde) based in Perth.
In March 1949, the regiment was redesignated again, as 586 (Highland) LAA/Searchlight Regiment, RA.
When Anti-Aircraft Command was disbanded in March 1955, 586 Rgt was absorbed into 276th (Highland) Field Regiment, RA.
Honorary Capt C.A. Carlow, a retired Volunteer officer, was appointed Honorary Colonel of the battalion on 12 October 1938.
124 LAA Regiment wore a regimental shoulder flash consisting of a Scottish saltire in the RE colours of blue on red.