58th (Middlesex) Searchlight Regiment, Royal Artillery was an air defence unit of Britain's Territorial Army (TA) raised just before World War II.

It defended the East Midlands of England during The Blitz, and later served as infantry in North West Europe at the end of the war, converting to the anti-aircraft (AA) artillery role postwar.

This searchlight unit was formed as part of the doubling in size of the TA at the time of the Munich Crisis in late 1938.

[16] The regiment also 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 539 S/L Bty formed on 12 December 1940.

100 AA Bde was one of the formations slated to participate in Operation Overlord (the Allied invasion of Normandy planned for 1944) and shortly afterwards the battery became formally independent of 58 S/L regiment.

[1] Soon after D Day in June 1944 the bombardment of London by German V-1 flying bombs began, and AA Command was engaged in the efforts to combat them (Operation Diver).

[21][22] The most severe phase of V1 attacks on the UK ended in September 1944 after the launching sites were overrun by the advance of 21st Army Group along the coast of France and Belgium.

[21][23] By the end of 1944, the German Luftwaffe was suffering from such shortages of pilots, aircraft and fuel that serious aerial attacks on the United Kingdom could be discounted and the War Office began reorganising surplus anti-aircraft regiments in the UK into infantry battalions for duties in the rear areas.

)[1][7][10][11][12][25] Meanwhile, 21st Army Group fighting in North West Europe was suffering a severe manpower shortage, particularly among the infantry.