When the air defences of Britain are considered, the work of day and night fighters of the Royal Air Force receives extensive coverage. However, the combination of searchlight units and anti-aircraft batteries were of great value in defeating enemy air attacks on Britain, particularly in the first 18 months of the war until radar-equipped night fighters became available in worthwhile numbers.

Like many other areas throughout Britain, the county saw both searchlights and anti-aircraft guns set up in the area. Combined searchlight and anti-aircraft batteries were established at Keith, near Humbie; Whitburgh. near Pathhead; and Frostineb, near Fala. Other searchlight positions were near Gifford, Haddington, Dirleton, Whitekirk, East Linton, Whittinghame and Garvald.

The 4/5th Battalion, Royal Scots played a major role in these defences, having become a Searchlight Regiment in 1938. The 405th Searchlight Company manned sites in East Lothian, with the Company Headquarters at Clerkington House, near Haddington; 407th Searchlight Company covered positions in the Musselburgh area and also Midlothian. The unit near Humbie took prisoner the airmen from the Heinkel He 111 which crashed nearby on 28 October 1939.

The main purpose of the unit was to illuminate enemy aircraft and in this role the Battalion had great success. One of the busiest nights was that of 13/14 March 1941. As German bombers flew towards Clydeside from the east coast, they were picked up by the searchlight units in East Lothian. The light at Pathhead had no less than 13 successful illuminations that night, although none of the anti-aircraft guns in the area were able to engage the bombers,. Needless to say, this proved extremely frustrating to the searchlight personnel!
Despite such problems on occasion, the searchlights played an important part in the destruction of several aircraft and as such were a vital component of the air defences of south-east Scotland.