 With the expansion of Britain's Anti-Aircraft (AA) defences during the late 1930s, new formations were created to command the growing number of Royal Artillery (RA) and Royal Engineers (RE) AA gun and searchlight units.42nd AA Brigade was raised on 1 October 1938 at Glasgow, and formed part of 3rd AA Division, which had been created a month earlier for the air defence of Scotland and Northern Ireland.42 AA Brigade's first commander was Brigadier W.M.M.O'D.