It defended Scotland, Northern Ireland and North East England during the Blitz and the middle years of the Second World War.

[2][3][4][5] Continued expansion made this organisation unwieldy, so in November 1940 – during the Luftwaffe's nightly Blitz on London and other British cities – five further AA Divisions were organised, and all the divisions grouped under three corps headquarters directly subordinate to AA Command.

III AA Corps covered North Eastern England, Scotland and Northern Ireland, and by February 1941 comprised four division-level headquarters and 11 brigades.

[2][5][6][7] III AA Corps had the following organisation from February 1941:[8][9][10][11][12][13] Corps HQ: Edinburgh General Officer Commanding:[5][14] During its short existence, III AA Corps had to deal with the 1940–41 Blitz on industrial towns and cities such as Belfast, Clydebank, Greenock and Newcastle upon Tyne, as well as later raids on Middlesbrough and Sunderland.

The area covered by III AA Corps became the responsibility of two of the new groups: 6th Anti-Aircraft Group (North East England and Scotland) and 7th Anti-Aircraft Group (Northern Ireland); OSDEF remained directly subordinate to AA Command.