3rd Anti-Aircraft Brigade (3 AA Bde) was a Supplementary Reserve air defence formation of the British Army formed in Northern Ireland in 1938.

On the outbreak of the Second World War it saw active service with the British Expeditionary Force during the Battle of France and Operation Aerial.

During the 1930s the development of airpower led the United Kingdom to expand its anti-aircraft (AA) defences, a process that accelerated after the Munich Crisis of 1938.

3rd Anti-Aircraft Brigade formed on 7 December 1938 at Belfast to take command of the growing number of AA units in Northern Ireland.

The Territorial Army (TA) did not exist in Northern Ireland at that time so the part-time units in the Province were part of the Supplementary Reserve (SR) and were numbered in sequence after the Regulars.

The brigade formed part of 3rd AA Division, which was responsible for the defence of Scotland and Northern Ireland under Anti-Aircraft Command.

[14] In November 1939, however, 3 AA Bde HQ and some of its units crossed to France to defend the lines of communication of the British Expeditionary Force (BEF).

Part of 349 Coy landed there on 19 May and entrained for Le Havre, but returned to Cherbourg after a 900 miles (1,400 km) trip round France.

However, 2nd Panzer Division was already in Abbeville blocking the way, and the battery had to fight a rearguard action with enemy ground troops to get to the coast and make it back to Dunkirk.

Nightly air attacks on the Le Havre harbour area began in earnest on 3/4 June, with the guns in action for long periods.

[30][31][32] Similarly, on the night of 11/12 June 246 AA Bty disabled its static guns and boarded the Southern Railway ferry SS Brittany, which took the men to Cherbourg.

With great difficulty, the section got all the secret equipment aboard the SS Marslew which sailed on 18 June and docked at Falmouth the following day.

From Cherbourg, RHQ 79th (HY) AA Rgt and the two batteries without equipment were shunted by train between Nantes and Rennes before being evacuated from St Nazaire aboard SS Duchess of York and reaching Liverpool on 18 June.

247 Battery, operating directly under 3 AA Bde, deployed to defend Rennes and then moved to St Nazaire on 18 June, when it dumped its disabled guns in the dock and boarded SS Glenaffric and was evacuated to Plymouth.

The cluster system was an attempt to improve the chances of picking up enemy bombers and keeping them illuminated for engagement by AA guns or night-fighters.

Operating under the command of 4 AA Group in North-West England, it had the following composition:[1][78][79][80] (M) indicates a 'Mixed' unit, in which members of the Women's Royal Army Corps were integrated.