4th Anti-Aircraft Brigade (4 AA Bde) was an air defence formation of the British Army during World War II. It was formed just before the Battle of France to protect the British Expeditionary Force's bases. After the Dunkirk evacuation it was reformed in Egypt as a mobile formation with the Western Desert Force. It played a distinguished part in the Defence of Tobruk in 1941, but its headquarters was captured in the Fall of Tobruk the following year. It was reconstituted as a training formation in Persia and Iraq Command for the rest of the war.