3rd Anti-Aircraft Division (United Kingdom)

3rd Anti-Aircraft Division
Active	1 September 1939 – 30 September 1942
Country	United Kingdom
Branch	Territorial Army
Type	Anti-Aircraft Division
Role	Air Defence
Part of	Anti-Aircraft Command (1939–40) 3 AA Corps (1940–42) 1 AA Corps (1942)
Engagements	The Blitz
Commanders
Notable commanders	Maj-Gen Lancelot Hickes Maj-Gen William Wyndham Green

The 3rd Anti-Aircraft Division was an air defence formation of the Territorial Army, part of the British Army, created in the period of tension before the outbreak of World War II. It defended Scotland and Northern Ireland during the early part of the war.

Large numbers of Territorial Army (TA) units were converted to anti-aircraft (AA) and searchlight roles in the Royal Artillery (RA) and Royal Engineers (RE) during the 1930s, and higher formations were required to control them. 3rd AA Division was the first division-level headquarters created de novo (earlier ones being converted infantry divisions). It was formed at Edinburgh on 1 September 1938 within Scottish Command, transferring to Anti-Aircraft Command when that formation was created on 1 April 1939. It was responsible for the AA defences of Scotland, including Northern Ireland and the Orkney and Shetland Defences (OSDEF). It operated with No 13 Group of RAF Fighter Command, covering Scotland and the North of England.

The composition of 3 AA Division on the outbreak of war was as follows:

Mobilisation in the last week of August 1939 was difficult for 3 AA Division, which had the task of moving troops, guns and stores by road and by sea to remote and inaccessible sites in Orkney to defend the fleet anchorage at Scapa Flow, which had high priority.

At this point the division had a strength of 111 HAA guns, while in the LAA role there were 18 3-inch, 5 2-pounder 'pom-pom' and 40 mm Bofors guns, and 340 light machine guns (LMGs), together with 159 searchlights. The HAA guns were deployed in the defended areas as follows:

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