117th Heavy Anti-Aircraft Regiment (117th HAA Rgt) was an air defence unit of Britain's Royal Artillery during World War II.

Regimental Headquarters (RHQ) was formed on 20 December 1940 at No 5 AA Practice Camp at Weybourne, Norfolk, to take command of 369, 370 and 371 HAA Batteries, which had been raised on 15 October 1940.

[1][2] Major R.A. Sparks, second-in-command of 99th (London Welsh) HAA Rgt, was promoted to Lieutenant-Colonel as commanding officer (CO) of the new regiment on 8 January 1941.

The handover occurred on 8 February, but 371 Bty temporarily remained at Scunthorpe in the Humber GDA under 39th AA Bde.

[5][6][7] 39th AA Brigade's operation order for 117th HAA Rgt's arrival commented that 'These batteries have had little training and have never practised unseen methods of fire', and arranged that the outgoing batteries of 91st HAA Rgt would temporarily leave experienced gun position officers (GPOs) and their assistants at the sites, together with gun No 1s, to train 117th's men.

[9][10][11] 371 HAA Battery rejoined the regiment at Sheffield on 20 February and RHQ remained with 62nd AA Bde through the summer of 1941.

Although much damage was caused in London, the rising efficiency of the HAA guns and radar made the enemy's losses unsustainable.

[18][19][20] The Baby Blitz notwithstanding, the threat from air attacks on the UK had diminished by early 1944 and AA Command was required to release manpower to the field armies, particularly for the forthcoming Allied invasion of Normandy (Operation Overlord).

A number of AA units in Air Defence of Great Britain lost one of their batteries, including 117th HAA Rgt.

In the event, the first of these did not arrive over England until a week after 'Overlord' began with the D Day landings, and AA units quickly deployed for Operation Diver.

On 16 July 1 AA Group was ordered to form a 'Diver Box' of gun defences across the Thames Estuary, forward of a line from Chelmsford in Essex to Chatham, Kent.

It was largely equipped with Mark IIC 3.7-inch HAA guns with No 10 Predictors and SCR-584 radar, and began using the proximity VT fuze with great success.

Meanwhile 21st Army Group fighting in North West Europe was suffering a severe manpower shortage, particularly among the infantry.