The 113th Heavy Anti-Aircraft Regiment (113th HAA Rgt) was an air defence unit of the British Army's Royal Artillery during World War II.

It saw action during The Blitz, landed in Normandy on D-Day and served throughout the subsequent campaign in North West Europe, operating as medium artillery in the Battle of the Scheldt, Unusually, its AA guns were successfully used to destroy enemy submarines in the closing stages of the war.

Regimental Headquarters (RHQ) was formed on 25 November 1940 at No 3 AA Practice Camp at Tŷ Croes on Anglesey to take command of 359, 362 and 366 HAA Batteries, which had been raised on 21 September 1940.

The newly formed 391 HAA Bty joined the regiment from No 2 AA Practice Camp at Burrow Head and took over sites round Derby in February.

[15] RHQ was established at Poolewe, and there were gun sites at Kyle of Lochalsh, Oban, Fort William and Balmacara.

362 Battery was detached to the London Inner Artillery Zone in October, manning sites at Walthamstow and Barnes, and then at Bedfont and Yeading in Middlesex, where it saw action against night intruders.

[16] At the beginning of 1944 the regiment moved its base to Southend-on-Sea, while parties again visited Otterburn and Clacton-on-Sea for firing practice, and took part in beach exercises at Inverary and Hayling Island.

113th HAA Regiment was assigned to the AA Assault Group scheduled to land on D-Day itself, on Jig and King sectors.

Light AA (LAA) defence was emphasised at the start of the operation, since low-level attack by Luftwaffe aircraft was considered the most likely threat, so the HAA guns would only begin to land on the second tide:[21][22][23][24][25][26] AA Assault Group In the event, there were delays in landing, so 120th LAA Rgt acted as infantry, clearing enemy positions while awaiting the arrival of their guns.

76th AA Bde planned to have put three HAA troops (12 x 3.7-inch guns) ashore by nightfall on D-Day, but in practice, this proved too ambitious.

RHQ of 113rd HAA Rgt landed at Le Hamel at 15.00 on the second tide and set up the tactical HQ, but none of its own guns appeared.

On 10 June the regiment collected two captured German 88mm flak guns and proposed to use them in the anti-tank role if required.

[22] 21st Army Group broke out from the Normandy beachhead at the end of August and began to pursue the defeated German troops across Northern France.

The batteries crossed the Bailey bridge at Elbeuf the following day and the regiment was in position at Bovelles on 3 September, with 362 Bty at Dieppe.

[30] On the night of 30 October it was reported that the Germans were withdrawing from the south side of the Scheldt by sea, and 362 Bty was ordered to fire airburst high explosive shells over the evacuations.

Finally, on 16 November, the batteries were ordered to return to Breskens on the south bank and be ferried across to Walcheren by the only LCT available.

[21][22][33] On 1 January 1945, the Luftwaffe launched Operation Bodenplatte: daylight attacks against Allied airfields in support of the Ardennes offensive.

On 22 February, gun position H71 (B Troop at Flushing) engaged one of these submarines with 22 rounds and destroyed it, just 20 minutes before a large convoy passed on its way to Antwerp.

[33][35][38] However, as the war in Europe drew to its close and the remnant of the Luftwaffe was powerless, the AA commitments could be reduced and troops redeployed.

The regiment was relieved from its positions on the Scheldt by 146th HAA Rgt and returned to Belgium, then on 18 April it was informed that it was to be disbanded.