The regiment continued to serve in AA Command as part of 34 AA Bde, but was simultaneously part of  the War Office (WO) Reserve, organised as a mobile unit with all the necessary ancillary units:
RHQ
3 HAA Bty
12 HAA Bty
15 HAA Bty
6 HAA Rgt Signals Section, RCS
6 HAA Rgt Section, Royal Army Service Corps
6 HAA Rgt Workshop, Royal Army Ordnance Corps
Mobilisation exercises (codenamed 'Chestnut') were held in March and April to reconnoitre redeployment to Banbury, Oxford and Didcot to provide AA defence of defiles for the field army.
Also in March, 15 HAA Bty shifted four guns from Penn Common to a site south of Birmingham, and 12 HAA Bty deployed to new sites near Coventry.
There was a heavy raid on Birmingham and Coventry on 9/10 April, when 12 HAA Bty scored damaging hits on two aircraft.
There was another Chestnut exercise in May, when the redeployments to Oxfordshire were carried out for practice, before the guns returned to the Midlands.
Some of the guns were away on another exercise when Birmingham was attacked on 16/17 May; however 12 HAA Bty appeared to damage the formation leader, and the bombs were scattered to some extent.
By now the guns were being regularly switched between sites to confuse the Luftwaffe.
Longer distance mobile exercises (named 'Bertram Mills' schemes after the travelling circus) were carried out by batteries to Yorkshire, and Sussex, and sites were temporarily manned by 181/65 HAA Bty and 198 HAA Bty of 67th (York and Lancaster Regiment) HAA Rgt while 6th HAA Rgt's gunners went to practice ranges in Wales.

Lieutenant-Colonel G.W.G. Baass (who changed his surname to Baillie later that year) became CO on 15 June 1941.

In September, the regiment was ordered to prepare for embarkation for the Middle East.
It left AA Command and was relieved at its gunsites by 71st (Forth) HAA Rgt and concentrated at Bulford Camp on Salisbury Plain before proceeding to Liverpool for embarkation.
On 14 November 1941 the regiment sailed aboard the Monarch of Bermuda in Convoy WS12 bound for Iraq to join the build-up of AA defences for the oil terminal at Basra.

However, on 8 December, while the convoy was at Durban, the Japanese invaded Malaya shortly before attacking Pearl Harbor.
On 11 December the convoy was split, and the part containing 6th HAA Rgt (now aboard HM Transport Aorangi) was diverted to Singapore, arriving on 13 January 1942.
Several of the ships carrying equipment and vehicles had continued to Basra, but the gunners manned existing gunsites around Singapore island.
The regiment continued to serve in AA Command as part of 34 AA Bde, but was simultaneously part of  the War Office (WO) Reserve, organised as a mobile unit with all the necessary ancillary units:
RHQ
3 HAA Bty
12 HAA Bty
15 HAA Bty
6 HAA Rgt Signals Section, RCS
6 HAA Rgt Section, Royal Army Service Corps
6 HAA Rgt Workshop, Royal Army Ordnance Corps
Mobilisation exercises (codenamed 'Chestnut') were held in March and April to reconnoitre redeployment to Banbury, Oxford and Didcot to provide AA defence of defiles for the field army. Also in March, 15 HAA Bty shifted four guns from Penn Common to a site south of Birmingham, and 12 HAA Bty deployed to new sites near Coventry. There was a heavy raid on Birmingham and Coventry on 9/10 April, when 12 HAA Bty scored damaging hits on two aircraft. There was another Chestnut exercise in May, when the redeployments to Oxfordshire were carried out for practice, before the guns returned to the Midlands. Some of the guns were away on another exercise when Birmingham was attacked on 16/17 May; however 12 HAA Bty appeared to damage the formation leader, and the bombs were scattered to some extent. By now the guns were being regularly switched between sites to confuse the Luftwaffe. Longer distance mobile exercises (named 'Bertram Mills' schemes after the travelling circus) were carried out by batteries to Yorkshire, and Sussex, and sites were temporarily manned by 181/65 HAA Bty and 198 HAA Bty of 67th (York and Lancaster Regiment) HAA Rgt while 6th HAA Rgt's gunners went to practice ranges in Wales.
Lieutenant-Colonel G.W.G. Baass (who changed his surname to Baillie later that year) became CO on 15 June 1941.
In September, the regiment was ordered to prepare for embarkation for the Middle East. It left AA Command and was relieved at its gunsites by 71st (Forth) HAA Rgt and concentrated at Bulford Camp on Salisbury Plain before proceeding to Liverpool for embarkation. On 14 November 1941 the regiment sailed aboard the Monarch of Bermuda in Convoy WS12 bound for Iraq to join the build-up of AA defences for the oil terminal at Basra.
However, on 8 December, while the convoy was at Durban, the Japanese invaded Malaya shortly before attacking Pearl Harbor. On 11 December the convoy was split, and the part containing 6th HAA Rgt (now aboard HM Transport Aorangi) was diverted to Singapore, arriving on 13 January 1942. Several of the ships carrying equipment and vehicles had continued to Basra, but the gunners manned existing gunsites around Singapore island.
6th Heavy Anti-Aircraft Regiment, Royal Artillery