During the period of international tension in 1938, the TA was rapidly expanded in size, particularly for the Anti-Aircraft (AA) role.
Much of this expansion was achieved by converting and/or expanding existing units.
In the case of 86th (East Anglian) (Herts Yeomanry) Field Brigade, Royal Artillery, partly descended from the old Hertfordshire Yeomanry cavalry, this was done by expanding 343 (Watford) Field Battery into a complete new AA brigade.
Orders were issued by the Army Council in July 1938 and the new unit came into existence on 1 November with the following organisation (the traditional term 'brigade' for a Lieutenant-Colonel's command in the Royal Artillery (RA) being superseded by 'regiment' on 1 January 1939, and the 'Hertfordshire Yeomanry' subtitle being granted in July 1939):
79th (Hertfordshire Yeomanry) Anti-Aircraft Regiment, RA
Regimental HQ (RHQ) at Clarendon Hall, Watford
246 (1st Watford) Anti-Aircraft Battery – 2 x QF 3-inch 20 cwt semi-mobile guns
247 (2nd Watford) Anti-Aircraft Battery – 2 x 3-inch semi-mobile guns
248 (Welwyn) Anti-Aircraft Battery at Lemsford Lane, Welwyn Garden City – due to receive QF 3.7-inch AA guns
2nd Hertfordshire Company of the Bedfordshire and Hertfordshire Unit, Auxiliary Territorial Service (ATS), was also based at Watford and affiliated to 79th (HY) AA Rgt.
Under the command of Jean Knox (later director of the ATS) it provided support staff in the early days.

86th Field Brigade had retained the Hertfordshire Yeomanry badge of the Hart (deer) as a collar badge worn in addition to the RA's 'gun' cap badge, and later it replaced the gun badge on side caps and berets; this was continued by the new unit even though 343 Field Bty was strictly descended from 4th East Anglian Brigade, Royal Field Artillery, and not the Yeomanry.

Major Thomas Bazley Green, TD, officer commanding (OC) 341 (St Albans) Field Bty, was promoted to Lt-Col to raise and command the new regiment.
Other officers were drawn from 86th Field Rgt and other TA units including Stockbrokers serving in the ranks of the 54th (City of London) AA Rgt.
During the period of international tension in 1938, the TA was rapidly expanded in size, particularly for the Anti-Aircraft (AA) role. Much of this expansion was achieved by converting and/or expanding existing units. In the case of 86th (East Anglian) (Herts Yeomanry) Field Brigade, Royal Artillery, partly descended from the old Hertfordshire Yeomanry cavalry, this was done by expanding 343 (Watford) Field Battery into a complete new AA brigade. Orders were issued by the Army Council in July 1938 and the new unit came into existence on 1 November with the following organisation (the traditional term 'brigade' for a Lieutenant-Colonel's command in the Royal Artillery (RA) being superseded by 'regiment' on 1 January 1939, and the 'Hertfordshire Yeomanry' subtitle being granted in July 1939):
79th (Hertfordshire Yeomanry) Anti-Aircraft Regiment, RA
Regimental HQ (RHQ) at Clarendon Hall, Watford
246 (1st Watford) Anti-Aircraft Battery – 2 x QF 3-inch 20 cwt semi-mobile guns
247 (2nd Watford) Anti-Aircraft Battery – 2 x 3-inch semi-mobile guns
248 (Welwyn) Anti-Aircraft Battery at Lemsford Lane, Welwyn Garden City – due to receive QF 3.7-inch AA guns
2nd Hertfordshire Company of the Bedfordshire and Hertfordshire Unit, Auxiliary Territorial Service (ATS), was also based at Watford and affiliated to 79th (HY) AA Rgt. Under the command of Jean Knox (later director of the ATS) it provided support staff in the early days.
86th Field Brigade had retained the Hertfordshire Yeomanry badge of the Hart (deer) as a collar badge worn in addition to the RA's 'gun' cap badge, and later it replaced the gun badge on side caps and berets; this was continued by the new unit even though 343 Field Bty was strictly descended from 4th East Anglian Brigade, Royal Field Artillery, and not the Yeomanry.
Major Thomas Bazley Green, TD, officer commanding (OC) 341 (St Albans) Field Bty, was promoted to Lt-Col to raise and command the new regiment. Other officers were drawn from 86th Field Rgt and other TA units including Stockbrokers serving in the ranks of the 54th (City of London) AA Rgt.
79th (Hertfordshire Yeomanry) Heavy Anti-Aircraft Regiment, Royal Artillery