On 1 November 1938 the 6th Battalion was split into two battalions - 1/6th Battalion and 2/6th Battalion. The two new battalions changed their role from infantry to searchlights.

The 1/6th Battalion retained the old 6th Battalion HQ with 3 Companies at the Cedars, West Ham with a Company based at Chingford Drill Hall.

After mobilisation the battalion was deployed as operational to Wisbech with bases at nearby Narborough and Walpole Highway.

The HQ of the 2/6th Battalion was at Prittlewell. Training was completed  and the battalion were based at at Weybourne in Norfolk.

64th and 65th ( Essex Regiment ) Searchlight Regiments

On 1 August 1940 all searchlight units operated by Infantry, Royal Engineers and Royal Artillery were transferred to the Royal Artillery including the Essex pair where they were known as the 64th and 65th ( Essex Regiment ) Searchlight Regiments, Royal Artillery. The men now wore the uniform of the Royal Artillery but retained their Essex Regiment cap badges and buttons.

The 64th was now deployed to Billing, Northants with bases at Towcester, Ramsey Hunts and Thrapston where they were to remain until 1943 when they moved to Yorkshire with bases at York, Selby and Easingwold. In 1944 the 64th moved to Norfolk for a short time before being deployed at London to help deal with the flying bombs

The 65th served at Lincolnshire and the Humber mainly protecting the ports of Grimsby and Hull.

By 1944 the threat from German air raids had lessened and so both battalions were converted back to infantry battalions.

639th (Essex Regiment) Garrison Regiment and 607th (Essex Regiment) Garrison Regiment.

The 64th became the 639th (Essex Regiment) Garrison Regiment and the 65th became the 607th (Essex Regiment) Garrison Regiment.

The allies liberated Osnabuck in Germany in April 1945 with the newly formed 639th being responsible for garrisoning the town, guarding ammunition stores and camps for displaced refugees until 1946 when it was operationally suspended.

In May 1945,the 607th were stationed in Belgium near to Antwerp at Averbode, Kermpt, Lumen and Kirkoven mainly involved in garden the large oil/ petrol installations In Belgium after which they moved to Burg Leopold and then Minden in August 1945 before being disbanded in 1946.

599th ( Essex Regiment) HAA  and the 600th  (Essex Regiment) HAA

After the war with the re-organisation of the Territorial Army the 639th was reformed as  the 599th ( Essex Regiment) HAA  with a HQ at the Drill Hall Chingford and one battery at the old HQ at West Ham .

The 607th was reformed as the 600th  (Essex Regiment) HAA based at the Drill Hall, East Ham and now equipped with 3.7" mobile guns. A company was also established at Prittlewell the old HQ of the 2/6th battalion.