In peacetime and during the wars the brigade was an integral part of the 54th (East Anglian) Infantry Division and contained mostly battalions of the Essex Regiment.

The more complete mobilisation scheme introduced by the Stanhope Memorandum of December 1888 saw all the Volunteer units assigned to garrisons or mobile brigades.

[1][5] He was followed by Colonel Harry Cooper, CMG, CBE, who had seen active service in Canada, Ashanti, Burma, Sudan and South Africa, and went on to serve at General Headquarters of the British Expeditionary Force (BEF) in France during the First World War.

[11] The East Anglian Division was a week into its fortnight's annual training at Clacton when the order to mobilise arrived on 4 August 1914.

The units immediately proceeded to their designated war stations defending the East Anglian coast, with 7th Essex at Felixstowe.

[14] The East Anglian division was employed on coast defence until May 1915, when it concentrated around St Albans to prepare for overseas service.

The four battalions adopted distinctive shapes for these patches:[17] 161st Brigade sailed from Devonport, Devon between 21 and 26 July 1915 and assembled at Mudros.

The rest of 54th Division landed at Suvla Bay on 10 August in a last attempt to restart the stalled Gallipoli Campaign, but was misused and stalemate ensued.

[20][21] The Essex battalions arrived still understrength, and armed with obsolete long Lee–Enfield rifles – many soldiers exchanged these for modern SMLE weapons picked up from casualties.

[22] On the afternoon of 14 August the brigade advanced over open ground to relieve the Norfolks and Suffolks after their disastrous attack.

[21][26] Throughout September and October 1915, 54th Division made preparations to complete the capture of Hill 60 sector, described by one of the officers as 'notoriously one of the most unpleasant spots on the peninsula'.

After a few days in the rest area, 54 Division marched down to the beach and embarked for Mudros, where the battalions reverted to their former brigades.

The Essex battalions were relieved from this duty on 4 March 1916 by the 2nd County of London Yeomanry and moved into the No 1 (Southern) Section of the Suez Canal Defences.

[10][29] The Brigade Machine Gun Company was formed at Shallufah on 22–23 April by taking two officers and the machine-gun (MG) detachment from each battalion.

On 5 August, supporting 52nd (Lowland) Division round Mount Rowston, the company took part in the decisive action of the battle, resisting a stiff attack in which it suffered several casualties, and won a number of gallantry awards.

[33][34] For the Second Battle of Gaza (17–19 April 1917) 1/7th Battalion was detached from 161st Brigade and was assigned to the Imperial Camel Corps (ICC), which was protecting the left flank of 54th Division.

[33][35] During the summer months 161st Brigade held the line without suffering serious casualties, and recovered its strength for the forthcoming Third Battle of Gaza (1–3 November 1917).

During the rapid pursuit after the fall of Gaza, 1/4th and 1/6th Essex assisted the ANZAC Mounted Division, while 1/5th and 1/7th were left marching in the rear.

The brigade formed up before dawn on 19 September, and attacked under the cover of an overhead barrage from the machine gun companies.

Preparations for demobilisation began, but civil unrest in Egypt meant that 161st Brigade was engaged in peacekeeping duties from March to May 1919.

[42] During the 1930s the air defences of the United Kingdom were strengthened, with a number of TA infantry battalions being converted to new roles: in 1935 the 7th Battalion, Essex Regiment was transferred to the Royal Artillery (RA) as 59th (The Essex Regiment) Anti-Aircraft Brigade, RA, (TA) and left 161st Brigade.

It then travelled on to Egypt, arriving in July, where it came under Middle East Forces, spending short periods under command of 4th Indian Infantry Division, XIII Corps, and British Eighth Army, while most of its units were stripped away.