The Great War began in August 1914 and most of the men of the brigade immediately volunteered for Imperial Service overseas although they were not obliged to do so, as the Territorial Force was initially intended to act as a home defence force during wartime. The Territorial Force was, therefore, split into a 1st Line and a 2nd Line. The 1st Line was liable for service overseas and the 2nd Line was intended to perform a home defence role and to send drafts of replacements to the 1st Line units serving overseas. The West Lancashire Division and Liverpool Brigade formed a duplicate 2nd Line units, the 2nd West Lancashire Division and 2nd Liverpool Brigade. To distinguish the 1st Line battalions from the 2nd Line, they adopted the fractional '1/', for all 1st Line units, and '2/' for all 2nd Line. However, between November 1914 and March 1915, all the infantry battalions of the West Lancashire Division were sent overseas to France and Belgium to reinforce the British Expeditionary Forceon the Western Front which had suffered heavy casualties and was struggling to hold the line. As a result, the division was temporarily disbanded and the 1st Liverpool Brigade joined with its 2nd Line, now numbered as the 171st Brigade, and the division 57th Division. In early 1916 the West Lancashire Division was reformed, and now numbered as the 55th Division and the brigades were also numbered, the 1st Liverpool Brigade becoming 165th Brigade The brigade served with the 55th Division for the rest of the war on the Western Front at the Third Battle of Ypres, Battle of Cambrai and the Battle of Estaires in 1918.
The brigade was disbanded after the war in 1919 when the Territorial Force was disbanded. It was later renamed in 1920 as the Territorial Army. The brigade came into existence again as the 165th Infantry Brigade, again assigned to the 55th Division and again had the same four battalions of the King's Regiment. However, under the Geddes Axe, the 8th Battalion was disbanded on 31 March 1922 and were replaced in the brigade by the 10th Battalion, previously from the 166th Infantry Brigade. The composition of the brigade remained unchanged throughout most of the inter-war years. In the late 1930s, however, many infantry battalions of the Territorial Army were converted to new roles, mainly anti-aircraft or searchlight units. The 6th Battalion was transferred to the Royal Engineers and converted to 38th Anti-Aircraft Battalion, Royal Engineers, assigned to the 33rd Anti-Aircraft Group, 2nd Anti-Aircraft Division, serving alongside other units converted from infantry battalions. They replaced in the brigade by the 4th/5th Battalion, Cheshire Regiment. In 1938, the 10th Battalion was transferred to the Queen's Own Cameron Highlanders and was re-titled as the Liverpool Scottish but remained with the brigade. In the same year, when all infantry brigades of the British Army were reduced from four to three battalions, the 7th Battalion, King's was transferred to the Royal Tank Regiment and became 40th Royal Tank Regiment, assigned to 23rd Army Tank Brigade. When the 7th Battalion left to become 40th RTR they were replaced by 4th Battalion, South Lancashire Regiment, previously from 166th Infantry Brigade. Sometime in 1939, the brigade was redesignated 165th Infantry Brigade.
Second World War
The brigade again served in World War II with the 55th Division throughout the war and, in October 1941, no longer was an operational formation to be sent overseas. In January 1942 it was reduced to a Lower Establishment yet it was not reduced to a training division as most others were. In December 1943, with the division, it was sent to Northern Ireland and was raised to a Higher Establishment in May 1944, before returning to the United Kingdom in July. It served there until the war finally ended in 1945 and the division was disbanded in 1946 and was not reformed.
