 In 1938, when British infantry brigades were reduced from four to three battalions, the 6th Battalion, Gloucestershire Regiment was transferred to the Royal Tank Regiment, converting into an armoured role as 44th Battalion, Royal Tank Regiment (44 RTR), later becoming part of 21st Army Tank Brigade.In 1939 the brigade was redesignated the 145th Infantry Brigade.The Second World War began on 3 September 1939, although the division had been mobilised two days earlier, along with the rest of the Territorial Army due to the German invasion of Poland.