By 1939 it became clear that a new European war was likely to break out and, as a direct result of the German invasion of Czechoslovakia on 15 March, the doubling of the Territorial Army was authorised, with each unit and formation forming a duplicate. Consequently, the 8th Battalion, Royal Northumberland Fusiliers was formed as a duplicate of the 4th Battalion on 18 June 1939 organized as a motorcycle battalion.
On 2 October 1939, the battalion was assigned to the 23rd Division. The division was sent to France on 22 April 1940, on labour and training duties, without any of its artillery or the bulk of its signals and administration units. On 20 May 1940, the division suffered heavy casualties trying to delay the German advance at Arras and had to be evacuated at Dunkirk. On its return to the United Kingdom the 23rd Division was disbanded due to the heavy losses it had suffered and the two infantry brigades were sent to other divisions. After Dunkirk, the battalion left the 23rd Division on 29 June 1940. It was under command of Home Forces until November 1940 when it joined the 3rd Infantry Division, a Regular Army formation, as a motorcycle battalion. The battalion was only of only two Territorial Army units in the division, the other being 76th Field Regiment, Royal Artillery. On 30 April 1941 it was transferred to the Reconnaissance Corps and redesignated as 3rd Battalion, Reconnaissance Corps, on 6 June 1942 as 3rd Regiment, Reconnaissance Corps and finally on 1 January 1944 it was transferred to the Royal Armoured Corps as 3rd Reconnaissance Regiment. It remained part of the 3rd Infantry Division until August 1945. s at Sturminster Newton in Dorset, 28 August 1941. The 3rd Infantry Division remained in the United Kingdom, training for many years until it landed on Sword Beach on 6 June 1944D-Dayand fought through the Battle of Normandy, the Netherlands and later the invasion of Germany the, ending the war in Bremen. By the end of the war the 3rd Reconnaissance Regiment had lost 90 officers and other rankskilled in action.
Post-war
The regiment was placed in suspended animation in July 1946. The Territorial Army was disbanded at the end of the Second World War but this was a formality. TA units were reactivated on 1 January 1947, though no personnel were assigned until commanding officers and permanent staff had been appointed in March and April 1947. The 3rd Reconnaissance Regiment was reconstituted on 1 January 1947, converted to infantry with its former title and immediately disbanded.
