The Durham Group of National Defence Companies was formed early in 1939. These companies, based at Gateshead, Sunderland, Durham, Bishop Auckland and Stockton-on-Tees, were set up to guard certain Vulnerable Points.  In charge were Lieutenant-Colonel J.E. Stafford and Major R. Boyes-Stone, and their total strength was 18 officers and 500 men, mostly first world war veterans, with an average age of 45 to 50 years. They were mobilised on August 22nd 1939, when the code word ALLENBY was issued, and were immediately renamed 41 Group, National Defence Companies with headquarters at the offices of Messrs. Liddell and Stafford in the Royal Exchange Buildings, Hood Street, Newcastle (above Mawson, Swan and Morgan).

They were immediately enlisted, armed and provided with uniforms, and on August 24th they were ordered to occupy the 17 airfields, docks, ammunition depots and other Vulnerable Points assigned to them. They suffered their first casualty before war was declared; Private G.R. Milburn was killed on August 29th by a train on Croxdale Viaduct. In December 1939, 41 Group, National Defence Companies was renamed the 13th (Home Defence) Battalion, Durham Light Infantry.

In September 1940 the 13th Battalion gave birth to another, the 2nd/13th, and was itself renamed the 1st/13th (Home Defence) Battalion, Durham Light Infantry. However the 2nd/13th was renamed the 18th Battalion in December 1940 and the 1st/13th then reverted to the 13th Battalion once again. The 18th Battalion continued to carry out the original role of the 13th -guarding airfields and other Vulnerable Points- but the men of the 13th became anti-raid troops mostly at the radio stations of the Bomber Command airfields in Yorkshire. During 1941 the battalion was gradually converted into field force unit, as physically fit younger men took the place of the older ones. In November 1941 the 13th Battalion became the 30th Battalion D.L.I. and this battalion also absorbed the 18th D.L.I. which latterly had been guarding Vulnerable Points in Lincolnshire. Early in 1942, in preparation for taking on an anti-invasion mobile counter-attack role, all remaining older and low category men were posted to the 30th Battalion Royal Northumberland Fusiliers in exchange for all their fully fit men. Training proceeded over the summer of 1942 and then, in typical army fashion, on November 20th 1942 the 30th Battalion, Durham Light Infantry was disbanded.