Aldershot Command was the home of the 1 Infantry Division and 2 Infantry Division. Together they formed the ‘Spearhead Corps’ for deployment overseas at times of crisis, although there was no separate corps headquarters. On the outbreak of war, Aldershot Command formed the Headquarters, I Corps, which was mobilised and deployed to France with the British Expeditionary Force. Lieutenant General DILL travelled across to France on H.M.S. Skate on 14 September 1939. Advanced elements of the corps headquarters arrived on 22 September and concentrated around Laval.

The 1 Infantry Division arrived in France on 20 September 1939, with the 2 Infantry Division arriving a day later. The first Territorial Army formation that was mobilized and sent to France was the 48 (South Midland) Infantry Division. It arrived on 5 January 1940 and came under command of I Corps. The German forces attacked the Netherlands, Belgium and France on 9 May 1940, so I Corps moved up into Belgium. It was involved in the battle for St. Omer and La Bassee between 23 and 29 May 1940. The rapid advance of the German forces led to the Corps retreating into the Dunkirk salient, from where it was evacuated on or about 1 June 1940.