The 2nd Battalion was a Regular Army unit that was based in Northern Ireland at the outbreak of war. The battalion, under the command of Lieutenant Colonel Manley Angell James, were joined with the 4th and 5th Battalions of the regiment in the 133rd (Royal Sussex) Infantry Brigade as part of the 44th (Home Counties) Infantry Division. The 4th Royal Sussex Regiment was then commanded by Lieutenant Colonel Lashmer Whistler. The 2nd Battalion was sent to France in April 1940, to join the British Expeditionary Force (BEF), taking part in the Battle of France and the subsequent retreat to Dunkirk where they were evacuated to England in the Dunkirk evacuation. The brigade was sent to North Africa in May 1942, where they fought in the Battle of Alam el Halfa in September 1942 and the Battle of El Alamein in October 1942.