The 1st Battalion, London Irish Rifles formed part of the 1st London Infantry Brigade, itself part of the 1st London Division. In November 1940 the battalion transferred to the 2nd London Brigade, which was soon renumbered as the 168th (London) Infantry Brigade, due to the division's redesignation as the 56th (London) Infantry Division. From the outbreak of the Second World War in September 1939 until late July 1942, the battalion was in training, mainly in southeast England. The battalion left England in August 1942 to serve in the Middle East. In April 1943 the battalion, together with the rest of the 168th Brigade, was temporarily transferred to the 50th (Northumbrian) Infantry Division and fought in the Allied invasion of Sicily, codenamed Operation Husky, in July/August. The battalion, as part of the 168th Brigade, returned to the 56th Division in Italy in October, and took part in major actions during the Italian Campaign at Fosso Bottacetto south of Catania, Monte Camino, Monte Damiano, the Garagliano crossing during the first Battle of Monte Cassino and Aprilia (Anzio), and at the Gothic Line, and, transferring back to the 167th Brigade, the battalion played a leading role in the final Allied offensive in Northern Italy during April 1945. In the month that they spent fighting in the Anzio beachhead, the 1st Battalion's casualties totalled 600 officers and other ranks killed, wounded and missing. Some 700 men of the London Irish Rifles were killed in action during the Second World War.