The 56th (London) Infantry Division was a Territorial Army infantry division of the British Army, which served under several different titles and designations. The division served in the trenches of the Western Front during the First World War. Demobilised after the war, the division was reformed in 1920 and saw active service again in the Second World War in Tunisia and Italy. The division was again disbanded in 1946 and reformed first as an armoured formation and then as an infantry division before final disbandment in 1961.

The Territorial Force (TF) was formed on 1 April 1908 following the enactment of the Territorial and Reserve Forces Act 1907 (7 Edw.7, c.9) which combined and re-organised the old Volunteer Force, the Honourable Artillery Company and the Yeomanry. On formation, the TF contained 14 infantry divisions and 14 mounted yeomanry brigades. One of the divisions was the 1st London Division. It was a wholly new formation, although its three infantry brigade headquarters (HQs) had previously existed in the Volunteers, as had most of its constituent units. The division comprised the first 12 battalions of the all-TF London Regiment, the first four London brigades of the Royal Field Artillery and the former Tower Hamlets Engineers; most of the supporting arms were newly raised. Essentially, all these units were based in inner London, while the 2nd London Division consisted of TF units recruited from suburban London. 1st London Division's HQ was at Friar's House in New Broad Street in the City of London.

On the outbreak of war in August 1914 the division's units had just left for their annual training camps, the 1st and 3rd London brigades around Wool, Dorset, and the 2nd at Eastbourne, Sussex. They immediately returned to their drill halls to mobilise, and then proceeded to their initial war stations guarding railways in Southern England. The TF was now invited to volunteer for Overseas Service, and most units did so; those men who had signed up for Home Service only, together with the floods of volunteers enlisting, were formed into reserve or 2nd Line units and formations with a '2/' prefix, while the parent unit took a '1/' prefix. 1/1st London Division immediately began supplying reinforcements to the Regular Army overseas. On 1 September the whole of 1/1st London Brigade, with its associated signal and medical units, set off to relieve the regular garrison of Malta; individual battalions joined the British Expeditionary Force (BEF) on the Western Front. By early January 1915 the 1st Line division had ceased to exist and its remaining units had been attached to its 2nd Line duplicate, the 2/1st London Division.

On 7 January 1916 the Army Council authorised the re-formation in France of the division as 56th (1/1st London) Division. As many as possible of the original units or other London units were assembled and by 21 February the bulk of the division had concentrated around Hallencourt between Abbeville and Arras under the command of Major General C. P. Amyatt Hull, an experienced officer who had until recently commanded an infantry brigade. Although the division was effectively a new formation, its constituent units were now experienced in trench warfare. After shaking down it took its place in the line in the Hébuterne sector.

The 56th Division's first operation as a complete formation was the attack on the Gommecourt Salient on 1 July 1916, the first day on the Somme. Extensive (and obvious) preparations were made for this attack, which was a diversion from the main Somme Offensive. The leading battalions gained a lodgement in the German front line with comparatively light losses, but they came under heavy counter-attack and were cut off from reinforcements and ammunition resupply by an intense barrage laid down in no man's land by the German artillery. At nightfall the survivors made their way back to British lines, the division having lost over 4,300 casualties, mainly among the seven attacking battalions.

The 56th (1/1st London) Division served on the Western Front for the rest of the war, taking part in the following operations:

1916

1917