The 3rd (United Kingdom) Division, known at various times as the Iron Division, 3rd (Iron) Division, Monty's Iron Sides or as Iron Sides; is a regular army division of the British Army. It was created in 1809 by Arthur Wellesley, 1st Duke of Wellington, as part of the Anglo-Portuguese Army, for service in the Peninsular War, and was known as the Fighting 3rd under Sir Thomas Picton during the Napoleonic Wars. The division is also sometimes referred to as the Iron Division, a nickname earned during the bitter fighting of 1916, during the First World War. The division's other battle honours include: the Battle of Waterloo, the Crimean War, the Second Boer War, the Battle of France (1940) and D-Day landings of 6 June 1944. It was commanded for a time, during the Second World War, by Bernard Montgomery. The division was to have been part of a proposed Commonwealth Corps, formed for a planned invasion of Japan in 1945–46, and later served in the British Mandate of Palestine.
During the Second World War, the insignia became the "pattern of three" — a black triangle trisected by an inverted red triangle, created by Bernard Montgomery to instil pride in his troops.
The division was part of the Allied British and Portuguese forces that took part in the Peninsular War and fought in the Battle of Sabugal, Battle of Orthez, Siege of Badajoz (1812), Battle of Salamanca, Battle of Nivelle, Battle of Fuentes de Oñoro, Battle of Vitoria, Battle of Bussaco and the Battle of the Pyrenees