The 3rd Division, known as 'The Iron Division' or 'Monty's Ironsides', was formed on the orders of Wellington in June 1809 as he reorganised his brigades into larger formations in Portugal to continue the Peninsular War against Napoleon.
Early in 1940, Montgomery, then a major-general commanding 3rd Division, introduced the famous three-in-one red and black triangle design as the divisional badge. It represents the division's basic make-up of three infantry brigades, each consisting of three battalions.
For the invasion of Normandy, the division contained perhaps the most comprehensive cross-section of soldiers from all parts of the United Kingdom. Its make-up was as follows:

8 Infantry Brigade: Ist Battalion, The Suffolk Regiment; 2nd Battalion, The East Yorkshire Regiment; 1st Battalion, The South Lancashire Regiment.

185 Infantry Brigade: 2nd Battalion, The Royal Warwickshire Regiment; 1st Battalion, The Royal Norfolk Regiment; 2nd Battalion, The King's Shropshire Light Infantry.

9 Infantry Brigade: 2nd Battalion, The Lincolnshire Regiment; 1st Battalion, The King's Own Scottish Borderers; 2nd Battalion, The Royal Ulster Rifles.

27th Armoured Brigade: 13/18 Royal Hussars; 1st East Riding Yeomanry; The Staffordshire Yeomanry.

Divisional Troops: 3rd Reconnaissance Regiment RAC; 3rd Divisional Engineers; 3rd Divisional Signals; 7th Field Regiment, Royal Artillery; 33rd Field Regiment, Royal Artillery; 76th Field Regiment, Royal Artillery; 20th Anti-Tank Regiment, Royal Artillery; 92nd (Loyals) Light Anti-Aircraft Regiment, Royal Artillery; 2nd Battalion, The Middlesex Regiment (Machine Gun).