WW2 Green Howards officers mess dress with pants and waistcoat (Officers uitgaans tenue WW2 Green Howards)

During the Second World War, the regiment was again increased in size, although not to as large an extent as in the 1914–1918 conflict. In all, twelve battalions saw service: the 1st, with 15th Brigade, and 2nd regular army Battalions, the 4th and 5th Territorial Army Battalions, both serving with 150th Brigade, the 6th and 7th Battalions (both formed as 2nd Line duplicates of the 4th and 5th, when the Territorial Army was doubled in size in 1939, served with 69th Brigade), the 8th was formed for home defence, the 9th was formed for garrison duty (and later converted into the 108 LAA Regt RA), the 10th was formed by the conversion of the 2nd East Riding Yeomanry (a war-time duplicate of this yeomanry unit) in 1940 and subsequently becoming the 12th (Yorkshire) Parachute Battalion attached to the 5th Parachute Brigade and part of the 6th Airborne DivisionThe 11th, 12th and 13th were all formed in 1940.

In 1942, the 12th Battalion was converted to armour as the 161st Regiment in the Royal Armoured Corps, but retained its Green Howards cap badge on the black beret of the Royal Armoured Corps as did all other infantry units converted in the same way.^[13] In October 1943 it was then converted again, this time to the reconnaissance role, as 161st (Green Howards) Regiment in the Reconnaissance Corps. It never went into action as a regiment, but provided a replacement squadron to 43rd Reconnaissance Regiment, which had suffered heavy losses when its transport was sunk on the way to France to fight in the Battle of Normandy.