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: 
1st Battalion, with 15th Infantry Brigade of the 5th Infantry Division, seeing action in Sicily and Italy.

2nd Battalion, initially stationed in India, it fought in Burma as part of the 26th Indian Infantry Division and the 82nd (West Africa) Division.

4th and 5th Territorial Army Battalions, both serving with the 150th Infantry Brigade of the 50th (Northumbrian) Infantry Division, saw service in France and North Africa where they were captured during the Battle of Gazala.

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, originally with the 23rd (Northumbrian) Division but later the 50th Division, saw service in France, North Africa, Sicily and North West Europe.

8th Battalion was formed for home defence.

9th Battalion was formed for garrison duty (and later converted into the 108th Light Anti-Aircraft Regiment, Royal Artillery, serving with the 52nd (Lowland) Infantry Division from March 1942)
10th Battalion 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 Division.

The 11th, 12th and 13th Battalions were all formed in 1940.

In 1942, the 12th Battalion was converted to armour as the 161st Regiment 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.
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 the 43rd (Wessex) Reconnaissance Regiment, which had suffered heavy losses when its transport was sunk on the way to France to fight in the Battle of Normandy.
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: 
1st Battalion, with 15th Infantry Brigade of the 5th Infantry Division, seeing action in Sicily and Italy.
2nd Battalion, initially stationed in India, it fought in Burma as part of the 26th Indian Infantry Division and the 82nd (West Africa) Division.
4th and 5th Territorial Army Battalions, both serving with the 150th Infantry Brigade of the 50th (Northumbrian) Infantry Division, saw service in France and North Africa where they were captured during the Battle of Gazala.
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, originally with the 23rd (Northumbrian) Division but later the 50th Division, saw service in France, North Africa, Sicily and North West Europe.
8th Battalion was formed for home defence.
9th Battalion was formed for garrison duty (and later converted into the 108th Light Anti-Aircraft Regiment, Royal Artillery, serving with the 52nd (Lowland) Infantry Division from March 1942)
10th Battalion 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 Division.
The 11th, 12th and 13th Battalions were all formed in 1940.
In 1942, the 12th Battalion was converted to armour as the 161st Regiment 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. 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 the 43rd (Wessex) Reconnaissance Regiment, which had suffered heavy losses when its transport was sunk on the way to France to fight in the Battle of Normandy.
Green Howards