The title of Light Infantry was given in honour of its former commander General Sir John Moore in 1809, and in 1821 the regiment was given royal status when King's Own was added to its title, becoming the 51st (2nd Yorkshire, West Riding, The King's Own Light Infantry) Regiment.

[3] The Childers Reforms also combined Militia and rifle volunteer units into the regiments formed in 1881.

[8] Following the outbreak of the Second Boer War in October 1899, the battalion transferred to South Africa, where it fought at the Battle of Modder River in November 1899.

In October that year 790 officers and men of the battalion left Point Natal on the SS Staffordshire bound for Malta, where they were then stationed.

On 15 March 1912, a ceremony was held for the departure from the Colony of the Governor, Sir Frederick Lugard and it was reported that a guard of honour and a military band was provided by men of the King's Own Yorkshire Light Infantry.

[14] The 2/4th and 2/5th Battalions landed at Le Havre as part of the 187th Brigade in the 62nd (2nd West Riding) Division in January 1917 also for service on the Western Front.

[14] Lt-Col Oliver Watson commanding 5th KOYLI was awarded the Victoria Cross (VC) posthumously for his actions at Rossignol Wood on 27 March 1918,[16] and Sergeant Laurence Calvert of the same battalion was awarded the VC for actions at the Battle of Havrincourt (2 September 1918).

[17] Corporal Ernest Hayes, who was awarded three Military Medals in 1918 for acts of bravery on the Western Front, served with the 2/4th Battalion.

[14] Stuart Cloete, a South African novelist, served with the 9th Battalion at the Battle of the Somme in autumn 1916.

In April 1940, with the brigade, the battalion was sent to Aandelsnes, Norway where they saw service as part of "Sickleforce" in the Norwegian Campaign and earned its first battle honour "Kvam" before it was evacuated on 1 May / 2 May.

[22] The 5th Battalion was transferred to the Royal Artillery before the war and converted into the 53rd (KOYLI) Light Anti-Aircraft Regiment.

It served in the Battle of France and on the beach at the Dunkirk Evacuation and was then sent to Egypt, joining the British Eighth Army.

It served with the 10th Armoured Division at the Second Battle of El Alamein and then in AA defence of airfields during the Eighth Army's dash to Tunisia.

Afterwards, it landed in Sicily and in Italy, where it served as infantry and mortar troops as well as LAA gunners.

This saw action in the Anglo-Iraqi War and Syria–Lebanon Campaign, then joined 4th Indian Division, with which it served in Operation Crusader, at Alamein, in Tunisia and Italy.

The new formation continued to wear their King's Own Yorkshire Light Infantry cap badge on the black beret of the RAC.

[30] Reduced to one regular battalion after the war, the regiment was deployed to Malaya in 1948 to take part in peacekeeping and counter-insurgency operations during the Malayan Emergency.