Originally raised as part-time cavalry for home defence and internal security, the regiment sent mounted infantry to serve in the Second Boer War.

After Britain was drawn into the French Revolutionary Wars, Prime Minister William Pitt the Younger proposed in 1794 that the counties should form a force of Volunteer Yeoman Cavalry (Yeomanry) that could be called on by the King to defend the country against invasion or by the Lord Lieutenant to subdue any civil disorder within the county.

The County of Lancaster (Lancashire) raised the following independent Troops:[5] Most volunteer cavalry was disbanded after the Treaty of Amiens in 1802, but the peace was shortlived, and many troops were reformed or newly formed:[5] The Yeomanry declined in importance and strength after the Battle of Waterloo, but in the absence of police it remained available for use in aid of the civil power, particularly in the industrial North of England.

[5] It participated in the so-called Peterloo Massacre in 1819, when 11 unarmed civilians were killed and around 400 injured by the action of the Regular and Yeomanry cavalry who had been called out to control a demonstration at St Peter's Fields, Manchester.

The LHVs were less expensively dressed and less socially exclusive than the Yeomanry, but they occupied an anomalous position between them and the Rifle Volunteers, and most were shortlived.

This was never more than a paper organisation, but from April 1893 the Army List showed the Yeomanry regiments grouped into brigades for collective training.

[14] Following a string of defeats during Black Week in early December 1899, the British government realised that it would need more troops than just the Regulars to fight the Second Boer War.

[5][6][8][14][19][20][21][22][23][24] 2nd Battalion, IY, including 32nd (Lancashire) Company, landed in South Africa on 28 February 1900 and was sent to Naauwpoort as part of a Yeomanry brigade under Major-General John Brabazon.

[23][25] 8th Battalion, IY, including 23rd (Lancashire) Company, landed in South Africa on 5 March 1900 [21][23] From early May 1900 23rd (Lancashire) and 24th (Westmorland & Cumberland) Companies of the 8th Bn and 19th (Paget's Horse) Bn were serving under the Earl of Erroll with Sir Charles Warren's Column operating in Griqualand West.

Warren had placed insufficient pickets and before dawn on 30 May a force of Boers surrounded the camp, infiltrated into the garden and prepared to attack.

The two IY companies advanced to support their picket on the southern ridge and brought their two Colt machine guns into action.

Leaving a party to keep down enfilading fire from the garden, and the Paget's Horse detachment to protect the machine guns, the rest of the IY advanced by rushes over open ground towards the ridge.

[8][35] It was now distributed as follows:[5][36][37] The Duke of Lancaster's, together with the Lancashire Hussars and the Westmorland & Cumberland Yeomanry, was attached to the TF's Welsh Border Mounted Brigade for peacetime training, but would be assigned to other formations in the event of war.

[38][36][39][40][41] Under the 1907 Act, the TF was intended to be a home defence force for service during wartime and members could not be compelled to serve outside the country.

[8][36][44][45] 12th (Service) Bn was originally raised as a Kitchener battalion on 7 October 1914 at Ashton-under-Lyne and had already seen considerable action with 52nd Brigade of 17th (Northern) Division, in the Ypres Salient in 1915–16, on the Somme in 1916, including the Battle of Delville Wood, and in the Arras Offensive earlier in 1917.

However, breakthroughs to the north and south rendered the position at Flesquières untenable, and 17th (N) Division was involved in a fighting retreat back to the River Ancre, where a defence line was established.

[44][47][48] During the Allied Hundred Days Offensive 17th (N) Division came into action during the Second Battle of the Somme, capturing Martinpuich on 25 August after 12th (DLOY) Bn encircled it from the south.

Another attempt by the battalion at an outflanking move, against Le Transloy on 1 September, was stopped by machine gun fire, but the village was heavily shelled overnight and 12th (DLOY) Bn, attacking at dawn, worked round the flank once more, forcing the Germans to evacuate..[44][49] The advance continued, with Third Army closing up to the Germans' Hindenburg Line defences.

After being reinforced with a mixture of old soldiers and raw recruits, 12th (DLOY) Bn advanced again on 31 October, fording the river and pushing onto the ridge beyond against German shelling and rearguards.

By July 1915, it was under the command of the 2/1st Western Mounted Brigade (along with the 2/1st Westmorland and Cumberland Yeomanry[40] and the 2/1st Lancashire Hussars[39]) and in March 1916 was at Cupar, Fife.

It did not receive a regimental number until 15 April when (as most other TA units had already done) it split into two:[8][56][57] By the end of 1940 77th Medium Rgt was attached to 53rd (Welsh) Division in Northern Ireland and remained there for over two years.

[64][65][66][67][68][69] VIII Corps was then 'grounded' to provide transport and fuel to Second Army's pursuit force and only played a minor role in Operation Market Garden (the Battle of Arnhem).

[73][74][75] After the Rhine crossing 21st Army Group began a rapid advance across northern Germany and there was little call for medium artillery.

[59][78] IV Corps HQ was sent to Middle East Forces (MEF) at the beginning of 1942 and the regiment and 47th Division reverted to the direct control of Southern Command.

[60] During December 1942 78th (DLOY) Medium Rgt came under War Office control preparatory to going overseas,[80] and it had left for MEF by February 1943.

[61] It served in Palestine and Syria then by January moved to join in the Italian Campaign as part of 6th Army Group Royal Artillery (6 AGRA).

On 1 April 1983, it rejoined the Royal Armoured Corps as a home defence reconnaissance unit, being equipped with Land Rovers.

[90] The 19th century dragoon helmets with white plumes were still worn for special occasions but only officers were required to obtain the pre-1903 full dress tunics and gold laced belts for attendance at court levees, as late as 1938.

[14] In the white metal cap badge the rose appeared within a laurel wreath, surrounded by a Garter strap bearing the title 'DUKE OF LANCASTER'S OWN', surmounted by a royal ducal coronet.

In the version worn during World War II the Garter strap was left off, and the regimental title appeared on a scroll intertwined through the wreath.