Background
The cavalry had existed as a horse-mounted force within the British Army since it became recognisable as such in the period between the creation of Cromwell’s New Model Army during the civil wars of the 17th Century and the Act of Union with Scotland in the early 18th Century. By 1914, with the recent learning from the Second Boer War, its primary role had become one of battlefield reconnaissance and mobile exploitation of offence. The major campaign of the Great War for British use of cavalry was that of Egypt and Palestine, for it found opportunities in other theatres more limited, particularly in the entrenched phase of war in France and Flanders and in the mountainous battlefield of Salonika. At times, the cavalrymen fought dismounted in trench warfare.
Cavalry units and formations
The unit of the cavalry was called a regiment (which can be confusing as this differs from the infantry and artillery). Each unit was of a category known as either the Household Cavalry, Dragoon Guards, Dragoons, Hussars, or Lancers. These were historic, rather archaic, terms and by 1914 in war fighting terms there was essentially no difference in organisation, armament, or role between the different types.
The British regiments of cavalry belonged individually to the Regular Army, the Special Reserve, or the Yeomanry. The latter was the cavalry of the Territorial Force. Britain also called upon cavalry regiments of the Indian Army, Canadian Expeditionary Force, and the Australian Light Horse and New Zealand Mounted Rifles. This section of the Long, Long Trail deals only with the Regular and Special Reserve elements.
The regiments of cavalry were in some cases formed into formations known as Cavalry Brigades, which in turn came under Cavalry Divisions. Later, units known as Corps Cavalry Regiments were formed, under orders of the headquarters of Corps.
Mounted units were also later formed for the Machine Gun Corps, known as Machine Gun Corps (Cavalry).
The Regular Army regiments of cavalry included three that were often collectively known as the Household Cavalry (1st and 2nd Life Guards and Royal Horse Guards); seven regiments of Dragoon Guards; three of Dragoons; twelve of Hussars; and six regiments of Lancers. In the mists of time, these various types of cavalry had ha different roles and armamenets, but by the Great War the differences were essentially in name only.
There were three regiments of the Special Reserve: the King Edwards Horse, the North Irish Horse and the South Irish Horse.
The histories of each regiment and formation can be found on the Long, Long Trail.
A cavalryman’s progress
Pre-war: although variation can be seen in men’s service records, largely depending on when he was enlisted and the regiment to which he was allocated, most recruits would begin training at one of the Cavalry Depots. This was a unit responsible for recruit training and the keeping of mobilisation stores, and was associated with certain regiments of the cavalry. Once the man had been trained, essentially to ride, he was available to be sent to his regiment.
War time: with most cavalry regiments already overseas and quickly sent overseas, their abaility to continue the training of recruits was curtailed. A number of Reserve regiments of Cavalry were formed for this purpose, wach of which was associated with certain regiments of the cavalry. A rectuit might therefore begin at a Cavalry Depot, then go to a Reserve Regiment, then be posted to an active regiment in a theatre of war.
Reading
The multi-volume history of the British cavalry by the Marquess of Anglesey is a standard source. The Great War volumes can all be read at Archive.org.
Most of the regiments have a published history. See details at the relevant regimental page on this site.