Cavalry Reserve Regiments (United Kingdom)
Seventeen Cavalry Reserve Regiments were formed by the British Army on the outbreak of the Great War in August, 1914. These were affiliated with one or more active cavalry regiments, their purpose being to train replacement drafts for the active regiments. In 1915, the 3rd Line regiments of the Yeomanry were also affiliated with the Cavalry Reserve and, in September 1916, the Household Cavalry Reserve Regiment was formed in Windsor, supplying replacements to the dismounted Household Battalion. In 1917, the regiments underwent major reorganization, being reduced to ten in number.
Although nominally cavalry, many of the drafts ended up being converted into infantry in order to satisfy the manpower demands of trench warfare.
Despite being training and not combat formations, several were involved in the putting down of the Easter Rising in Dublin in April 1916. A little after noon on Easter Monday, a mixed troop of 9th and 12th Lancers, attached to the 6th Cavalry Reserve Regiment at Marlborough Barracks in Phoenix Park, was dispatched to investigate a "disturbance" at Dublin Castle. As they cantered down Sackville Street, they were fired upon by rebels who had taken up positions in and on the roof of the General Post Office. Three troopers were killed instantly and one was mortally wounded, becoming the first military casualties of the rising. The same evening, 1600 men of the 3rd Reserve Cavalry Brigade arrived from their barracks at the Curragh to support the local Dublin garrison.
Original August 1914 Formations
| Regiment | Location | Affiliated Regiments | Remarks |
| 1st Life Guards | Hyde Park | 1st Life Guards | |
| 2nd Life Guards | Windsor | 2nd Life Guards | |
| Royal Horse Guards | Regent's Park | Royal Horse Guards | |
| 1st | Aldershot | 1st Dragoon Guards 5th Dragoon Guards 3/1st Queen's Own Royal Glasgow Yeomanry 3/1st Sherwood Rangers Yeomanry | Absorbed into 4th, 1917 |
| 2nd | Aldershot | 2nd Dragoon Guards 6th Dragoons 3/1st Essex Yeomanry 3/1st Lothians and Border Horse | Absorbed into 4th, 1917 |
| 3rd | Canterbury | 3rd Dragoon Guards 6th Dragoon Guards 3/1st Northamptonshire Yeomanry 2/1st Surrey Yeomanry 1/1st Sussex Yeomanry | Absorbed into 6th, 1917 |
| 4th | Tidworth | 4th Dragoon Guards 7th Dragoon Guards 3/1st Warwickshire Yeomanry 3/1st Royal Gloucestershire Hussars 3/1st Queen's Own Worcestershire Hussars | Absorbed into 6th, 1917 |
| 5th | York | 1st Dragoons 2nd Dragoons 3/1st Northumberland Hussars 3/1st Queen's Own Yorkshire Dragoons 3/1st Yorkshire Hussars 3/1st East Riding Yeomanry | Absorbed into 6th, 1917 |
| 6th | Dublin | 5th Lancers 12th Lancers 3/1st City of London Yeomanry 3/1st County of London Yeomanry B Sqn composed mainly of a draft of 160 NCOs and men from 3/1st Welsh Horse Yeomanry | Absorbed into 1st, 1917 |
| 7th | Tidworth | 9th Lancers 21st Lancers 3/1st Royal Buckinghamshire Yeomanry 3/1st Berkshire Yeomanry | Absorbed into 1st, 1917 |
| 8th | The Curragh | 16th Lancers 17th Lancers 3/1st Queen's Own Dorset Yeomanry 3/1st Queen's Own Oxfordshire Hussars | Absorbed into 1st, 1917 |
| 9th | Shorncliffe | 3rd Hussars 7th Hussars 3/2nd County of London Yeomanry 3/3rd County of London Yeomanry | Absorbed into 2nd, 1917 |
| 10th | The Curragh | 4th Hussars 8th Hussars 3/1st Duke of Lancaster's Own Yeomanry 2/1st Lancashire Hussars 3/1st Westmorland and Cumberland Yeomanry | Absorbed into 2nd, 1917 |
| 11th | Tidworth | 10th Hussars 18th Hussars 3/1st Hampshire Yeomanry 3/1st North Somerset Yeomanry 3/1st Royal Wiltshire Yeomanry | Absorbed into 5th, 1917 |
| 12th | Aldershot | 11th Hussars 13th Hussars 3/1st Leicestershire Yeomanry 3/1st Lincolnshire Yeomanry 3/1st Staffordshire Yeomanry | Absorbed into 3rd, 1917 |
| 13th | Colchester | 14th Hussars 20th Hussars 3/1st Bedfordshire Yeomanry 3/1st Hertfordshire Yeomanry | Absorbed into 5th, 1917 |
| 14th | Longmoor | 15th Hussars 19th Hussars 3/1st Derbyshire Yeomanry 3/1st South Nottinghamshire Hussars | Absorbed into 3rd, 1917 |
Formed in 1916
After 1917 re-organization
| Regiment | Location | Affiliated Regiments | Remarks |
| 1st Life Guards | Hyde Park | 1st Life Guards | |
| 2nd Life Guards | Windsor | 2nd Life Guards | |
| Royal Horse Guards | Regent's Park | Royal Horse Guards | |
| Household Cavalry | Windsor | Household Battalion | Disbanded early 1918 |
| 1st | The Curragh | 5th Lancers 9th Lancers 12th Lancers 16th Lancers 17th Lancers 21st Lancers 3/1st Bedfordshire Yeomanry 3/1st Lincolnshire Yeomanry 3/1st City of London Yeomanry 2/1st Surrey Yeomanry 3/1st East Riding Yeomanry | |
| 2nd | The Curragh | 3rd Hussars 4th Hussars 7th Hussars 8th Hussars 3/1st Queen's Own Dorset Yeomanry 2/1st Lancashire Hussars 3/1st County of London Yeomanry 3/3rd County of London Yeomanry 3/1st South Nottinghamshire Hussars 3/1st Queen's Own Oxfordshire Hussars 3/1st Westmorland and Cumberland Yeomanry | |
| 3rd | Aldershot | 11th Hussars 13th Hussars 15th Hussars 19th Hussars 3/1st Royal Buckinghamshire Yeomanry 3/1st Leicestershire Yeomanry 3/1st Staffordshire Yeomanry 3/1st Royal Wiltshire Yeomanry 3/1st Sherwood Rangers Yeomanry | |
| 4th | Aldershot | 1st Dragoon Guards 2nd Dragoon Guards 5th Dragoon Guards 6th Dragoons 3/1st Derbyshire Yeomanry 3/1st Essex Yeomanry 3/1st Queen's Own Royal Glasgow Yeomanry 3/1st Hampshire Yeomanry 3/2nd County of London Yeomanry 3/1st Lothians and Border Horse | |
| 5th | Tidworth | 10th Hussars 14th Hussars 18th Hussars 20th Hussars 3/1st Northumberland Hussars 3/1st Yorkshire Hussars 3/1st Warwickshire Yeomanry 3/1st Royal Gloucestershire Hussars 3/1st Queen's Own Worcestershire Hussars | |
| 6th | Tidworth | 3rd Dragoon Guards 4th Dragoon Guards 6th Dragoon Guards 7th Dragoon Guards 1st Dragoons 2nd Dragoons 3/1st Berkshire Yeomanry 3/1st Hertfordshire Yeomanry 3/1st Duke of Lancaster's Own Yeomanry 3/1st Northamptonshire Yeomanry 3/1st North Somerset Yeomanry 3/1st Queen's Own Yorkshire Dragoons |