Dragoon Guards is a designation that has been used to refer to certain heavy cavalry regiments in the British Army since the 18th century. While the Prussian and Russian armies of the same period included dragoon regiments among their respective Imperial Guards, different titles were applied to these units.
The British Army first used the designation in 1746, when the King's Own Regiment of Horse, the Queen's Own Royal Regiment of Horse (prior to 1727 the Princess of Wales's Own) and the 4th Horse were redesignated as the 1st, 2nd and 3rd Dragoon Guards respectively. In 1788 the four remaining regiments of Horse were converted into the 4th to 7th Dragoon Guards. At the beginning of the French Revolutionary War the British Army maintained seven regiments of Dragoon Guards, plus six of Dragoons and fourteen of Light Dragoons. During the 19th and esrly 20th centuries the seven regiments of Dragoon Guards were classed as medium cavalry while the three remaining Dragoon regiments were heavy cavalry.
The exercise of converting from "Horse" (heavy cavalry) to "Dragoon" (formerly mounted infantry) was intended to save money--Dragoons were paid less than Horse and rode an inferior breed of horses. The change was accordingly very unpopular among the regiments affected. To compensate for the fall in salary and status, the impressive sounding title of "Dragoon Guards" was adopted. The Dragoon Guards remained as cavalry of the line and did not become Household troops in any sense.
The Regiments of Horse that were converted to Dragoon Guards took precedence over all other cavalry regiments of the Line, which were at the time exclusively dragoons. As the senior regiments, they could not take numbers sequential with those of the existing dragoon regiments, so they needed a new title and numbering system. Hence they were termed Dragoon Guards, the guards appellation giving them higher prestige, and allowing them to be numbered in their own sequence.