The Royal Regiment of Artillery, commonly referred to as the Royal Artillery (RA), is the artillery

Artillery

Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

 arm of the British Army

British Army

The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...

. Despite its name, it comprises a number of regiments.
The introduction of artillery into the British Army came as early as the fourteenth century but was not a permanent body, Henry VIII recognised what artillery could achieve and created a semi-permanent body of artillery.