Short Answer: Because it was created in a time period when the English Monarchy and the English Parliament were fighting (sometimes literally) over power, and Parliament were able to establish control over the Army.

Long Answer: Prior to the English Civil War, England didn't really have a standing army. When an army was needed, forces were raised from mercenaries, local militias, and private forces of the nobility. This meant that there wasn't ever a Royal Army per se. The Navy, meanwhile, couldn't simply be cobbled together by relying on conscription and mercenaries, and so truly was a 'standing' force, loyal to the Crown.

During the English Civil War, Parliament realized that the regional forces they could raise were not going to be enough to win the war against the king, and legislated for a truly professional army (complete with careerist officers and sergeants)- this was the New Model Army. This army was the basis of the current British Army, and was not termed the Royal Army for the fairly obvious reason that it was created to fight the King.

This army won the Civil War, and remained throughout the Interregnum; upon the Restoration of the English monarchy, it was disbanded. Charles II, however, supported the creation of an English Army, and raised one, which necessarily included elements of the New Model Army. During this period, Scotland and Ireland actually technically had their own standing armies as well; it wasn't till the Act of Union in 1707 that the English Army became the British Army.

So why wasn't it called the Royal Army? Because at this time, there was still significant conflict between Parliament and the Crown as to who possessed the real power in the land. Parliament feared that allowing the King to keep a large standing army would give him the power to ignore Parliament completely; the expense of a large standing army was also not remembered with fondness.

In 1688, Parliament invited William of Orange (who would become William III) to invade England and take James II's crown, which he did in the Glorious Revolution. One of the many effects of this was that some of the regiments refused to follow the new King, since they didn't recognize his validity. Since these forces were stationed in England, they were under the jurisdiction of common law courts; however, those courts didn't have the ability to punish crimes like mutiny. This wasn't a situation that had ever occurred before, since previously any mutinies would have taken place in wartime (since this was the only time that an army would have existed) and would have been punished under martial law.

It was Parliament that resolved this issue, setting the basis for military law with the first Mutiny Act, and establishing their own control over the Army.

By the time of the Royal Air Force, meanwhile, the debate between Crown and Parliament was so far buried that it would never come up, and Parliament would have had no issue with naming it the Royal Air Force- since the 'Royal' control would be in name only.

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!

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