Same as 5th Regt RA they used to be 5 RHA back in the 1980s. I assume their titles were changed in a re roleing exercise back then, 4th Regt as a normal field Regiment and 5th as a Heavy. As confirmation i show you the 5th Regiment "Cypher".
Just to clarify. I understand that 4th Regt used to be RHA a long time ago. What I am saying is that on the official Army Website, they are down as 4th Regt RHA. There are only three RHA Regts â 1st, 3rd and 7th.