Digitised by Google Books from the collection at the New York Public Library https://books.google.com/books?id=fESe-2NxcGMC Page 11 says  "The  earlier campaigns of the war had demonstrated the necessity of a greater strength of heavy artillery, and it was therefore decided 
to increase the strength of the Royal Garrison Artillery by a very considerable addition to the number of its units. 211 6-inch Howitzer Siege Battery was one of the additional units formed under this decision." The Battery arrived in France 1 December 1916. Initially it was part of the 40th H. A Group (page 14) but later was transferred to the 68th H. A. Group (page 30).Heavy Artillery Groups became known as RGA Brigades from 17 December 1917, but it appears that the two terms were used almost interchangeably, (according to the website The Long, Long Trail) The Battery remained on the Western Front throughout the war.  From the end of March 1919 it became part of the Rhine Army of Occupation, until disbanded in July 1919.