Mk I was introduced from March 1916. It is identified by its short barrel and recuperator above the barrel.
Mark III
The longer-barrelled Mk III soon followed, with a heavier breech to balance the gun. It retained the recuperator above the barrel.
Mark V
Mk V, dating from July 1917, moved the recoil buffer and recuperator into a single housing below the barrel, which was common for all new British artillery developed during World War I. It also had a lighter breech with the gun balanced by the redesigned recoil system and altered gun positioning on the cradle.[2] Mk V also relocated the loading platform from the railway wagon to the revolving gun mounting, which now allowed 120° of traverse, and by overhanging the opposite side provided crew access when the gun fired to the side (90° traverse) and also helped to balance it.[2]
^Mk I = Mark 1, Mk III = Mark 3, Mk V = Mark 5. Britain used Roman numerals to denote Marks (i.e. models) of ordnance until after World War II. Hence this article covers the first, third and fifth models of British 12-inch howitzers. Mks II and IV were the unrelated BL 12-inch siege howitzer.