The gun with its increased length of 50 calibres was an attempt to extract a higher velocity, and hence more range and armour-piercing capability, from the 9.2-inch gun. Like other British 50-calibre guns of the period, it was relatively unsuccessful and was the last model of 9.2-inch gun Britain built.
After the scrapping of these ships, these guns and mountings were retained in storage. There was the intention, at one point, early during World War Two, to use them as armament for small monitors which would have been reduced versions of the Roberts-class monitors; this however never advanced beyond the planning stage.
^Mark XI = Mark 11. Britain use Roman numerals to denote Marks (models) of ordnance until after World War II. Hence this was the eleventh model of BL 9.2-inch gun.
References
^1908–1920 : Dates of commissioning and scrapping of the ships. The guns were not used again after removal.
^The National Archives of the United Kingdom, Kew. SUPP 6/61