BL 6 - inch Mk VII naval gun The BL 6 inch Gun Mark VII ( and the related Mk VIII ) was a British naval gun dating from 1899 , which was mounted on a heavy traveling carriage in 1915 for British Army service to become one of the main heavy field guns in the First World War , and also served as one of the main coast defence guns throughout the British Empire until the 1950s . Background . The gun superseded the QF 6 - inch gun of the 1890s , a period during which the Royal Navy had evaluated QF technology ( i . e . loading propellant charges in brass cartridge cases ) for all classes of guns up to 6 inch to increase rates of fire . BL Mk VII returned to loading charges in silk bags after it was determined that with new single - action breech mechanisms a 6 - inch BL gun could be loaded , vent tube inserted and fired as quickly as a QF 6 inch gun . Cordite charges in silk bags stored for a BL gun were also considered to represent a considerable saving in weight and magazine space compared to the bulky brass QF cartridge cases . Naval gun . The gun was introduced on the s of 1898 ( commissioned September 1901 ) and went on to equip many capital ship s , cruiser s , monitor s , and smaller ships such as the which served throughout World War II . Mk VIII in Naval service was identical to Mk VII , except that the breech opened to the left instead of to the right , for use as the left gun in twin turrets . Guns were mounted in the following ships : < br style = " clear : left ; " > In World War II the gun was used to arm British troop ships and Armed Merchant Cruisers , including , which briefly fought the German 11 - inch gun battlecruisers and in November 1939 , and which similarly sacrificed herself to save her convoy from the 11 - inch cruiser in November 1940 . World War I field gun . They were first sent to France in 1915 mounted on improvised rectangular - frame field carriages designed by Admiral Percy Scott , based on the design he had improvised for 4 . 7 - inch guns in the Second Boer War , and were successful . However , elevation and hence range was limited with the Scott carriages so a proper carriage , MK II , was introduced early in 1916 , allowing elevation to 22° . Carriages Mks III , V and VI also appeared . It was operated by the Royal Garrison Artillery , as were all the larger guns , in World War I , in batteries of 4 guns . Following its successful employment in the Battle of the Somme its role was defined as counter - battery fire and also they " were most effective for neutralising defences and for wire cutting with fuze 106 [ a new fuze which reliably burst instantly above ground on even slight contact , instead of forming craters ] " , also for long - range fire against " targets in depth " . It was superseded by the lighter and longer - range BL 6 - inch Gun Mk XIX which was introduced from October 1916 but the Mk VII remained in service to the end of World War I . < br style = " clear : left ; " > Coast defence gun . The 6 - inch Mk VII gun , together with the 9 . 2 - inch Mk X gun , provided the main coast defence throughout the British Empire , from the early 1900s until the abolition of coast artillery in the 1950s . Many guns were specially built for army coast defence use , and following the decommissioning of many obsolete cruisers and battleships after World War I , their 6 - inch Mk VII guns were also recycled for coast defence . 103 of these guns were in service in World War I in coastal defences around the UK . Some of these , together with others at ports around the wider British Empire , played an important defence role in World War II and remained in service until the 1950s . A number of new similar guns with stronger barrels which allowed more powerful cordite charges to be used were manufactured for coast defence during World War II , and were designated 6 - inch BL Mark XXIV . < br style = " clear : left ; " > Notable actions . In the German raid on Scarborough , Hartlepool and Whitby on 16 December 1914 , a notable action was fought by Durham Company RGA of the Territorial Force at Heugh ( 2 guns ) and Lighthouse ( 1 gun ) batteries defending Hartlepool . They duelled with the German battlecruisers and ( 11 inch guns ) and ( 8 . 2 inch ) , firing 112 rounds and scoring 7 hits . The battlecruisers fired a total of 1 , 150 rounds at the town and the batteries causing 112 civilians and 7 military killed . < br >