BL 18 inch Mk I naval gun The BL 18 - inch Mk I naval gun was a breech - loading naval gun used by the Royal Navy during World War I . It was the largest and heaviest gun ever used by the British . Only the Second - World - War Japanese 40 cm / 45 Type 94 had a larger calibre , , but the British shell was heavier . The gun was a scaled - up version of the BL 15 inch Mk I naval gun and was developed to equip the " large light cruiser " ( a form of battlecruiser ) . Three guns were built , but they did not see combat with the " Furious " , before they were removed from her and transferred to the s and for coast bombardment duties . Only 85 rounds were fired in anger before the war ended . All three were removed from service in 1920 and served as proving guns for cordite tests . Two were scrapped in 1933 and the last one survived until it was scrapped in 1947 . Design and development . The 18 - inch gun had its genesis in the insistence of the First Lord of the Admiralty , Admiral Fisher , for the biggest possible gun mounted on the fastest possible ship . He conceived of what he called " large light cruisers " carrying four guns , which became the , but he wanted their half - sister " Furious " to carry an even bigger gun . The Elswick Ordnance Company was the only company capable of manufacturing such a large gun and began design work in 1915 . It was designated as the " 15 - inch B " to conceal its real size and was derived from the design of the 15 - inch Mk I already in service . As mentioned above , these were wire wound guns whose construction generally resembled that of the 15 " / 42 ( 38 . 1 cm ) Mark I but with a relatively small breech ring . Construction consisted of inner A tube , A tube , wire - winding , B tube , jacket , shrunk on collar and breech ring . Over 200 miles ( 325 km ) of 0 . 25 × 0 . 06 in ( 0 . 635 × 1 . 52 cm ) of high - tensile steel wire was used . The Welin breech block use on these guns was significantly different in that the Vickers ' " pure couple " mechanism of the 15 " ( 38 . 1 cm ) was replaced with the Elswick short arm mechanism , for reasons of reducing " slam " as the breech closed . In this design , the breech screw withdrew through the carrier , which complicated the locking action . However , this mechanism was fast - acting , with about three seconds being needed to open or close the breech . The gun and its breech mechanism weighed a total of , almost half again as much as the 15 - inch gun ' s . It was mounted in a single - gun turret , also designated as the 15 - inch B , derived from the twin - gun 15 - inch Mark I / N turret . The barbette s of " Furious " were designed to accommodate either turret , in case problems arose with the 18 - inch gun ' s development . The gun could depress to −3° and elevate to a maximum of 30° . Ammunition development for the gun was naturally focused on anti - ship shells for the " Furious " , and it fired a , 4 crh armour - piercing , capped ( APC ) shell , at a muzzle velocity of to a distance of . It could fire one round per minute . The turret ' s revolving mass was , only a slight 2 % more than the of its predecessor . The guns proved to be too powerful for " Furious " light hull , and they became available for other uses during 1917 , after trials showed the ship could not handle the stress of firing . Admiral Sir Reginald Bacon , commander of the Dover Patrol , conceived a plan to mount two guns inside the shell of the Palace Hotel in Westende from where they could bombard the naval facilities at Zeebrugge and Bruges , provided that the hotel was captured during the upcoming Battle of Passchendaele . He planned to transport the guns across the English Channel lashed to the torpedo bulge s of monitors . He also thought that they could be used on the decks of monitors and as such a dual purpose carriage was designed for the guns , that could be used both afloat and ashore . Only a limited amount of traverse was required for either role , but elevation had to be increased to 45° to maximize range . The concept was approved 23 September 1917 , and Elswick was ordered to design the new ' B CD ' mounts for delivery in five months . The original concept for land use involved a special elevating slide that could traverse 6° to either side . Ammunition handling , elevation and ramming were to be done via hydraulic pump , but the breech was hand - worked . The gun was to be installed in a turf - covered concrete dome with a gunport for the barrel . As much as possible of the gun and its mount was designed to be assembled out of range of German artillery and then moved on a special broad - gauge railway to the site on specially - designed wheels . The transportable section weighed . After the British Army failed to capture Westende , the mounting was optimised for use on a monitor . It was very simple , consisting of two large girders connected together at each end with the gun and its carriage between them . The mount could only traverse 10° inside its fixed , ½ - inch ( 12 . 7 mm ) gun shield and was aimed over the starboard side of the monitor . It was loaded at a fixed angle of 10° , but it could only fire between 22° and 45° to equalize the stresses on the carriage and the ship . It was provided with hydraulically powered cranes , loading tray , rammer and breech mechanism to minimize the crew ' s workload , but the ammunition parties had to use muscle power . The shells were stowed below deck and had to be moved by overhead rail to the hatch in the deck behind the gun to be lifted up and loaded . The cordite propellant charges were kept in eighteen steam - heated storage tanks mounted on the forecastle deck abaft the funnel and moved to the gun on a bogie mounted on rails , two one - sixth charges at a time , which reduced the rate of fire to about one round about every 3 – 4 minutes . The monitors had to be extensively modified to handle the gun . Numerous additional structural supports had to be added underneath the gun to support its weight of ; the sides had to be plated in to accommodate the additional crewmen and the interior rearranged for the 18 – inch shells and the loading arrangements . Service . A total of three guns were built by Armstrong Whitworth , two for " Furious " and a spare . The forward gun was removed from " Furious " in March 1917 , before she was completed , when she was ordered to be converted to a seaplane carrier . The second gun was removed later in 1917 , and she was converted into an aircraft carrier . The new ' B CD ' mounts were delayed , and the mount for was not delivered until 20 June 1918 . The gun from " Furious " ' A ' turret was lifted aboard on 9 July , but the " General Wolfe " was not ready to begin firing trials until 7 August . She was given the nickname of ' Elephant and Castle ' , as the enormous gun - mount structure dominated the ship ' s profile . While the new mounting was being designed , further effort was put into the ammunition to extend the range as much as possible . Use of a supercharge , where one of the six charges was increased in weight to , making a total of propellant , and increasing the elevation to 45° extended the range to about with the existing 4 crh shells . New 8 crh high explosive shells , with a longer , thinner ballistic cap , were ordered , but only two shells had been delivered before the end of the war . Some of the existing stock of 500 APC and 500 CPC ( common , pointed , capped ) shells on hand from " Furious " were modified with the new cap and were probably the only shells used during the war . The " General Wolfe " was assigned to the Dover Patrol on 15 August 1918 , but did not fire on any targets until 28 September , when a large force of monitors was gathered to harass German lines of communication . She was anchored bow and stern , broadside to her target , and had difficulties dealing with the tidal currents . She opened fire on the railway bridge at Snaeskerke ( south of Ostend ) at a range of and made naval history as the heaviest shell fired from the largest gun at the longest range in action to date . She fired 52 shells that day and found that the recoil from her 18 – inch gun moved her sideways with her shallow hull and also caused her to roll , which slowed her rate of fire . She fired a total of 81 rounds before the end of the war . The second gun , " Furious " spare , was mounted in , but she was not ready for combat until 13 October 1918 . She fired three rounds the following day , but had to cease fire to avoid hitting friendly advancing troops . One round had already been loaded when the order came to cease fire so she fired it , with a reduced charge , into a minefield to seaward . A total of 85 18 - inch shells were fired in action by both guns . Wear on " Wolfe " s gun was measured at about 0 . 37 inch after firing 161 effective full charge s ( EFC ) - 105 rounds including proof and practice , with 57 being supercharges . This indicates the gun would have been good for well over 300 EFC , comparable with most other British ordnance using Cordite MD . The third gun , from " Furious " ' Y ' turret , was intended for , which had been modified to accept it earlier in the year , but the war ended before it was mounted , although the monitor was ordered to Portsmouth to have it fitted on 19 October . The guns were removed from the monitors in December 1920 . Gun No . 1 , from " Furious " ' Y ' turret , was lined down to and used in cordite - proving tests for the BL 16 - inch Mk I gun , intended for the cancelled G3 battlecruiser s , and used in the s . It remained in use until 1942 and was scrapped in 1947 . The other two guns were used at Shoeburyness and Yantlet artillery ranges in the Thames Estuary for similar duties ; they were scrapped in 1933 . One mount survived and was used to mount a spare BL 14 - inch Mk VII gun from the battleship . It was emplaced near Dover in 1940 , and the combination was named " Pooh " , after Winnie - the - Pooh .