Royal Garrison Artillery The Royal Garrison Artillery ( RGA ) was an arm of the Royal Artillery that was originally tasked with manning the guns of the British Empire ' s forts and fortresses , including coastal artillery batteries , the heavy gun batteries attached to each infantry division , and the guns of the siege artillery . History . The Royal Garrison Artillery came into existence as a separate entity when existing coastal defence , mountain , siege and heavy batteries of the Royal Artillery were amalgamated into a new sub - branch . A royal warrant provided that from 1 June 1899 : " . . . the mounted and dismounted branches of the Royal Regiment of Artillery shall be separated into two corps . . . to be named respectively ( a ) the Royal Horse Artillery and the Royal Field Artillery : ( b ) the Royal Garrison Artillery . " The Royal Regiment of Artillery , thenceforth , was divided into four branches . Other than mounted or unmounted dress , the obvious distinction in uniform was by the shoulder title badges : RGA ; RFA ; RHA ; and RA ( for the branch tasked with managing ammunition dumps and supply to units in the field ) . The RGA retained the badge and dress uniform ( dark blue with scarlet facings ) of the Royal Regiment of Artillery , but personnel were normally clothed and equipped as dismounted men . After 1920 all RGA personnel were classified as mounted men , whether serving in horse - drawn , mountain or tractor - drawn batteries , From 1914 when the army possessed very little heavy artillery , the RGA grew into a very large component of the British forces on the battlefield , being armed with heavy , large - calibre guns and howitzers that were positioned some way behind the front line and had immense destructive power . The corps name was discontinued in 1924 , when the RGA was re - amalgamated into the Royal Artillery . Pre - World War I mobile artillery tactics . Prior to the First World War artillery would manoeuvre on the battlefield beside the infantry and cavalry . The field artillery would form part of a battle line alongside the infantry and , on occasion , the horse artillery would charge alongside the cavalry with guns , limbers and caissons and all . Use of fixed artillery . Fixed artillery ( that which is not meant to move , other than for the purpose of aiming ) was placed in forts and batteries in locations where they might protect potential targets ( ports , cities , etc . ) from attack , or from where they might prevent the advance of an enemy . This included forts and batteries intended to protect against military forces on the land , and against naval forces on the sea . Coastal artillery relied primarily on high velocity guns , capable of striking out at ships at a great distance , and penetrating their armour . Inland defensive batteries might have armament better suiting use against personnel . Mobile ( field ) artillery pieces were sometimes used that could be quickly re - deployed as required between fortifications that were not permanently manned or armed . Fixed batteries were operated , in the late 19th and early 20th Centuries , by the RGA and Militia Artillery reservists ( often with support from other units , such as engineers operating searchlights for night - time firing ) . Conventional wisdom held that a naval force would need a three - to - one advantage over coastal artillery , as the land - based artillery had the advantage of firing from a fixed platform , with resultant advantages in accuracy , especially as range increased . By the start of the 20th century , the increasing size of the capital ships of the world ' s largest navies , and of the guns they wielded , was already sounding the death knell of coastal artillery . As the primary armament of battleships and battle - cruisers reached 16 inches , while coastal artillery was typically 6 inch or 9 inch guns , a large naval force , including capital ships , could level coastal batteries from a range that kept them out of reach of answering fire . The advent of artillery had changed the design of fortifications centuries before , spelling the end of high - walled castles . By the 20th century , fortifications were being designed with as much surrounding embankment by earthworks as possible . While this provided some protection from direct fire , it made defense against infantry more difficult , and did nothing to protect from high trajectory fire landing from above , or from air - bursting explosive shells , which rained the area enclosed by walls with shrapnel . In Bermuda , in the latter part of the 19th Century , where the War Office had expended vast fortunes building up fortifications to protect the Royal Naval Dockyard , it was decided belatedly that the Dockyard ' s own fleet of naval vessels could provide a more effective defence . With the advent of the aeroplane , and the missile , fixed artillery was both superseded and too vulnerable to continue in use . The last coastal artillery was removed from use in the 1950s . First World War . With the new long - range small arms available to the infantry in the era before World War I , artillery fighting in the infantry line was increasingly brought under fire . The solution to this was the principle of standing off and engaging the enemy with indirect fire . However , even after this became official military doctrine , field and horse artillery on both sides kept trying to fight in the old way . One instance was a gun duel fought between British and German horse artillery units using open sights during the Retreat to the Marne . In the quagmire of trench warfare that followed it was finally realised that it was not the place for the artillery to be in the infantry line . Henceforth the artillery would be positioned well behind the infantry battle line , firing at unseen targets , at co - ordinates on a map calculated with geometry and mathematics . As the war developed , the heavy artillery and the techniques of long - range artillery were massively developed . The RGA was often supported by the Royal Flying Corps ( RFC ) who had devised a system where pilots could use wireless telegraphy to help the artillery hit specific targets . The RFC aircraft carried a wireless set and a map and after identifying the position of an enemy target the pilot was able to transmit messages such as A5 , B3 , etc . in morse code to a RFC land station attached to a heavy artillery units , such as Royal Garrison Artillery Siege Batteries . The Siege batteries ( such as 9th Siege Battery at the Battle of the Somme ) had the largest guns and howitzers ; mounted on railways or on fixed concrete emplacements . Ammunition supply to the Royal Field Artillery ( RFA ) and other field artillery units was normally the role of the Royal Artillery : that part of the " Royal Regiment of Artillery " which retained the Royal Artillery ( RA ) shoulder badges . However during the war the RGA , which had large numbers of men idling in fortified batteries around the World with little chance of seeing action , provided a draft of sub - units to the Western Front to assist with ammunition supply in the field , and the operation of supply dumps . Re - amalgamation . As noted above the artillery arms were re - amalgamated into the Royal Artillery in 1924 and the RGA then ceased to exist as a separate entity .